SDS-induced oligomerization of Lys49-phospholipase A(2) from snake venom

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.