EFFECT OF GAMMA-SUBUNIT CARBOXYL METHYLATION ON THE INTERACTION OF G-PROTEIN ALPHA-SUBUNITS WITH BETA-GAMMA-SUBUNITS OF DEFINED COMPOSITION

A baculovirus expression system was used to determine the contribution of carboxyl methylation of specific G protein gamma subunits to the i nteraction between alpha and beta gamma subunits. beta gamma subunits were carboxyl methylated by a membrane bound methyltransferase in Sf9 cells, and periodate oxidized adenosine inhibited this methylation by 90%. Carboxyl methylation of beta(1) gamma(2), beta(2) gamma(3), and b eta(2) gamma(7) enhanced pertussis toxin catalyzed ADP-ribosylation of alpha(i2) and alpha(i3) by about 2-fold. On the other hand, methylati on did not enhance membrane attachment of beta gamma subunits. These r esults suggest that methylation of isoprenylated gamma subunits is req uired for optimal G protein-mediated signal transduction, but not memb rane attachment. (C) 1998 Elsevier Science Inc.