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The crystal structure of the fast exchange mutant I56C/Q333C in Gα i1 suggests a mechanism for receptor‐mediated allosteric nucleotide exchange
Author(s) -
Funk Michael A,
Oldham William M,
Preininger Anita M,
Hamm Heidi E,
Iverson Tina M
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.5.a613
Subject(s) - allosteric regulation , heterotrimeric g protein , nucleotide , mutant , chemistry , protein structure , stereochemistry , biophysics , receptor , g protein , biochemistry , biology , gene
Heterotrimeric G protein signaling depends upon receptor‐induced nucleotide exchange in Gα. Recent data indicates that the C‐terminal α5 helix of Gα mediates this nucleotide exchange through an allosteric mechanism. We have designed a mutant, I56C/Q333C, in Gα i1 that should constrain the C‐terminus of the protein with a disulfide bond 10 Å away from the closest nucleotide‐interacting residue. The mutant Gα exhibits an elevated nucleotide exchange rate similar to that expected for an on‐pathway intermediate in the receptor‐catalyzed activation process. To investigate the mechanism of allosteric nucleotide exchange in Gα, the crystal structure of the I56C/Q333C mutant was determined to a resolution of 2.9 Å. The GDP·AlF 4 − structure verifies the presence of a disulfide bond which shifts the C‐terminal α5 helix. Despite limited changes in the nucleotide pocket between the mutant and wildtype structures, there are unique conformations observed in the switch regions and in the α4‐β6 and α2‐β4 loops. These structural data may provide new insight into the process of nucleotide exchange in Gα and the physical forces involved in the allosteric mechanism of receptor‐mediated nucleotide exchange.