Interactions between CLIP-170, tubulin, and microtubules: implications for the mechanism of Clip-170 plus-end tracking behavior.
CLIP-170 belongs to a group of proteins (+TIPs) with the enigmatic ability to dynamically track growing microtubule plus-ends. CLIP-170 regulates microtubule dynamics in vivo and has been implicated in cargo-microtubule interactions in vivo and in vitro. Though plus-end tracking likely has intimate connections to +TIP function, little is known about the mechanism(s) by which this dynamic localization is achieved. Using a combination of biochemistry and live cell imaging, we provide evidence that CLIP-170 tracks microtubule plus-ends by a preassociation, copolymerization, and regulated release mechanism. As part of this analysis, we find that CLIP-170 has a stronger affinity for tubulin dimer than for polymer, and that CLIP-170 can distinguish between GTP- and GDP-like polymer. This work extends the previous analysis of CLIP-170 behavior in vivo and complements the existing fluorescence microscope characterization of CLIP-170 interactions with microtubules in vitro. In particular, these data explain observations that CLIP-170 localizes to newly polymerized microtubules in vitro but cannot track microtubule plus-ends in vitro. These observations have implications for the functions of CLIP-170 in regulating microtubule dynamics.
Folker
Eric S
ES
Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46565, USA.
Baker
Brian M
BM
Goodson
Holly V
HV
D000818:Animals; D005454:Fluorescence Polarization; D019204:GTP-Binding Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D066298:In Vitro Techniques; D007734:Kymography; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism* / Q000648:ultrastructure; D008954:Models, Biological; D009363:Neoplasm Proteins / Q000378:metabolism*; D014404:Tubulin / Q000378:metabolism*
D008869:Microtubule-Associated Proteins; D009363:Neoplasm Proteins; D014404:Tubulin; C076744:cytoplasmic linker protein 170; D019204:GTP-Binding Proteins