Thiol/disulfide exchange occurs in rotavirus structural proteins during contact with intestinal villus cell surface

Protein disulfide isomerase (PDI) is an enzyme that catalyzes disulfide bond reduction or formation and rearrangements of disulfide bridges, and also functions as a chaperone. During entry of some of the viruses PDI participates in thiol-disulfide exchange. Previous reports show that rotavirus entry is interfered by impermeant thiol/disulfide exchange inhibitors and antibodies against PDI. Our objective was to assess the interaction between PDI and triple-layered particles (TLPs) from rotavirus strains ECwt and RRV and from a human rotavirus isolate (HI) during the early steps of virus entry in a system of isolated small intestinal villi. Purified soluble PDI was incubated with either isolated intestinal villi or cell membrane-enriched fractions in the presence or absence of thiol/disulfide inhibitors such as bacitracin, DTNB or N- ethylmaleimide followed by the assessment of the PDI interactions with TLPs and rotavirus structural proteins in terms of their redox state changes. Soluble and membrane-bound PDI was found to interact with TLPs from all the rotaviruses assayed and also with the isolated structural proteins represented by the recombinant rVP5* (a tryptic cleavage product of VP4), rVP6 and the native VP7. PDI interaction with TLPs and rotavirus structural proteins was decreased by the presence of thiol/disulfide exchange inhibitors. Interactions of cell membrane-enriched fractions with TLPs produced rearrangements in the disulfide bridges of rotavirus structural proteins. We conclude that PDI interacts with rotavirus virions through redox reactions that could facilitate the rotavirus entry into the host cell. Keywords: cell surface PDI; thiol-disulfide exchange; rotavirus TLPs; virus entry; bacitracin; DTNB.