Characterizing the interactions between the two subunits of the p101/p110γ phosphoinositide 3-kinase and their role in the activation of this enzyme by Gβγ subunits

Recently, we have reported the purification and cloning of a novel G protein beta gamma subunit-activated phosphoinositide S-kinase from pig neutrophils. The enzyme comprises a p110 gamma catalytic subunit and a p101 regulatory subunit. Now we have cloned the human ortholog of p101 and generated panels of p101 and p110 gamma truncations and deletions and used these in in vitro and in vivo assays to determine the protein domains responsible for subunit interaction and activation by beta gamma subunits. Our results suggest large areas of p101 including both N- and C-terminal portions interact with the N-terminal half of p110 gamma, While modifications of the N terminus of p110 gamma could modulate its intrinsic catalytic activity, binding to the N-terminal region of p101 was found to be indispensable for activation of heterodimers with G(beta gamma).