Tip:
Highlight text to annotate it
X
Hello. I am Ron Vale. I am a professor
at the University of California, San Francisco
and an investigator with the Howard Hughes Medical Institute.
And in these three lectures, I would like to tell you about
biological motility. Now there's some types of biological motility
that everyone is familiar with.
For example, the contraction of your muscles
or maybe the movement of ***
or the beating of cilia and flagella.
But it is also true that the interior of all eukaryotic cells
is teeming and bubbling with all kinds of intracellular motility
Let me take you here into the interior of a squid giant axon
seen in real time through a video microscope
Very much like the original experiments of Bob Allen, Scott Brady,
and Ray Lasek. And what you can see here
is a tremendous amount of motility.
All kinds of small organelles which are traveling between
the nerve cell body and the distal nerve terminal.
And these long snake like things here are mitochondria.
They are also moving through this very dense cytoplasm.
Indeed if you turn a microscope to any eukaryotic cell
you will see lots of intracellular motility like this.
Here is another prominent example
of intracellular motility: the process of cell division.
Here the DNA in green, the microtubules in red
the DNA congresses to the middle and then
the physical separation of the sister chromatids
to equally partition the genetic material.
Now all of this fantastic intracellular motility is driven
by biological machines called molecular motors.
And that is going to be a major subject of these lectures.
And just to get you in the right spirit
for thinking about these molecular machines,
I'd like to show you an animation developed by XVIVO
in conjunction with Harvard and the Howard Hughes Medical Institute
that takes you into the interior of the cell to show you a little bit
about what these machines might be doing.
What I hope you can appreciate from that remarkable video
is that the cell interior is packed with interesting machines.
Maybe they don't work exactly as they're shown in the video,
but the spirit of the video shows
that the inside of cells is very complicated.
There are lots of molecular machines that are working together
to create all of this complex cell behavior
that makes cells function and execute a number of complex behaviors
and abilities. And, so our goal, as scientists is to try to understand
how cells work, how these machines work in cooperation.
And by analogy, this is a very hard problem, by analogy
let's imagine coming up to this chemical plant here,
also a very complicated enterprise
without a particular degree in chemical engineering or having
the benefit of watching this chemical plant
being constructed in the first place.
And this is a little bit analogous to what we are trying to do in biology:
figure out how complex systems work. So what can we do?
Well, we can come up to this chemical plant
and watch it, we can see people coming in and out of the plant
and trucks transporting material,
machines in action in this chemical plant
and this is a little bit analogous to what we do
as cell biologists with microscopes is to watch cell behavior
and deduce how cells work from just observation.
We could also measure material flowing into this plant
We can see chemicals coming in and various chemicals coming out
of this plant, and follow the flow of material through this system...
maybe a little bit like what systems biologists are trying to do these days.
We could also take another route of disabling.
We could get our sledgehammer
out here and disable part of the machinery
and from that we can maybe deduce what parts
of the machine in the chemical plant
are performing what kind of function.
That's a little bit what geneticists do.
And, indeed in the third part of my lecture I'd like to show you
how all these three tools can be applied to understand
one type of intracellular motility and a very
complex structure, which is the mitotic spindle.
But in addition to studying this whole factory
as a whole here, we can also appreciate
that if we walk inside the factory,
we'll find that it is made up of remarkable machines
such as this steam belt here.
And each of these individual machines is very precisely engineered
to exact specifications for its function
and regulated in a number of important ways
And, it's the function of many of these machines
that make this chemical plant work
And in fact, we need to know in fact the details
of how each of these machines work
if we are going to understand also how this chemical plant
functions as a whole.
And indeed that is another important aspect of biology
and the second part of this lecture,
I'll give you a tour of one fascinating molecular machine
which is the cytoplasmic dynein motor.
And the tools we use to try to understand how this machine works.
But it's this part of the lecture that,
the rest of this section of the lecture,
I'd like to tell you a little bit about these machines
which are molecular motors and discuss
their activities in a general introduction.
So there are three classes of cytoskeletal motor proteins:
there's kinesin, myosin, and dynein.
And these motor proteins use chemical energy from ATP,
and they use this energy to move uni-directionally along a track.
