Heparin binding to cobra basic phospholipase A(2) depends on heparin chainlength and amino acid specificity

Heparin is shown to bind specifically to the carboxyterminal region of toxi c type I phospholipase A(2) from Naja nigricollis (N-PLA(2)) by competition assay using synthetic polypeptides and heparin affinity chromatography. Th e binding strength is seen to depend on heparin chain length and the presen ce of N-sulfate groups of heparin. It is observed that both electrostatic a nd non-electrostatic interactions are involved in the specific binding of h eparin to the carboxy-terminus. When heparin's size is at least a decasacch aride, about two molecules of N-PLA(2) bind to one molecule of heparin, as evidenced by the chemical estimate of protein to carbohydrate ratio in such N-PLA(2)/heparin complexes. Based on such a stoichiometric measurement and computer modeling of the N-PLA(2)/heparin complex, it is suggested that th e binding sites of the two N-PLA(2) molecules on one heparin molecule lie o n the opposite sides of the heparin chain. (C) 1999 Federation of European Biochemical Societies.