A GPR-Protein Interaction Surface of Giα:  Implications for the Mechanism of GDP-Release Inhibition

• Published in: Biochemistry (Easton) 2002-01, Vol.41 (1), p.258-265
• Main Authors: Natochin, Michael, Gasimov, Karim G, Artemyev, Nikolai O
• Format: Article
• Language: English
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi015708k

Proteins containing G-protein regulatory (GPR) motifs represent a novel family of guanine nucleotide dissociation inhibitors (GDIs) for Gα subunits from the Gi family. They selectively interact with the GDP-bound conformation of Giα and transducin-α (Gtα), but not with Gsα. A series of chimeric proteins between Giα1 and Gsα has been constructed to investigate GPR-contact sites on Gα subunits and the mechanism of GPR-protein GDI activity. Analysis of the interaction of two GPR-proteinsAGS3GPR and Pcp2with the chimeric Gα subunits demonstrated that the GPR−Giα1 interface involves the Giα1 switch regions and Giα1-144−151, a site within the helical domain. Residues within Giα1-144−151 form conformation-sensitive contacts with switch III, and may directly interact with a GPR-protein or form a GPR-binding surface jointly with switch III. The helical domain site is critical to the ability of GPR-proteins to act as GDIs. Our data suggest that a mechanism of the GDI activity of GPR-proteins is different from that of GDIs for monomeric GTPases and from the GDI-like activity of Gβγ subunits. The GPR-proteins are likely to block a GDP-escape route on Gα subunits.