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J Cell Biol. 2018 Aug 6;217(8):2691-2708. doi: 10.1083/jcb.201802138. Epub 2018 May 23.

Microtubules grow by the addition of bent guanosine triphosphate tubulin to the tips of curved protofilaments.

Author information

1
Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO richard.mcintosh@colorado.edu.
2
Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO.
3
Advanced Electron Microscopy Facility, University of Chicago, Chicago, IL.
4
Department of Physics, Lomonosov Moscow State University, Moscow, Russia.
5
Center for Theoretical Problems of Physicochemical Pharmacology, Russian Academy of Sciences, Moscow, Russia.

Abstract

We used electron tomography to examine microtubules (MTs) growing from pure tubulin in vitro as well as two classes of MTs growing in cells from six species. The tips of all these growing MTs display bent protofilaments (PFs) that curve away from the MT axis, in contrast with previously reported MTs growing in vitro whose tips are either blunt or sheetlike. Neither high pressure nor freezing is responsible for the PF curvatures we see. The curvatures of PFs on growing and shortening MTs are similar; all are most curved at their tips, suggesting that guanosine triphosphate-tubulin in solution is bent and must straighten to be incorporated into the MT wall. Variations in curvature suggest that PFs are flexible in their plane of bending but rigid to bending out of that plane. Modeling by Brownian dynamics suggests that PF straightening for MT growth can be achieved by thermal motions, providing a simple mechanism with which to understand tubulin polymerization.

Comment in

PMID:
29794031
PMCID:
PMC6080942
DOI:
10.1083/jcb.201802138
[Indexed for MEDLINE]
Free PMC Article

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