I should...These are going to be the main focus of my lecture,
but I should also stress that there are
many other kinds of molecular motors in biology.
In addition to these cytoskeletal motors,
there are motors, for example,
that move along DNA or also RNA as well: helicases, polymerases.
There are also rotary motors, motors that spin around
such as motors that drive the bacteria flagellum
and there's also a remarkable rotary motor
inside of your mitochondria
that spins around like a turbine and makes ATP.
That's the engine that makes all the ATP in your cell,
and that's the F1/F0 ATPase.
So what are these molecular motors?
Well, I thought I would start off
by comparing them to engines that you are more familiar with
for example, an automobile engine.
Naturally these protein motors
are much smaller, and they are truly nanoscale engines.
Now, we often tend to use the term "nano"
to describe things that are small but maybe not that small,
like this iPod nano. While small, it really is not nanoscale.
But, these molecular motors that I am going to be talking about,
such as kinesin truly work at the nanoscale level.
They are about 10 to 50 nanometers in size.
Now, like your car engine, they also need a fuel source
and they use a chemical fuel,
which is ATP to produce their work.
Comparison to hydrocarbons for your automobile.
They move at a few millimeters per hour,
which maybe seems pathetically slow compared to your car
moving on the highway.
But, if you actually do the calculation
of how fast these motors are moving
relative to their own length per unit time, they're actually doing..
moving several times faster than your car engine is on a highway.
Now, for those of you who have filled up your gas tank recently
I am sure you would also appreciate
another virtue of these protein motors
and that is that they are much more work efficient
than the pitiful combustion engine in your car
which works at 10% efficiency.
These molecular motors work at 60% efficiency.
Some even work at 95% efficiency or more.
So, in fact, I think engineers
trying to design better types of machines
can learn a lot from how these biological machines work.
So, why should we study these cytoskeletal motors?
Well, I'd like to give you a few reasons why.
First reason for me personally, I think this is a fascinating subject.
I think one of the things that everyone appreciates about living organisms
is that they are endowed with the ability to move.
And, scientists going all the way back to the Ancient Greeks
have developed theories about how biological motion works
And, as I think you'll see in this and the next lecture,
we finally have the tools, we are right now in an epic of time
when we have the tools to understand this very old question in biology.
Second of all, these cytoskeletal motors
work in so many aspects of biology,
whether you are a neuroscientist,
whether you are a developmental biologist,
someone interested in signal transduction pathways,
or membrane trafficking, invariably some element
of your problem involves some kind of cytoskeletal motor
that is involved in producing the activities
that varied scientists study.
And, finally, and I hope to illustrate the last part of this lecture,
studying these cytoskeletal motors also has a number
of pragmatic benefits and relevance to medicine.
So first of all, we know that transport defects
either by mutations in molecular motors
or molecular motor associative proteins
can give rise to transport defects
that can cause disease, for example, neurodegenerative
diseases and in other cases, birth defects.
And in addition, we are also beginning to find that drugs directed
against motor proteins, either to inhibit their actions
or even enhance their actions
can have therapeutic benefit for human disease.
And that's something that I would like to illustrate
at the end of this lecture and also at the end
of the third part of this lecture as well.
So let me now dig in a little bit and tell you a little bit more
about the components of these molecular machines
So, for cytoskeletal motors, they work along tracks,
and there are two main tracks that are used to produce motion.
One is the microtubule shown here, and it's a cylindrical polymer
made up of repeating subunits of alpha and beta tubulin.
Another type of track is the actin filament, which I show over here.
It is made up of a single protein
called actin arranged in this helical polymer.
And if you want to know more about this actin filament,
I encourage you to watch the lecture by Julie Theriot
and she discusses actin in much more detail.
Now, these particular tracks here
are what these molecular motors run along
and the actin track serves as a substrate for myosin.
This is a cryo-EM of the myosin motor domain decorating actin.
And, microtubules serve as the tracks for two classes of motors
which are kinesin and dynein.
You can also see that these tracks
are segregated in different regions of the cell.
The actin filament is surrounding the outside of the cell,
and the microtubules are more interior
such as shown in this mitotic spindle.
Now one other thing you need to know
about these tracks is that they are polar.
