Gβ subunit interacts with a peptide encoding region 956-982 of adenylyl cyclase 2. Cross-linking of the peptide to free Gβγ but not the heterotrimer

The region encoded by amino acids 956-982 of adenylyl cyclase 2 is important for Gβγ stimulation. Interactions of a peptide encoding the 956- 982 region of adenylyl cyclase 2 (QEHAQEPERQYMHIGTMVEFAYALVGK (QEHA peptide)) with Gβγ subunits were studied. QEHA peptide was covalently attached to β subunit of free Gβγ by the cross-linker N-succinimidyl(4-iodoacetyl)amino- benzoate. 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 Mg ²⁺, specific cross-linking of the QEHA peptide to Gβ was observed. We conclude that β subunits of G proteins contain effector interaction domains that are occluded by Gα subunits in the heterotrimer. Molecular modeling studies used to dock the QEHA peptide on to Gβ indicate that amino acids 75-165 of Gβ may be involved in effector interactions.