Sun, 20 Jul 2008 21:07:59 BST CiteULike: cactus Rice http://www.citeulike.org/user/cactus/author/Rice CiteULike.org en-gb Copyright © 2004-2008 citeulike.org http://www.citeulike.org/user/cactus/article/2818408 <i>Structure, Vol. 16, No. 5. (7 May 2008), pp. 755-765.</i><br /><br />Summary Hsp90, an essential eukaryotic chaperone, depends upon its intrinsic ATPase activity for function. Crystal structures of the bacterial Hsp90 homolog, HtpG, and the yeast Hsp90 reveal large domain rearrangements between the nucleotide-free and the nucleotide-bound forms. We used small-angle X-ray scattering and recently developed molecular modeling methods to characterize the solution structure of HtpG and demonstrate how it differs from known Hsp90 conformations. In addition to this HtpG conformation, we demonstrate that under physiologically relevant conditions, multiple conformations coexist in equilibrium. In solution, nucleotide-free HtpG adopts a more extended conformation than observed in the crystal, and upon the addition of AMPPNP, HtpG is in equilibrium between this open state and a closed state that is in good agreement with the yeast AMPPNP crystal structure. These studies provide a unique view of Hsp90 conformational dynamics and provide a model for the role of nucleotide in effecting conformational change. Multiple Conformations of E. coli Hsp90 in Solution: Insights into the Conformational Dynamics of Hsp90 Kristin Krukenberg Friedrich Förster Luke Rice Andrej Sali David Agard doi:10.1016/j.str.2008.01.021 Structure, Vol. 16, No. 5. (7 May 2008), pp. 755-765. 2008-05-21T07:01:18-00:00 2008 Structure 16 5 755 765 chaperone structural_change structure xray-scattering http://www.citeulike.org/user/cactus/article/2744934 <i>Proceedings of the National Academy of Sciences, Vol. 105, No. 14. (8 April 2008), pp. 5378-5383.</i><br /><br />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. 10.1073/pnas.0801155105 The lattice as allosteric effector: Structural studies of alphabeta- and gamma-tubulin clarify the role of GTP in microtubule assembly Luke Rice Elizabeth Montabana David Agard doi:10.1073/pnas.0801155105 Proceedings of the National Academy of Sciences, Vol. 105, No. 14. (8 April 2008), pp. 5378-5383. 2008-05-02T10:24:15-00:00 2008 Proceedings of the National Academy of Sciences 105 14 5378 5383 allostery kinetics polymerization simulation structural_change xray-crystal-structure