1svk

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spinqualitylabelsall models 1svk, resolution 2.00Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

Structure of the K180P mutant of Gi alpha subunit bound to AlF4 and GDP

Overview

Heterotrimeric G protein alpha (G alpha) subunits possess intrinsic GTPase, activity that leads to functional deactivation with a rate constant of, approximately 2 min(-1) at 30 degrees C. GTP hydrolysis causes, conformational changes in three regions of G alpha, including Switch I and, Switch II. Mutation of G202-->A in Switch II of G alpha(i1) accelerates, the rates of both GTP hydrolysis and conformational change, which is, measured by the loss of fluorescence from Trp-211 in Switch II. Mutation, of K180-->P in Switch I increases the rate of conformational change but, decreases the GTPase rate, which causes transient but substantial, accumulation of a low-fluorescence G alpha(i1).GTP species. Isothermal, titration calorimetric analysis of the binding of (G202A)G alpha(i1) and, (K180P)G alpha(i1) to the GTPase-activating protein RGS4 indicates that, the G202A mutation stabilizes the pretransition state-like conformation of, G alpha(i1) that is mimicked by the complex of G alpha(i1) with GDP and, magnesium fluoroaluminate, whereas the K180P mutation destabilizes this, state. The crystal structures of (K180P)G alpha(i1) bound to a slowly, hydrolyzable GTP analog, and the GDP.magnesium fluoroaluminate complex, provide evidence that the Mg(2+) binding site is destabilized and that, Switch I is torsionally restrained by the K180P mutation. The data are, consistent with a catalytic mechanism for G alpha in which major, conformational transitions in Switch I and Switch II are obligate events, that precede the bond-breaking step in GTP hydrolysis. In (K180P)G, alpha(i1), the two events are decoupled kinetically, whereas in the native, protein they are concerted.

About this Structure

1SVK is a Single protein structure of sequence from Rattus norvegicus with MG, ALF and GDP as ligands. Active as Heterotrimeric G-protein GTPase, with EC number 3.6.5.1 Full crystallographic information is available from OCA.

Reference

Uncoupling conformational change from GTP hydrolysis in a heterotrimeric G protein alpha-subunit., Thomas CJ, Du X, Li P, Wang Y, Ross EM, Sprang SR, Proc Natl Acad Sci U S A. 2004 May 18;101(20):7560-5. Epub 2004 May 5. PMID:15128951

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