The influence of deletion mutations on phospholipase C-gamma 1 activity

Phospholipase C-gamma l, a substrate for many growth factor receptor and no nreceptor tyrosine kinases, produces second messenger molecules that are el ements of signal transduction pathways related to cell proliferation. The i nfluence of deletion mutations, which do not intrude on the domains require d for catalytic function, on the basal activity of this enzyme is reported. Removal of the first 74 amino-terminal residues increases phospholipase C activity, while deletion of the carboxy-terminal 81 residues decreases enzy me activity. Deletion of the SH3-SH2-SH3 central region, which separates th e two domains (X, Y) responsible. for catalytic function, also increases en zymatic activity. Interestingly, addition of a recombinant SH2-SH2-SH3 frag ment of phospholipase C-gamma 1 to the holoenzyme inhibits its phospholipas e activity at pH 7.0, but not at pH 5.0. However, addition of individual SH 2 or SH3 domains does not influence activity of the holoenzyme. All three d eletion mutants, in contrast to the holoenzyme, are relatively resistant to V8 proteolysis and activation induced by the epidermal growth factor recep tor tyrosine kinase, which require, respectively, specific proteolysis and phosphorylation sites within the SH region. This suggests a conformational change is induced in the SH region by deletion at either the amino- or carb oxy-termirnus. (C) 1999 Academic Press.