Summary: Insights into microtubule nucleation from the
crystal structure of human g-tubulin
Hector Aldaz1
*, Luke M. Rice1
*, Tim Stearns2
& David A. Agard1
Microtubules are hollow polymers of ab-tubulin that show GTP-
dependent assembly dynamics and comprise a critical part of the
eukaryotic cytoskeleton. Initiation of new microtubules in vivo
requires g-tubulin, organized as an oligomer within the 2.2-MDa
g-tubulin ring complex (g-TuRC) of higher eukaryotes1­3
. Struc-
tural insight is lacking regarding g-tubulin, its oligomerization
and how it promotes microtubule assembly. Here we report the
2.7-A° crystal structure of human g-tubulin bound to GTP-gS
(a non-hydrolysable GTP analogue). We observe a `curved' con-
formation for g-tubulin­GTPgS, similar to that seen for GDP-
bound, unpolymerized ab-tubulin4
. Tubulins are thought to
represent a distinct class of GTP-binding proteins, and confor-

Source: Agard, David - Department of Biochemistry and Biophysics, University of California at San Francisco
Stearns, Tim - Departments of Biology & Genetics, Stanford University

Collections: Biology and Medicine; Biotechnology