They are polar structures.
Each of the subunit proteins that make up
actin and microtubules are themselves polar, they are asymmetric
and these subunits polymerize in a head to tail manner.
And that results in a net polarity of the whole filament.
In addition, these filaments are organized with uniform polarity
in the cell, so for example, with microtubules
what's called the minus end of the microtubule
is located at the pole of this mitotic spindle
where as the plus end is extending out
to these blue chromosomes over here.
Now this polarity is also true in Interphase cells as well.
Here is just a generic fibroblast with
microtubules extending all throughout the cell
but in an organized fashion.
The minus ends of these microtubules
are found at the center, at a place called the centrosome
and then these microtubules extend out,
their plus ends extend out to the periphery of the cell.
I should also say that the motors recognize this polarity
and a given motor will only move in one direction along this track.
So the combination of having polarized filaments
that are organized in this uniform manner in the cell
in conjunction with motors that move in one direction,
creates a fantastic transport system for the cell
that allows certain cargos to move to the distal periphery of the cell,
and other types of cargos to concentrate in the cell center.
Okay, let me now introduce you to the motor proteins
and show you a little bit more what they look like.
Here is a kinesin motor that is moving along a microtubule track
and the functional engine of this motor is shown here in purple
right over here. Its these purple domains of the kinesin molecule
that are churning up the ATP and moving along this microtubule track.
Beyond this so-called motor domain,
the rest of the molecule is referred to as the tail domain
and you can see here, in the case of kinesin, part of the tail domain
is an alpha helical coil-coil
and that dimerizes two kinesin polypeptides together,
which is very common for many motor proteins.
At the far end of the kinesin motor is another part of the tail domain
that docks this motor onto a particular cargo in the cell.
Here shown kinesin docking onto a membrane organelle
to specifically transport this cargo inside of the cell.
Now, one thing, when I refer to kinesin or myosin or dynein,
I am not referring to one motor,
but actually a big class of related motor proteins.
For example, kinesin is not one motor,
but in the human genome there are 45 different kinesin genes.
And the reason why there are so many is that these different kinesins
are specialized for different types of transport activities.
That's why there are so many of these kinesins because
they perform a whole variety of different kinds of transport functions.
Some kinesins are involved in moving
intracellular membrane organelles
like I showed you in the squid giant axon movie.
Other ones are moving mRNAs or proteins,
yet other ones are transporting building blocks
up, up to the tips of cilia and flagella.
And that's how...that helps these structures grow.
Yet other kinesins are involved in signaling transport, signaling pathways,
and whole other groups of kinesins
are involved in creating the mitotic spindle.
as I showed you in that earlier movie from a Drosophila embryo.
And in moving chromosomes as well.
And these many kinesins actually have a variety of different architectures
they have a similar motor domain, here shown in blue,
but if you just scan at this, the tail domains
of these kinesins all look very different from one another.
And that allows them to attach to different cargos,
and also be regulated in a number of different ways inside of the cell.
Now, the topic that I would like to finish
this particular part of the lecture
is how do these motor proteins actually work?
How do they produce motion?
Here, for example is the kinesin motor
transporting plastic beads along a microtubule.
And we'd like to know in detail, how does this work?
How is it that a very small protein molecule
is able to convert chemical energy
into this remarkable uni-directional motion?
Now, for the start, I could tell you that these motor proteins are enzymes.
So they hydrolyze ATP and use that chemical energy
to produce the work that you saw in that last video.
So, for example, M is for motor protein here; it binds to an ATP molecule;
it hydrolyzes it; and then it releases the products in a sequential manner.
And during this one ATPase cycle, the motor produces work
and some kind of step along its cytoskeletal track.
So, for that to happen, the protein itself
has to undergo some kind of structural changes
during this enzymatic cycle that allows it to walk along the track.
And the real goal of the field is to understand how all these transitions
in this enzymatic cycle result in changes in the protein structure
and ultimately explain the motion that we see in these videos.
Now, what I'd like to do is to take you to two animations
that were made by Ron Milligan, Graham Johnson, and myself.
And, they really re-capitulate decades of work by
hundreds of investigators studying this problem.
And this movie here shows the myosin motor
and how it's thought to work.
