2ii0

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Template:STRUCTURE 2ii0

Crystal Structure of catalytic domain of Son of sevenless (Rem-Cdc25) in the absence of Ras

Contents 1 Overview 2 Disease 3 About this Structure 4 Reference

Overview

The Ras-specific guanine nucleotide-exchange factors Son of sevenless (Sos) and Ras guanine nucleotide-releasing factor 1 (RasGRF1) transduce extracellular stimuli into Ras activation by catalyzing the exchange of Ras-bound GDP for GTP. A truncated form of RasGRF1 containing only the core catalytic Cdc25 domain is sufficient for stimulating Ras nucleotide exchange, whereas the isolated Cdc25 domain of Sos is inactive. At a site distal to the catalytic site, nucleotide-bound Ras binds to Sos, making contacts with the Cdc25 domain and with a Ras exchanger motif (Rem) domain. This allosteric Ras binding stimulates nucleotide exchange by Sos, but the mechanism by which this stimulation occurs has not been defined. We present a crystal structure of the Rem and Cdc25 domains of Sos determined at 2.0-A resolution in the absence of Ras. Differences between this structure and that of Sos bound to two Ras molecules show that allosteric activation of Sos by Ras occurs through a rotation of the Rem domain that is coupled to a rotation of a helical hairpin at the Sos catalytic site. This motion relieves steric occlusion of the catalytic site, allowing substrate Ras binding and nucleotide exchange. A structure of the isolated RasGRF1 Cdc25 domain determined at 2.2-A resolution, combined with computational analyses, suggests that the Cdc25 domain of RasGRF1 is able to maintain an active conformation in isolation because the helical hairpin has strengthened interactions with the Cdc25 domain core. These results indicate that RasGRF1 lacks the allosteric activation switch that is crucial for Sos activity.

Disease

Known disease associated with this structure: Fibromatosis, gingival OMIM:[182530], Noonan syndrome 4 OMIM:[182530]

About this Structure

2II0 is a Single protein structure of sequence from Homo sapiens. Full crystallographic information is available from OCA.

Reference

A Ras-induced conformational switch in the Ras activator Son of sevenless., Freedman TS, Sondermann H, Friedland GD, Kortemme T, Bar-Sagi D, Marqusee S, Kuriyan J, Proc Natl Acad Sci U S A. 2006 Nov 7;103(45):16692-7. Epub 2006 Oct 30. PMID:17075039 Page seeded by OCA on Sun May 4 07:31:43 2008