The Lattice As Allosteric Effector: Structural Studies of Alphabeta- And Gamma-Tubulin Clarify the Role of GTP in Microtubule Assembly

Journal Article · Thu May 21 04:00:00 EDT 2009 · Proc. Nat. Acad. Sci. 105:5378-5383,2008

OSTI ID:953061

Rice, L M; Montabana, E A; Agard, D A

GTP-dependent microtubule polymerization dynamics are required for cell division and are accompanied by domain rearrangements in the polymerizing subunit, alpha-tubulin. Two opposing models describe the role of GTP and its relationship to conformational change in alpha-tubulin. The allosteric model posits that unpolymerized alpha-tubulin adopts a more polymerization-competent conformation upon GTP binding. The lattice model posits that conformational changes occur only upon recruitment into the growing lattice. Published data support a lattice model, but are largely indirect and so the allosteric model has prevailed. We present two independent solution probes of the conformation of alpha-tubulin, the 2.3 A crystal structure of gamma-tubulin bound to GDP, and kinetic simulations to interpret the functional consequences of the structural data. These results (with our previous gamma-tubulin:GTPgammaS structure) support the lattice model by demonstrating that major domain rearrangements do not occur in eukaryotic tubulins in response to GTP binding, and that the unpolymerized conformation of alpha-tubulin differs significantly from the polymerized one. Thus, geometric constraints of lateral self-assembly must drive alpha-tubulin conformational changes, whereas GTP plays a secondary role to tune the strength of longitudinal contacts within the microtubule lattice. alpha-Tubulin behaves like a bent spring, resisting straightening until forced to do so by GTP-mediated interactions with the growing microtubule. Kinetic simulations demonstrate that resistance to straightening opposes microtubule initiation by specifically destabilizing early assembly intermediates that are especially sensitive to the strength of lateral interactions. These data provide new insights into the molecular origins of dynamic microtubule behavior.

• Research Organization: Stanford Linear Accelerator Center (SLAC)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC02-76SF00515
• OSTI ID: 953061
• Report Number(s): SLAC-REPRINT-2009-223
• Journal Information: Proc. Nat. Acad. Sci. 105:5378-5383,2008, Journal Name: Proc. Nat. Acad. Sci. 105:5378-5383,2008 Journal Issue: 14 Vol. 105; ISSN 0027-8424; ISSN PNASA6
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CELL DIVISION
CONFORMATIONAL CHANGES
CRYSTAL STRUCTURE
FUNCTIONALS
KINETICS
MICROTUBULES
Other
OTHER
POLYMERIZATION
PROBES