This is a myosin motor that might be found in your muscle
and the goal of this myosin is to bind to this actin track
and slide the actin filament so that your sarcomere
can contract and your muscle can contract.
And I'll show you that at the very end of this lecture.
Let's see know how it works. Here's the motor domain, here.
It binds to the track; it releases phosphate.
Actin causes phosphate release,
and that causes a big rotation of part of that motor.
A ten nanometer displacement
that is the part that causes the movement.
Now ATP comes in. That kicks the motor off the actin filament;
hydrolysis occurs and re-*** the motor so now
it can bind to a new filament and undergo a stroke.
Here it is again. Phosphate release. The stroke.
ATP binding. Detachment and re-cocking.
And it's millions of these events that happen in your muscle.
Many of these cyclic binding, stroke,
release events that result in the contraction of your muscle.
Now myosin is made to work in these big ensemble arrays
with millions of other myosin molecules causing muscle contraction.
But other motors in the cell have to do it solo.
This is a kinesin motor here.
And it may be attached way up here somewhere to its organelle cargo
and it's thought that even a single kinesin molecule
or maybe just a few kinesin molecules
are what are transporting organelles,
and mRNAs, proteins inside of cells.
So, the kinesin motor has to be very good, even acting solo,
to move along, continuously along a track without letting go.
Very different from muscle myosin
which can detach for most of its cycle,
just produce a brief stroke, and then release.
So let's see how this works. First of all here is the motor domain.
And now it binds to the microtubule.
The microtubule kicks off ATP. ATP comes in here,
and now look at this yellow element here. It zippers up
along the side of the enzyme, and you will see in the next one here,
that zippering causes the rear head
to be displaced from the rear binding site
and to move to a forward binding site over here.
So, it's this motion of what we call the neck linker here
that pulls the rear head from this forward binding site.
It moves around randomly, locks onto a new binding site.
And in this way the motor can work in what we call
a hand over hand manner to move continuously along a track.
And in fact, it can move for hundreds of ATPase cycles without letting go
due to these coordinated action of the two heads of the kinesin motor protein.
So, these animations recapitulate a lot of data.
I should say, you should always be careful about models like this
because, you know, no doubt they are not correct in every detail,
and I should say that scientists are still working out
many of the detailed mechanisms of both kinesin and myosin.
So these models are continuously being refined.
But how do we get to a model like this in the first place?
How do we collect data that even gets us close
to thinking about a protein at this level of detail?
So that's what I would like to tell you about:
how do you study the mechanism of a molecular motor?
Well there are several tools that we can use.
Very powerful tools that we're endowed with
in modern biophysics right now.
So, one thing that we'd like to know is what the motor looks like.
And we'd like to know this in incredible detail, at atomic resolution detail.
So we know exactly where all of the amino acids
and the side chains are positioned in this motor.
And that's the job of X-ray crystallography.
Here is the structure, X-ray crystal structure
of the kinesin motor domain,
and what you can see is the ATP in the active site.
And this is a ribbon diagram and over here is a space-filling model.
And this was done by our lab
in conjunction with Robert Fletterick's lab at UCSF.
So, this is the detail that we really need to know to begin
to understand protein structure
and how it changes during this enzymatic cycle.
But, in the case of kinesin,
it also gave an answer to a very old question
in our field, which was, are kinesin and myosin at all related?
Well, before the kinesin crystal structure,
I think the answer that everyone thought was no.
Made sense. You know kinesin is a microtubule motor;
myosin is an actin based motor. If you look at them
they are totally different in size. Kinesin is shown here in red,
and this myosin motor domain is much bigger, as you can see here.
And in addition, if you asked a computer to line up
the sequences of these motors,
the computer came back and said
there's no sequence similarity between kinesin and myosin at all.
Aha. Well, surprise! We got the crystal structure of kinesin,
and looked at it in detail compared to myosin,
and in fact, there was a remarkable structural similarity
in the core part of these molecules surrounding the nucleotide.
And this shows beta-strands of kinesin
and myosin in yellow and green
and you can see there is a remarkable overlap
between the beta-strands in these two motor proteins.
In addition, all of the helices that you see here for kinesin
overlap with similar helices in the myosin motor as well.
