Crystal structure and functional characterization of an Asp49 phospholipase A₂ from the bushmaster (Lachesis muta)

Snake-venom phospholipases A₂ (PLA₂s) are small, structurally conserved enzymes that contribute significantly to the pathophysiology of envenomation. Here, we report the purification and crystal structure of an Asp49-PLA₂ isolated from the venom of Lachesis muta, a pit viper from the Peruvian Amazon. The enzyme was purified using ion-exchange and size-exclusion chromatography and exhibited phospholipase activity in a dose- and time-dependent egg-yolk degradation assay. Pure protein crystals were obtained in space group P6₂22 and diffracted to 2.36 Å resolution, with two molecules in the asymmetric unit. The structure reveals the canonical fold of catalytically active group II PLA₂s, with a bound Ca²⁺ ion and a MES molecule in the active site of one monomer. Seven disulfide bonds stabilize the structure, although one bridge typically associated with the β-hairpin is absent and is replaced by a salt bridge as in other viperid PLA₂s. PISA analysis suggests a potential tetrameric assembly composed of two AB dimers generating an interface between two A subunits (A-A'). Electrostatic surface mapping reveals a notable positively charged channel at the A-A' interface, like that seen for a basic PLA₂ homodimer from Crotalus durissus terrificus in which the two active sites lie accessible to the membrane. This study presents the first structural and enzymatic analysis of an Asp49-PLA₂ from L. muta and provides insights into its oligomeric assembly, electrostatic landscape and potential adaptations relevant to its role in venom toxicity.