1git

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spinqualitylabelsall models 1git, resolution 2.60Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

STRUCTURE OF GTP-BINDING PROTEIN

Overview

BACKGROUND: G proteins play a vital role in transmembrane signalling, events. In their inactive form G proteins exist as heterotrimers, consisting of an alpha subunit, complexed with GDP and a dimer of, betagamma subunits. Upon stimulation by receptors, G protein alpha, subunits exchange GDP for GTP and dissociate from betagamma . Thus, activated, alphasubunits stimulate or inhibit downstream effectors. The, duration of the activated state corresponds to the single turnover rate of, GTP hydrolysis, which is typically in the range of seconds. In Gialpha1, the Gly203-->Ala mutation reduces the affinity of the substrate for Mg2+, inhibits a key conformational step that occurs upon GTP binding and, consequently inhibits the release of betagamma subunits from the GTP, complex. The structure of the Gly203-->Ala mutant of Gialpha1, (G203AGialpha1) bound to the slowly hydrolyzing analog of GTP (GTPgammaS), has been determined in order to elucidate the structural changes that take, place during hydrolysis. RESULTS: We have determined the three dimensional, structure of a Gly203-->Ala mutant of Gialpha1 at 2.6 A resolution., Although crystals were grown in the presence of GTPgammaS and Mg2+, the, catalytic site contains a molecule of GDP and a phosphate ion, but no, Mg2+. The phosphate ion is bound to a site near that occupied by the, gamma-phosphate of GTPgammaS in the activated wild-type alpha subunit. A, region of the protein, termed the Switch II helix, twists and bends to, adopt a conformation that is radically different from that observed in, other Gialpha1 subunit complexes. CONCLUSIONS: Under the conditions of, crystallization, the Gly203-->Ala mutation appears to stabilize a, conformation that may be similar, although perhaps not identical, to the, transient ternary product complex of Gialpha1-catalyzed GTP hydrolysis., The rearrangement of the Switch II helix avoids a potential steric, conflict caused by the mutation. However, it appears that dissociation of, the gamma-phosphate from the pentacoordinate intermediate also requires a, conformational change in Switch II. Thus, a conformational rearrangement, of the Switch II helix may be required in Galpha-catalyzed GTP hydrolysis.

About this Structure

1GIT is a Single protein structure of sequence from Rattus norvegicus with PO4 and GDP as ligands. Full crystallographic information is available from OCA.

Reference

Structure of the GDP-Pi complex of Gly203-->Ala gialpha1: a mimic of the ternary product complex of galpha-catalyzed GTP hydrolysis., Berghuis AM, Lee E, Raw AS, Gilman AG, Sprang SR, Structure. 1996 Nov 15;4(11):1277-90. PMID:8939752

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