Heterodimeric vipoxin and its individual monomeric subunits display a dynamic structure-function relationship on RPE...

Known as some of the most toxic venom components, snake venom Phospholipases A₂ (svPLA₂) impress with their great arsenal of activities, based on catalytic specificity and a variety of non-catalytic "pharmacological" effects using complex molecular mechanisms that can affect different tissues and organs. Here, we aim to reveal the role of the intricate interactions between the monomeric subunits of the heterodimeric neurotoxic complex vipoxin in order to perform multiple differentiated and regulated biological activities in RPE cells. Vipoxin, isolated from the venom of Vipera ammodytes ssp. meridionalis, is composed of a basic and toxic secreted PLA₂ enzyme subunit (GIIA sPLA₂, vipoxin basic component, VBC) and an acidic, enzymatically inactive and non-toxic subunit (vipoxin acidic component, VAC). We established that vipoxin and its separated monomeric subunits affect integrity and viability of the cells of two RPE lines using a combination of catalytic and non-catalyticmechanisms. Individual monomeric subunits VBC and VAC induce cytotoxicity, cytoskeletal rearrangements, affect transepithelial resistance and cell monolayer integrity, trigger apoptosis, p38 MAPK signaling pathway and genotoxicity, provoking very elaborate cellular response in both cell lines. VBC uses its catalytic and pharmacological activities more pronounced in RPE-1 than in ARPE-19 cell line, triggering DNA double-strand damage as well as a higher degree of cytotoxicity (up to 45 %) in a concentration-dependent manner. In contrast, the non-catalyticVAC exhibited insignificant effect on the membrane integrity of both RPE cell lines but induced very high degree of DNA damage in ARPE-19 cells. Heterodimeric vipoxin displaced its complex and dynamic biological efficiency in both cell lines. In general, all the investigated activities of vipoxin and its individual monomeric subunits proved our assumption for the existence of complex dynamic conformational and structural interactions between the subunits providing an immediate selection of the enzymatic or "pharmacological" mode of action, strongly dependent on RPE cell membrane composition and their microenvironment.