Phospholipases A2 from Callosellasma rhodostoma venom gland cloning and sequencing of 10 of the cDNAs, three-dimensional modelling and chemical modification of the major isozyme.
Callosellasma rhodostoma (Malayan pitviper) is a monotypic Asian pitviper of medical importance. Three acidic phospholipases A2 (PLA2s) and one basic PLA2-homolog were purified from its venom while 10 cDNAs encoding distinct PLA2s were cloned from venom glands of a Thailand specimen of this species. Complete amino-acid sequences of the purified PLA2s were successfully deduced from their cDNA sequences. Among the six un-translated PLA2 cDNAs, two apparently result from recombination of its Lys49-PLA2 gene with its Asp49-PLA2 genes. The acidic PLA2s inhibit platelet-aggregation, while the noncatalytic PLA2-homolog induces local edema. This basic PLA2-homolog contains both Asp49 and other, unusual substitutions unique for the venom Lys49-PLA2 subtype (e.g. Leu5, Trp6, Asn28 and Arg34). Three-dimensional modelling of the basic protein revealed a heparin-binding region, and an abnormal calcium-binding pocket, which may explain its low catalytic activity. Oxidation of up to six of its Met residues or coinjection with heparin reduced its edema-inducing activity but methylation of its active site His48 did not. The distinct Arg/Lys-rich and Met-rich region at positions 10-36 of the PLA2 homolog presumably are involved in its heparin-binding and the cell membrane-interference leading to edema and myotoxicity.
Tsai
I H
IH
Institute of Biological Chemistry, Academia Sinica, Taipei, Taiwan. bc201@gate.sinica.edu.tw
Wang
Y M
YM
Au
L C
LC
Ko
T P
TP
Chen
Y H
YH
Chu
Y F
YF
D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D003435:Crotalid Venoms / Q000737:chemistry / Q000633:toxicity; D018076:DNA, Complementary; D004487:Edema / Q000139:chemically induced; D005260:Female; D007527:Isoenzymes / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010741:Phospholipases A / Q000737:chemistry* / Q000378:metabolism* / Q000633:toxicity; D054467:Phospholipases A2; D011487:Protein Conformation; D051381:Rats; D017208:Rats, Wistar; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D017841:Trimeresurus
D003435:Crotalid Venoms; D018076:DNA, Complementary; D007527:Isoenzymes; D010741:Phospholipases A; D054467:Phospholipases A2