Structural and Functional Properties of Cr 5, a New Lys49 Phospholipase A2 Homologue Isolated from the Venom of the Snake Calloselasma rhodostoma

Cr 5 PLA₂ homologous (K49) was isolated from Calloselasma rhodostoma venom in only one chromatographic step in reverse phase HPLC (RP-HPLC) (on μ-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 PLA₂. The complete amino acid sequence of Cr 5 PLA₂ contains 120 residues, resulting in a calculated pI value of 5.55. This sequence shows high identity values when compared to other K49 PLA₂s isolated from the venoms of viperid snakes. Lower identity is observed in comparison to D49 PLA₂s. 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 LD₅₀ 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 PLA₂ and the combined structural and functional information obtained classify Cr 5 as a new member of the K49 PLA₂ family, since it presents typical features from such proteins.