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Globular Structural Proteins – Protein Movement and Cell Signaling

by Kevin Ahern, PhD
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    00:00 Now globular structural proteins are different. For example I talked about actin and I talked about a tubulin. Tubulin is a family of proteins that makes up the microtubules. Both of these globular structural proteins, tubulin and actin, self-assemble. So they make fibers by putting themselves together, and this is a fascinating process, each of which requires triphosphates. In the case of tubulin GTP is needed for the assembly and stability, in the case of actin, the polymerization requires the presence of ATP, as we shall see.

    00:36 Now actin is notable for making up the cytoskeleton, it's also very important for muscular contraction, for cell motility, cell division, cytokinesis, vesicle and organ movement, and cell signaling.

    00:48 So actin is very involved in a lot of movement processes inside of cells. We can see the assembly process for actin shown schematically in this illustration. Free actin is known as G-actin, and you can see that it's pretty much just a green ball shown on the top left of the illustration. Activation of G-actin starts with the binding of ATP by the G-actin molecules. At some point the activated G-actin molecules have an event called a nucleation event, and in that nucleation event, what happens is that there is a triad, or three actins that are placed together to start the polymer. Now that nucleation event requires interaction with other proteins and the different proteins can help the nucleation event to occur. One of the nucleation event proteins that can make that occur is a protein called formin. In any event, however the process starts, once it gets started, the polymerization happens quite readily and we can see the growth of the fiber going on and on, and the interwound strands that make up the actin fiber. At the very end, after the completion of this, we have what's known as the F-actin filament, and the F-actin filament is stabilized by the hydrolysis of ATP to ADP, resulting in the release of PI, that is the phosphate that you can see at the very bottom.


    About the Lecture

    The lecture Globular Structural Proteins – Protein Movement and Cell Signaling by Kevin Ahern, PhD is from the course Biochemistry: Basics.


    Included Quiz Questions

    1. They work mostly outside of cells
    2. Assembly/stability requires triphosphates
    3. The group includes tubulin and actin
    4. Are made up of monomeric polypeptide units

    Author of lecture Globular Structural Proteins – Protein Movement and Cell Signaling

     Kevin Ahern, PhD

    Kevin Ahern, PhD


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