This is no accident.
This must indicate that the kinesin motor protein and myosin
evolved probably very distantly in evolution
from some kind of common ancestor.
And that made a huge difference in the psychology of the field.
People always thought, well, if I am studying myosin,
then, well, kinesin is another kind of motor
that I don't really need to pay attention to or vice versa.
But this information indicated that the myosin field and the kinesin field
were really studying variations on a common kind
of motor that evolved very early in evolution.
Not only that, but the structures of the motors
also reveal the surprising similarity to a whole other class of proteins,
which are the G proteins here
which people don't even think about
as conventional motor proteins.
But they also bind nucleotide, GTP; hydrolyze it to GDP,
and they need to change their shape in order to act
as switches in signal transduction cascades
and other kinds of activities like that.
And indeed, looking at the structures here in yellow,
there was a common core element surrounding
the nucleotide that was similar in these proteins.
So, we have some guess now about how all these machines evolved.
Probably very distantly in evolution, there was a great invention:
a nucleotide switch. Something that learned to bind nucleotide,
hydrolyze it, but not only just hydrolyze it, learn to change its shape
when it went from three phosphates to two phosphates,
like ATP to ADP or GTP to GDP.
This gave rise to two different kinds of machines,
the G protein family and some motor precursor that may still exist
in biology or may have been lost,
but probably was evolved very early in evolution.
And this motor precursor then evolved two different branches:
one motor that learned to walk on microtubules,
another motor that learned to walk on actin.
And wow! This was such a great invention that evolution
then gave...produced many subclasses of these motors;
a whole bunch of different kinesins, as I described to you;
a whole bunch of different myosins.
Now, in addition to getting some idea of the history of these motors,
we also just learned a lot by comparing these structures to one another.
And I don't have time to go into this in great detail,
but what seems to be the most ancient and common
theme that is shared between myosin and kinesin
and even G proteins, is how these proteins bind nucleotide,
hydrolyze it, and then change their shape when the protein
goes from an ATP to an ADP state, or a GTP to a GDP state.
So, the nucleotide switching mechanism seems to be
very similar in all these proteins, this core element, here, shown in blue.
But, on to this core switching part of the motor, of the enzyme,
Nature has plugged in a bunch of different mechanical elements.
Here is the myosin mechanical element,
this big huge lever arm that you saw rotate.
And in kinesin, there's this much smaller, little peptide
that threw the partner head forward.
So, the mechanical elements have learned to work
with this kind of common switch unit.
And in fact even in the myosin and kinesin families,
there are a number of different variations
on the types of mechanical elements and how they work.
Now, the one thing you can't get from crystal structures,
yet, people have been trying
but we haven't had a crystal structure of a motor with its track.
So, all the information that we have of that has
been derived from cryo-electron microscopy.
Here shown a cryo-electron micrograph reconstruction
from Ron Milligan's lab, the microtubule in gray over here
and this microtubule is decorated with a whole bunch of kinesin motors...
a special type of kinesin motor called Ncd.
And, from this we can get lower resolution, but very valuable
information on how the motor interacts with its track.
Particularly valuable if we combine this with X-ray crystallography,
and here shows this web like structure,
which is the information from cryo-EM
and what can dock into that the atomic structure
for this kinesin motor protein.
And these two in combination gives a very good idea
of exactly how this motor protein is interacting with the track
and how the track might be influencing the behavior of this motor.
Now, we can't get everything from cryo-EM and X-ray crystallography
because these are static techniques.
We just get a snapshot of the motor.
But we know that motors are very dynamic.
Here they are transporting beads along microtubules.
So, we need to study the dynamics of how they produce motion,
and we have great assays for doing that.
In fact, we can take these things out of a cell
and reconstitute motility in a test tube.
We can purify the motor protein. Purify the track.
Add some cargo like a bead here. Add ATP,
and the system takes off, and we can see that here.
In fact this was the original bead motility assay
that gave rise to the purification
of kinesin in the first place in the mid-1980s.
Here is another type of assay. In this assay the motor protein
is attached onto a glass slide
and then microtubules...so the motor proteins are fixed.
The microtubules are added; ATP is added.
