1BOF

Crystal structures of the G protein Gi alpha 1 complexed with GDP and Mg2+: a crystallographic titration experiment.

(1998) Biochemistry 37: 14376-14385

• PubMed: 9772163 Search on PubMed
• DOI: https://doi.org/10.1021/bi9810306
• Primary Citation of Related Structures:  
  1BOF


• PubMed Abstract: 
  

  The effect of Mg2+ binding on the conformation of the inactive GDP-bound complex of the heterotrimeric G protein alpha subunit Gi alpha 1 has been investigated by X-ray crystallography. Crystal structures of the Gi alpha 1.GDP complex were determined after titration with 5, 10, 100, and 200 mM Mg2+. Comparison of these structures with that of the Mg2+-free complex revealed Mg2+ bound at the same site as observed in the structure of the active, Gi alpha 1. GTP gamma S.Mg2+-bound complex of Gi alpha 1, with a similar coordination scheme except for the substitution of a water molecule for an oxygen ligand of the gamma-phosphate of Gi alpha 1.GTP gamma S. Mg2+. In contrast to the GDP.Mg2+ complex of Gt alpha and of other G proteins, switch I residues of Gi alpha 1 participate in Mg2+ binding and undergo conformational changes as a consequence of Mg2+ binding. Partial order is induced in switch II, which is disordered in the Mg2+-free complex, but no order is observed in the switch III region. This contrasts with the GDP.Mg2+ complex of Gt alpha in which both switch II and III switch are ordered. Mg2+ binding also induces binding of an SO42- molecule to the active site in a manner which may mimic a Gi alpha 1.GDP.PO42-.Mg2+ product complex. Implications of these findings are discussed.

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Organizational Affiliation: 

Howard Hughes Medical Institute, Department of Biochemistry, The University of Texas Southwestern Medical Center, Dallas 75235-9050, USA.