how is the structure of kinesin related to its function? This is a topic that many people are looking for. g4site.com is a channel providing useful information about learning, life, digital marketing and online courses …. it will help you have an overview and solid multi-faceted knowledge . Today, g4site.com would like to introduce to you 033-Kinesin Structure & Function. Following along are instructions in the video below:
Will be our last video lesson on protein function from chapter five. And wellll be looking at the motor protein kinesin first of all its a modal that associates with microtubules thats its target protein. Remember with myosin our target protein.
Was actin. And it has a different role within the cell. However if we look at the figure at the top of the screen.
Here we see that the structure is very similar to that of myosin for each of the monomers. We have a globular head. We have a straight neck region and an alpha helical tail and then those tails form a coiled coil interaction to form our fundamental unit the dimer the other thing we notice and thats depicted in our cartoon structure here is that the neck is shorter in kinesin.
We still need those necks to move our heads. But the movement is slightly different and so we dont need to wrap those light chains around our necks to strengthen and support them in our movement. We still need light chains.
But they serve a different function and for that reason theyre at the other end of the molecule so remember with myosin. We had two light chains per neck for per dimer.
In this case. We have one light chain per monomer two in the dimer and the goal. The role of these light chains is to grab hold of a vesicle and were going to walk it from one end of the cell to the other so thats the other difference kinesin moves by stepping instead of grabbing remember with myosin.
We grabbed opposite muscle fibers and we pulled them together to contract the muscle in this case. Were going to pick up a vesicle and were going to walk or step. It from one end of the molecule to the other another similarity is that were going to move those heads by atp hydrolysis.
Now we notice another difference here and that is with myosin. Remember we bundled a bunch of those dimers together to form the thick filament. All the tails.
Associated together and multiple heads contacting our target protein actin. In this case. The fundamental unit is just the dimer because our goal is different we want to move that cargo from one place to another and we just need one set of heads to do that the other thing.
Thats different is remember with myosin. The heads worked independently of each other in this case.
However these two heads work like our two feet. We need both feet to walk in a forward direction. And we certainly dont need more than two feet.
So here we are were carrying our cargo bound to the end of our tails. And weve got the two heads here. Its bound to tubulin remember.
Tubulin is composed of alpha and beta tubulin alpha. In the darker blue and beta in the lighter blue and heres our what were going to call our leading head in orange. Its bound specifically to the beta subunit that will be our right foot for now and heres our left foot in yellow.
And its currently bound to adp and its not bound to tubulin. So this is our starting position. The first step in our sequence is the same as mice and that is were going to bind atp.
But the effect is very different remember with myosin when that head bound atp. It let go of the actin in this case.
However with kinesin once that head binds atp. It grabs on more tightly to that beta subunit and that produces a little bit of a kink in the neck. And that causes that trailing head and yellow to swing forward by about a hundred and eighty degrees.
So youll notice heres another difference. Remember our goal is to move that cargo towards that positive end and simply by moving my left foot forward. Im already moving in that direction.
So the force generating step is the first thing instead of the last thing as we saw in myosin. So here we are we have a new leading head thats in yellow here currently bound to adp and our new trailing head in orange is bound to atp as we swing that new leading head forward it quickly binds the next subunit of tubulin beta subunit and as it does so it releases its a adp. So now we have a new leading head in yellow bound to abate a subunit.
We have a new trailing head in orange and thats bound to atp in our next. Step that trailing head is going to hydrolyze atp and release inorganic phosphate. And its still bound to adp remember.
This is where our previous trailing head started. So now weve put our left foot forward and our right foot is up this is how the kinesin motor protein works it steps one foot forward at a time and each foot moves in relationship to one another so they dont work independently of one another they work in concert in cooperation with one another thats another distinctive difference and in this case.
Were moving in one direction. The cargo remains attached and the head one head is always bound. Were always moving in that forward direction until we get where we want to go and so we say that the movement is processive now one another way in which myosin and kinesin are similar is that theyre both part of a family called ntp aces.
Remember ntp stands for nucleotide triphosphate and ntp aces are enzymes that digest or hydrolyze. A nucleotide triphosphate. So that would apply both to kinesin and myosin because they hydrolyze atp in order to move their heads or levers.
Theyre also part of whats called a super family that is to say there are many examples of this and they have a phosphate binding loop. And so theyre called p loop ntp aces. Youll need this information.
And answering some of the homework questions. So an example of how we might use kinesin as a motor protein it might move cargo between the cell body of a neuron and its axons that can be quite a distance and so we need to make sure that its going to hold on to that cargo remember thats why we need the light chains and that its going to keep walking forward until it gets to where it needs to go this concludes. Our studies in chapter five in our next lesson well begin our studies in chapter six.
Well begin to examine a class of proteins that function as biological catalysts that is enzymes. Well see why there is a need for this class of proteins and in general. How they function will also be struck by the levels of reaction rate enhancement they make possible .
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