And then these motor proteins grab hold of the microtubule,
and then they are transporting these
microtubules along the surface.
If you follow any of these microtubules here,
you can see them kind of crawling
along the glass surface
as these motor proteins are transporting them,
grabbing hold of the microtubule and transporting it like a log.
So this assay is also still used today.
Now, another great tool that emerged out of these in vitro motility assays
was the ability to study actually motility
at the level of individual molecules,
single molecular motors.
And this just shows some work from Joe Howard, Jim Hudspeth and myself
a number of years ago where the density of these kinesin motors
on the glass surface was spread out to very, very low densities,
so that only one motor could grab hold of the microtubule track.
And the position of that motor is shown right here,
and when the microtubule reaches the end of that kinesin molecule,
it then dissociates off in the solution. So that motion
of the microtubule that you see here,
and we can show this by statistical arguments,
is driven by a single kinesin molecule.
Now, subsequent to this time,
there are a number of other advanced techniques
that allowed us to understand how molecular motors work,
such as optical traps, which I'll show you in the next lecture.
But here is classic work from Steve Block's lab, which used an optical trap
to measure individual steps by a single molecule.
Here just shows a kinesin transporting a bead
and its stationary over right from here to here, and then it takes a jump,
Boomp! That is one step, another step, another step.
And all of these steps here
are eight nanometers in size, very small.
And this eight nanometer dimension corresponds to the distance
between these stepping stones along the microtubule.
The distance between the alpha/beta tubulin monomers.
Now there are other cool assays that one can use too.
Here's an assay where a single fluorescent dye molecule
is added to a motor protein, a kinesin here,
and you can use a very specialized microscope,
I'll show you that in the next lecture,
that can track these single motor proteins
labeled with a single fluorescent dye
and here... these are kinesins that you can see here
traveling down this microtubule track.
Again, in real time, I should say.
Okay, so we have great assays and great tools
but, for us to really understand how motors work,
I think we have to get control of them.
We have to be able to manipulate them,
design, and make new motors.
And I really like this quote here from Richard Feynman,
because I think it also illustrates what we are trying
to do in the motor field to understand how they work.
And that is, to actually engage in, beyond evolution,
to try and design our own motors.
So we can take information on motors:
we know their sequences, we know their atomic structures.
And then from that we can say,
"Ah! From that I think this is how the
motor protein produces motion."
And then I can say, "Well, if that hypothesis is right, if that's true,
then I should be able to design a motor in this way
and produce some other kind of unique outcome."
Maybe change the direction which that motor moves,
change its velocity or other kinds of parameters.
And we have the ability
to make these motors in bacteria or other systems.
And then re-design these motor proteins, do protein engineering,
and then purify them and test them using all these assays,
like the in vitro motility assays that I showed you.
But there are a lot of other great assays,
we can look at their chemical cycles in great detail
by enzyme kinetic measurements,
or look at their conformational changes
by techniques like fluorescence energy transfer.
There's a whole bunch of assays that we can use.
And then we can see, well, from our hypothesis,
did the motor behave as we expected.
Well, maybe not quite. So we go back,
rethink our hypothesis, design another kind of motor
and then test it again. And it is through this cyclic mechanism
that you see here that we can begin
to understand how these machines work.
Now, in addition to just understanding the fundamental
nature of how these molecular motors work,
there are a lot of things that we can do that
can actually have a lot of pragmatic benefit for mankind.
So one thing that I will actually show you right now,
is it's possible to manipulate motors using small molecules
in ways that will allow us actually to modulate motor activity
in a way that's beneficial for improving certain human diseases.
And I'll show you that in this lecture and also on the last lecture, as well.
And it's also possible that we might be able to engineer motors
in ways that allow them to deliver drugs inside of cells
or produce new types of cell fate, or even outside of cells,
design motors that might be useful for certain types of nanotechnology.
Let me just talk about this right now, and I'd like to tell you a brief story
and this is not done in my lab.
This is done in a company which is called Cytokinetics.
I should mention that I am a co-founder of this company,
a shareholder, and also currently on the SAB.
But, I'd like to illustrate this story because I think it is a really great story
about how you can manipulate a motor
in a way that is useful for medicine.
