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 imp ortant for G beta gamma stimulation. Interactions of a peptide encodin g the 956-982 region of adenylyl cyclase 2 (QEHAQEPERQYMHIGTMVEFAYALVG K (QEHA peptide)) with G beta gamma subunits were studied, QEHA peptid e 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 pe ptides crosslinked minimally. When G(o) was used, very little crosslin king 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 p roteins contain effector interaction domains that are occluded by G al pha subunits in the heterotrimer. Molecular modeling studies used to d ock the QEHA peptide on to G beta indicate that amino acids 75-165 of G beta may be involved in effector interactions.