The 2-start helical assembly of dynamin dictates the organization of the plasma membrane fission machinery

Wednesday, September 24, 2014 — Poster Session IV
10:00 a.m. –12:00 p.m.	FAES Academic Center	NIDDK	STRUCTBIO-7

* FARE Award Winner

Authors

• AC Sundborger
• S Fang
• JE Heymann
• P Ray
• JS Chappie
• JE Hinshaw

Abstract

Dynamin organizes into helical assemblies at necks of clathrin-coated pits to promote membrane fission. Self-assembly stimulates the GTPase activity of dynamin. The transition-state of dynamin’s GTP hydrolysis reaction is required for fission. We have solved the structure of a transition-state-defective mutant, K44A, assembled on a lipid template, at 12.5 Å resolution using cryo-electron microscopy. In the presence of GTP, K44A constricts the underlying lipid to an inner luminal diameter of 3.7 nm, the theoretical limit for spontaneous membrane fission. Docking crystal structures of dynamin domains into our ‘super-constricted’ density map shows that only the GTPase domain ground state conformation fits. Moreover, K44A lacks stimulated GTPase activity. This suggests that the ground state conformation in deed is sufficient to achieve super-constriction and that super-constricted dynamin is trapped in a pre-hydrolysis, GTP-bound state. The super-constricted dynamin polymer adopts a 2-start helical symmetry, which results in the most efficient subunit packing and generates the highest possible number of GTPase domain interfaces. Thus, assembly of a 2-start helix allows super-constriction of the lipid and maximizes the G domain dimerization, achieving the highest possible GTPase activity. Hydrolysis may cause additional conformational changes in the super-constricted polymer, and polymer disassembly to further promote the fission reaction.

back to top