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  • Title: An open conformation of switch I revealed by the crystal structure of a Mg2+-free form of RHOA complexed with GDP. Implications for the GDP/GTP exchange mechanism.
    Author: Shimizu T, Ihara K, Maesaki R, Kuroda S, Kaibuchi K, Hakoshima T.
    Journal: J Biol Chem; 2000 Jun 16; 275(24):18311-7. PubMed ID: 10748207.
    Abstract:
    Mg(2+) ions are essential for guanosine triphosphatase (GTPase) activity and play key roles in guanine nucleotide binding and preserving the structural integrity of GTP-binding proteins. We determined the crystal structure of a small GTPase RHOA complexed with GDP in the absence of Mg(2+) at 2.0-A resolution. Elimination of a Mg(2+) ion induces significant conformational changes in the switch I region that opens up the nucleotide-binding site. Similar structural changes have been observed in the switch regions of Ha-Ras bound to its guanine nucleotide exchange factor, Sos. This RHOA-GDP structure reveals an important regulatory role for Mg(2+) and suggests that guanine nucleotide exchange factor may utilize this feature of switch I to produce an open conformation in GDP/GTP exchange.
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