And what I am going to just tell you about is a story
in ways in which one can actually use small molecules
to make myosin motors in the heart actually work better
to improve the contractility and produce cardiac output
for patients that have heart failure,
where their cardiac output has been compromised.
But first let me just tell you a little bit about the science here in this video.
I am going to walk of the screen here,
but what you'll see is a heart beating,
and then we are going to go down to the cellular level
and you'll see the sarcomere, the basic unit of myosin contractility,
where myosin filaments are pulling in actin filaments
to make the sarcomere contract
and that results in the contraction of the heart.
You'll also see these floating little speckles here,
which are calcium ions,
and those are the signals that control
a regulatory complex on the actin
made of tropomyosin and troponin that allows
the myosin to engage in the actin filament.
And, it's these cyclic flows of calcium that turn on the myosin.
Myosin work starts contracting
and that causes your heart to contract.
Okay, well, so that is how the heart is supposed to work,
but there are some people where the heart is not working properly
where their cardiac output is compromised.
The contractility of these ventricles is not working as it should.
And, that can result in severe health problems and also mortality.
So, we need to think of strategies for improving
the contractility in the heart.
There are many drugs that are out there,
several drugs that are out there on the market already
that work through the signaling pathways.
They work through controlling the output of calcium.
Now, that's a reasonable strategy, but these drugs also have side effects
because working through these signaling pathways
can also be very complex.
So, Cytokinetics, led actually by Fady Malik
who is my very first graduate student
that I had at UCSF who
became a cardiologist and then moved on
to start this cardiac program at Cytokinetics,
has led an effort to develop ways in which
one can activate the myosin to make it work better.
Now this is a pretty dramatic, bold strategy,
because most pharmaceutical companies develop drugs
to inhibit enzymes, and I can't really think of any other example
where there is a drug that activates a particular enzyme.
And at least, its a rare type of drug.
So, this was a bit risky, but they took this project
first of all and to find these drugs what they had to do
is reconstitute the motility system out of the heart an in a test tube.
And they did this by purifying actin, myosin, troponin,
and tropomyosin, reconstituting it all,
this whole system, in a test tube
and then they measured myosin ATPase activity
and what they were looking for were small molecules,
like this one that I'm showing you here
that would activate the ATPase of the myosin.
In other words, make it cycle faster
which should result in increased contractility of the heart
when the calcium, the natural calcium signal was signaling.
Now this was not an easy effort.
It involved doing biochemical screens and screening for hundreds
and thousands of molecules
to find one that showed this type of activity. And then after that,
there was a lot of chemistry that had to go on,
to refine the affinity and the pharmacokinetic
properties of these molecules
to make them suitable drugs to put into people.
But that did happen, and before that happened, they tested this.
Oh I should say, here is the...here is how they think it works.
It increases this particular step of the myosin cycle,
that step where the actin is tickling the myosins in some way
to force the phosphate out of the active site and cause the power stroke
and these drugs facilitate this particular step of the myosin cycle.
So, the knowledge of the biochemistry here has been
essential for the drug discovery process.
And here is what this drug looks like in a dog model here.
Here is the an echocardiogram showing the ventricle of the heart
in a dog contracting here. And the same heart
after giving this particular myosin activator.
And you can see that this heart is now contracting
much more vigorously, resulting
in increased cardiac output
and improved blood flow from this heart.
Now, after, so this is pretty dramatic, and this drug has also been
now in Phase I clinical trials in people,
and I can say that it basically...
echocardiograms in people show exactly this type of effect.
And now, the real issue is will this help people whose hearts are failing,
and will it result in improved health
for these individuals, and less mortality.
So that's what's happening right now.
These drugs are in phase II clinical trials,
and probably we'll find out if this program
did result in helping these individuals in a couple years.
So, I hope in this set of lectures here, this first lecture,
you can see that these molecular motors, they're fascinating machines.
We have great tools for studying them and these machines also...
understanding these machines do have pragmatic
outcomes for human health and disease.
So thank you, and in my second lecture
I'll talk about current work on our lab
on the dynein motor and the last set of..
the last lecture will be on understanding motility
in the context of the process of mitosis. Thank you very much.