One-Step Affinity Purification of Leucine-Rich α2-Glycoproteins from Snake Sera and Characterization of Their Phospholipase A2-Inhibitory Activities as β-Type Phospholipase A2 Inhibitors

Snakes contain three types of phospholipase A2 (PLA2)-inhibitory proteins in their blood, PLIα, β, and γ, which protect them from their own venom, PLA2. PLIβ is the snake ortholog of leucine-rich α2 glycoprotein (LRG). Since autologous cytochrome c (Cyt c) serves as an endogenous ligand for LRG, in this study, we purified snake LRGs from various snake serum samples using Cyt c affinity chromatography. All purified snake LRGs were found to be dimers linked by disulfide bonds. Laticauda semifasciata and Naja kaouthia LRGs showed no inhibitory activity against L. semifasciata PLA2 and weak inhibitory activity against Gloydius brevicauda basic PLA2. Elaphe climacophora PLIβ had weaker inhibitory activity against G. brevicauda basic PLA2 than G. brevicauda and Elaphe quadrivirgata PLIs, which are abundant in blood and known to neutralize G. brevicauda basic PLA2. Protobothrops flavoviridis LRG showed no inhibitory activity against basic venom PLA2, PL-X, or G. brevicauda basic PLA2. Binding analysis of P. flavoviridis LRG using surface plasmon resonance showed very strong binding to snake Cyt c, followed by that to horse Cyt c, weak binding to yeast Cyt c, and no binding to P. flavoviridis PL-X or BPI/II. We also deduced the amino acid sequences of L. semifasciata and P. flavoviridis LRG by means of cDNA sequencing and compared them with those of other known sequences of PLIs and LRGs. This study concluded that snake LRG can potentially inhibit basic PLA2, but, whether it actually functions as a PLA2-inhibitory protein, PLIβ, depends on the snake.