The plasma protein scolexin from Manduca sexta is induced by baculovirus infection and other immune challenges

Manduca sexta larvae infected per os with a sublethal dose of Erinnyis ello granulosis virus (EeGV) contain an induced plasma protein of ca 33-36 kDa [Finnerty et al. (1994) J. Invertebr. Pathol. 63, 140-144]. This virus-induced protein shares characteristics with scolexin, a bacteria-induced plasma protein from M. sexta, so in this study we compared the two proteins. Two-dimensional gel electrophoresis reveals the induction of polypeptides corresponding to the subunits of scolexin in the plasma from EeGV-infected, as well as bacteria-injected, larvae. Immunoblots of these two-dimensional polyacrylamide gels show that antiserum against the virus-induced protein cross-reacts with the putative scolexin polypeptides induced by either EeGV infection or bacteria injection. Amino acid analysis of the virus-induced protein shows it to be very similar to scolexin, and the N-terminal sequences of the two proteins are nearly identical. From these data, we conclude that the virus-induced protein and scolexin are identical, or at least isoforms of the same protein. Using immunoblot, we also demonstrate that scolexin is induced in M. sexta plasma by injection with yeast or lipopolysaccharide from Serratia marcescens.