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Publication Abstract from PubMed

Mg2+ is essential for guanosine triphosphatase activity and plays key roles in guanine nucleotide binding and preserving the structural integrity of GTP-binding proteins. To understand the structural basis for Mg2+ function during the GDP/GTP exchange process, we determined the crystal structure of Delta9-Sar1-GDP at low Mg2+ concentration at 1.8A. Two Sar1-GDP molecules in the crystal form a dimer with Mg2+ presenting only in molecule B but not in molecule A. The absence of Mg2+ induces significant conformational changes in the switch I region in molecule A that shows similarities with those of Ha-Ras bound to Sos. The current structure reveals an important regulatory role for Mg2+. We suggest that guanine nucleotide exchange factor may utilize this feature to generate an open conformation for GDP/GTP exchange. Furthermore, we propose a mechanism for COPII assembly and disassembly in which dimerization of Sar1 plays an important role.

An open conformation of switch I revealed by Sar1-GDP crystal structure at low Mg2+.,Rao Y, Bian C, Yuan C, Li Y, Chen L, Ye X, Huang Z, Huang M Biochem Biophys Res Commun. 2006 Sep 29;348(3):908-15. Epub 2006 Aug 1. PMID:16899220^[3]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.