Mechanism of Tubulin Oligomers and Single-Rings Disassembly Catastrophe

15 April 2022, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Cold tubulin dimers coexist with tubulin oligomers and single-rings. These structures are involved in microtubule assembly, however, their dynamics are poorly understood. Using state-of-the-art solution synchrotron time-resolved small-angle X-ray scattering we discovered a disassembly catastrophe (half-life of about 0.1 sec) of tubulin rings and oligomers upon dilution or addition of guanosine triphosphate. A slower disassembly (half-life of about 38 sec) was observed following a temperature increase. Our analysis showed that the assembly and disassembly processes were consistent with an isodesmic mechanism, involving a sequence of reversible reactions at which dimers were rapidly added/removed one at a time, terminated by a two orders-of-magnitude slower ring-closing/opening step. We revealed how assembly conditions varied the mass fraction of tubulin in each of the coexisting structures, the rate constants, and the standard Helmholtz free energies for closing a ring and for longitudinal dimer-dimer associations.

Keywords

tubulin
tubulin single-ring
self-assembly
disassembly
SAXS
time-resolved SAXS

Supplementary materials

Title
Description
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Title
Supporting Information
Description
Supporting Information Available: Cryo-TEM Images, SAXS Models of Rings and Ring Fragments, Additional GDP-Tubulin Data, Steady-State After Ring Disassembly Catastrophe, Tubulin Single Ring Catastrophe Following Dilution, Tubulin Single Ring Catastrophe Following GTP Addition, and Tubulin Single Ring Disassembly Following a Temperature Increase.
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