Structural and functional properties of Cr 5, a new Lys49 phospholipase A2 homologue isolated from the venom of the snake Calloselasma rhodostoma.

Cr 5 PLA(2) homologous (K49) was isolated from Calloselasma rhodostoma venom in only one chromatographic step in reverse phase HPLC (RP-HPLC) (on mu-Bondapack C-18). A molecular mass of 13.965 Da was determined by MALDI-TOF mass spectrometry. The amino acid composition showed that Cr 5 had a high content of Lys, Tyr, Gly, Pro, and 14 half-Cys residues, typical residues of a basic PLA(2). The complete amino acid sequence of Cr 5 PLA(2) contains 120 residues, resulting in a calculated pI value of 5.55. This sequence shows high identity values when compared to other K49 PLA(2)s isolated from the venoms of viperid snakes. Lower identity is observed in comparison to D49 PLA(2)s. The sequence found was SLVELGKMIL QETGKNPAKS YGAYGCNCGV LGRHKPKDAT DRCCFVHKCC YKKLTGCDPK KDRYSYSWKD KTIVCGENNP CLKEMCECDK AVAICLRENL DTYNKKYRYL KPFCKKADDC. In mice, Cr 5 induced myonecrosis and edema upon intramuscular and intravenous injections, respectively. The LD(50) of Cr 5 was 0.070 mg/kg of the animal weight, by intracerebroventricular (i.c.v.) route. In vitro, the toxin caused rapid cytolytic effect upon mouse skeletal muscle myoblasts in culture. The isolation of this PLA(2) and the combined structural and functional information obtained classify Cr 5 as a new member of the K49 PLA(2) family, since it presents typical features from such proteins.