Download MendeleyStructures of active conformations of Gi alpha 1 and the mechanism of GTP hydrolysis.
Coleman, D.E., Berghuis, A.M., Lee, E., Linder, M.E., Gilman, A.G., Sprang, S.R.(1994) Science 265: 1405-1412
- PubMed: 8073283
- DOI: https://doi.org/10.1126/science.8073283
- Primary Citation of Related Structures:
1GFI, 1GIA, 1GIL - PubMed Abstract:
Mechanisms of guanosine triphosphate (GTP) hydrolysis by members of the G protein alpha subunit-p21ras superfamily of guanosine triphosphatases have been studied extensively but have not been well understood. High-resolution x-ray structures of the GTP gamma S and GDP.AlF4- complexes formed by the G protein Gi alpha 1 demonstrate specific roles in transition-state stabilization for two highly conserved residues. Glutamine204 (Gln61 in p21ras) stabilizes and orients the hydrolytic water in the trigonal-bipyramidal transition state. Arginine 178 stabilizes the negative charge at the equatorial oxygen atoms of the pentacoordinate phosphate intermediate. Conserved only in the G alpha family, this residue may account for the higher hydrolytic rate of G alpha proteins relative to those of the p21ras family members. The fold of Gi alpha 1 differs from that of the homologous Gt alpha subunit in the conformation of a helix-loop sequence located in the alpha-helical domain that is characteristic of these proteins; this site may participate in effector binding. The amino-terminal 33 residues are disordered in GTP gamma S-Gi alpha 1, suggesting a mechanism that may promote release of the beta gamma subunit complex when the alpha subunit is activated by GTP.
Organizational Affiliation:
Howard Hughes Medical Institute, Dallas, TX.
