Microtubule-associated proteins and microtubule-based translocators have different binding sites on tubulin molecule |
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Authors: | V I Rodionov F K Gyoeva A S Kashina S A Kuznetsov V I Gelfand |
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Institution: | A. N. Belozersky Laboratory of Molecular Biology and Bioorganic Chemistry, Moscow State University, Union of Soviet Socialist Republics. |
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Abstract: | It has been previously shown that a class of microtubule proteins, the so-called microtubule-associated proteins (MAPs), binds to the C-terminal part of tubulin subunits. We show here that microtubules composed of tubulin whose 4-kDa C-terminal domain was cleaved by subtilisin (S-microtubules) are unable to bind MAPs but can still bind the anterograde translocator protein kinesin and the retrograde translocator dynein. Binding of both motors to S-microtubules, like their binding to normal microtubules, was ATP-dependent. In addition, direct competition experiments showed that binding sites for kiensin and MAPs on the microtubule surface lattice do not overlap. Furthermore, S-microtubules stimulated the ATPase activity of kinesin at least 8-fold, and the affinities of kinesin for control and S-microtubules were identical. S-microtubules were able to glide along kinesin-coated coverslips at a rate of 0.2 microns/s, the same rate as control microtubules. We conclude, that unlike MAPs, kinesin and cytoplasmic dynein bind to the tubulin molecule outside the C-terminal region. |
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