Interactions of G(h)/transglutaminase with phospholipase C delta 1 and with GTP

The inositol phosphate hydrolyzing activity of human phospholipase C delta 1 (PLC delta 1) is markedly inhibited when the enzyme is coexpressed with t he human heart G(h)/transglutaminase (TG) in human embryonic kidney cells. Because the cotransfection does not affect the amount of PLC delta 1 in the cells, the depression of phospholipase activity probably is a result of a direct interaction between the two proteins. An ELISA procedure was employe d to document the associations of purified TC preparations from a variety o f tissues (human red cells, rabbit lens, guinea pig liver) with PLC delta 1 . Nucleotides (GTP > GDP > ATP > GMP = ADP, in order of decreasing efficien cy) interfered with the formation of the PLC delta 1:TG complex, A conforma tional change in the TG partner, occurring with nucleotide binding, is thou ght to be responsible for dissociating the two proteins. The structural rea rrangement produces a remarkable shift in the anodic mobility of TG in elec trophoresis: TG(slow) + GTP reversible arrow [TG:GTP](fast). Altogether, ou r findings indicate that GTP controls PLC delta 1 activity by releasing thi s protein from an inhibitory association with G(h)/transglutaminase.