A SequenceSpace analysis of Lys49 phopholipases A2: clues towards identification of residues involved in a novel mechanism of membrane damage and in myotoxicity

'SequenceSpace' analysis is a novel approach which has been used toidentify unique amino acids within a sub-family of phospholipases A2 (PLA2)in which the highly conserved active site residue Asp49 is substituted byLys (Lys49-PLA2s). Although Lys49-PLA2s do not bind the catalytic co-factorCa2+ and possess extremely low catalytic activity, they demonstrate aCa2+-independent membrane damaging activity through a poorly understoodmechanism, which does not involve lipid hydrolysis. Additionally,Lys49-PLA2s possess combined myotoxic, oedema forming and cardiotoxicpharmacological activities, however the structural basis of these variedfunctions is largely unknown. Using the 'SequenceSpace' analysis we haveidentified nine residues highly unique to the Lys49- PLA2 sub-family, whichare grouped in three amino acid clusters in the active site, hydrophobicsubstrate binding channel and homodimer interface regions. These threehighly specific residue clusters may have relevance for theCa2+-independent membrane damaging activity. Of a further 15 lessstringently conserved residues, nine are located in two additional clusterswhich are well isolated from the active site region. The less strictlyconserved clusters have been used in predictive sequence searches tocorrelate amino acid patterns in other venom PLA2s with theirpharmacological activities, and motifs for presynaptic and combinedtoxicities are proposed.