A SEQUENCESPACE ANALYSIS OF LYS49 PHOSPHOLIPASES A(2) - CLUES TOWARDSIDENTIFICATION OF RESIDUES INVOLVED IN A NOVEL MECHANISM OF MEMBRANE DAMAGE AND IN MYOTOXICITY

'SequenceSpace' analysis is a novel approach which has been used to id entify unique amino acids within a subfamily of phospholipases A(2) (P LA(2)) in which the highly conserved active site residue Asp49 is subs tituted by Lys (Lys49-PLA(2)s). Although Lys49-PLA(2)s do not bind the catalytic co-factor Ca2+ and possess extremely low catalytic activity , they demonstrate a Ca2+-independent membrane damaging activity throu gh a poorly understood mechanism, which does not involve lipid hydroly sis. Additionally, Lys49-PLA(2)s possess combined myotoxic, oedema for ming and cardiotoxic pharmacological activities, however the structura l basis of these varied functions is largely unknown. Using the 'Seque nceSpace' analysis we have identified nine residues highly unique to t he Lys49-PLA(2) sub-family, which are grouped in three amino acid clus ters in the active site, hydrophobic substrate binding channel and hom odimer interface regions. These three highly specific residue clusters may have relevance for the Ca2+-independent membrane damaging activit y. Of a further 15 less stringently conserved residues, nine are locat ed in two additional clusters which are well isolated from the active site region, The less strictly conserved clusters have been used in pr edictive sequence searches to correlate amino acid patterns in other v enom PLA(2)s with their pharmacological activities, and moths for pres ynaptic and combined toxicities are proposed.