CRYSTAL-STRUCTURE OF THE C2 DOMAIN FROM PROTEIN-KINASE C-DELTA

Background: The protein kinase C (PKC) family of lipid-dependent serin e/threonine kinases plays a central role in many intracellular eukaryo tic signalling events, Members of the novel (delta, epsilon, eta, thet a) subclass of PKC isotypes lack the Ca2+ dependence of the convention al PKC isotypes and have an N-terminal C2 domain, originally defined a s V0 (variable domain zero). Biochemical data suggest that this domain serves to translocate novel PKC family members to the plasma membrane and may influence binding of PKC activators. Results: The crystal str ucture of PKC-delta C2 domain indicates an unusual variant of the C2 f old. Structural elements unique to this C2 domain include a helix and a protruding beta hairpin which may contribute basic sequences to a me mbrane-interaction site. The invariant C2 motif, Pro-X-Trp, where X is any amino acid, forms a short crossover loop, departing radically fro m its conformation in other C2 structures, and contains a tyrosine pho sphorylation site unique to PKC-delta. This loop and two others adopt quite different conformations from the equivalent Ca2+-binding loops o f phospholipase C-delta and synaptotagmin I, and lack sequences necess ary for Ca2+ coordination. Conclusions: The N-terminal sequence of Ca2 +-independent novel PKCs defines a divergent example of a C2 structure similar to that of phospholipase C-delta. The Ca2+-independent regula tion of novel PKCs is explained by major structural and sequence diffe rences resulting in three non-functional Ca2+-binding loops. The obser ved structural variation and position of a tyrosine-phosphorylation si te suggest the existence of distinct subclasses of C2-like domains whi ch may have evolved distinct functional roles and mechanisms to intera ct with lipid membranes.