G beta subunit interacts with a peptide encoding region 956-982 of adenylyl cyclase 2 - Cross-linking of the peptide to free G beta gamma but not the heterotrimer

The region encoded by amino acids 956-982 of adenylyl cyclase 2 is important for G beta gamma stimulation. Interactions of a peptide encoding the 956-982 region of adenylyl cyclase 2 (QEHAQEPERQYMHIGTMVEFAYALVGK (QEHA peptide)) with G beta gamma subunits were studied, QEHA peptide was covalently attached to beta subunit of free G beta gamma by the cross-linker N-succinimidyl(4-iodoacetyl)aminobenzoate. Cross-linking was proportional to the amount of QEHA peptide added; other control peptides crosslinked minimally. When G(o) was used, very little crosslinking was observed with GDP and EDTA, but upon activation by guanosine 5'-3-O-(thio)triphosphate and Mg2+, specific cross-linking of the QEHA peptide to G beta was observed. We conclude that beta subunits of G proteins contain effector interaction domains that are occluded by G alpha subunits in the heterotrimer. Molecular modeling studies used to dock the QEHA peptide on to G beta indicate that amino acids 75-165 of G beta may be involved in effector interactions.