Biochemical characterization, developmental expression, and induction of the immune protein scolexin from Manduca...

The immune protein, scolexin, a bacteria-induced, larva-specific protein from Manduca sexta, was shown to exist in the hemolymph in two isoelectric forms designated herein as scolexin-1 and scolexin-2 (native M(r) approximately 72 kd). These two charge isomers appeared to share the same amino acid composition. Scolexin is composed of two subunits (peptide M(r) approximately 36 kd) that possess the same N-terminus. Scolexin-2 was subjected to glycosyl composition analysis, revealing the presence of galactose, glucose, mannose, xylose, and sialic acid residues. Hybridization of epidermal RNA with oligonucleotides deduced from the scolexin N-terminal sequence showed a continuous decline in mRNA following day 0 of the 5th larval instar. By employing in vitro protein labelling, it was found that organ cultures of the epidermis from immune larvae showed a greater ability over that of naive epidermal cultures to synthesize scolexin; these data reflected the inducible response seen in the hemolymph, and confirm other data indicating that the epidermis is an important site of scolexin biosynthesis.