Phospholipase A 2 (PLA 2 ) is one of the representative toxic components of snake venom. PLA 2 s are categorized into several subgroups according to the amino acid at position 49, which comprises either Asp49, Lys49, Arg49 or Ser49. Previous studies suggested that the Lys49-PLA 2 assembles into an extremely stable dimer. Although the behavior on Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under reducing or non-reducing conditions suggested the presence of intermolecular disulfide bonds, these bonds were not observed in the crystal structure of Lys49-PLA 2 . The reason for this discrepancy between the crystal structure and SDS-PAGE of Lys49-PLA 2 remains unknown. In this study, we analyzed a Lys49-PLA 2 homologue from Protobothrops flavoviridis (PflLys49-PLA 2 BPII), by biophysical analyses including X-ray crystallography, SDS-PAGE, native-mass spectrometry, and analytical ultracentrifugation. The results demonstrated that PflLys49-PLA 2 BPII spontaneously oligomerized in the presence of SDS, which is one of the strongest protein denaturants.
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