Structural elements of Trimeresurus flavoviridis serum inhibitors for recognition of its venom phospholipase A2 isozymes

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Abstract
Five inhibitors (PLI‐I–V) against Trimeresurus flavoviridis (Tf, habu snake, Crotalinae) venom phospholipase A2 (PLA2) isozymes have been isolated from its serum. PLI‐I, which is composed of two repeated three‐finger motifs, and PLI‐IV and PLI‐V, which contain a sequence similar to the carbohydrate recognition domain (CRD) of C‐type lectins, were expressed in the forms fused with glutathione S‐transferase (GST). The resulting GST‐PLIs showed ability to bind to three Tf venom PLA2 isozymes. The binding study with the truncated forms indicated that one of two three‐finger motifs of PLI‐I was able to bind to PLA2 isozymes. The N‐terminal 37‐amino acid fragment and the CRD‐like domain of PLI‐IV and PLI‐V were bound to PLA2 isozymes. On the other hand, their C‐terminal 12‐amino acid segment also associated with PLA2 isozymes. When either of two units of a hydrophobic tripeptide in this sequence was replaced by trialanine, the binding was completely abolished, indicating that the C‐terminal hydrophobic cores of PLI‐IV and PLI‐V were critically responsible for the binding to venom PLA2 isozymes.

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