BIOCHEMICAL-CHARACTERIZATION AND PHARMACOLOGICAL PROPERTIES OF A PHOSPHOLIPASE A(2) MYOTOXIN INHIBITOR FROM THE PLASMA OF THE SNAKE BOTHROPS-ASPER

A protein that neutralizes the biological activities of basic phosphol ipase A(2) (PLA(2)) myotoxin isoforms from the venom of the snake Both rops asper was isolated from its brood by affinity chromatography with Sepharose-immobilized myotoxins. Biochemical characterization of this B. asper myotoxin inhibitor protein (BaMIP) indicated a subunit molec ular mass of 23-25 kDa, an isoelectric point of 4, and glycosylation. Gelfiltration studies revealed a molecular mass of 12O kDa, suggesting that BaMIP possesses an oligomeric structure composed of five 23-25kD a subunits. Functional studies indicated that BaMIP inhibits the PLA(2 ) activity of B. asper basic myotoxins I and III, as well as the myoto xicity and edema-forming activity in vivo and cytolytic activity in vi tro towards cultured endothelial cells, of all four myotoxin isoforms (I-IV) tested. Sequence analysis of the first 63 amino acid residues f rom the N-terminus of BaMIP indicated more than 65 % sequence similari ty to the PLA(2) inhibitors isolated from the blood of the crotalid sn akes Trimeresurus flavoviridis and Agkistrodon blomhoffii siniticus. T hese inhibitors also share sequences similar to the carbohydrate-recog nition domains of human and rabbit cellular PLA(2) receptors, suggesti ng a common domain evolution among snake plasma PLA(2) inhibitors and mammalian PLA(2) receptors. Despite this similarity, this is the first description of a natural anti-myotoxic factor from snake blood.