The complete amino acid sequence of staphylococcal enterotoxin C1

This report presents the complete amino acid sequence of staphylococcal enterotoxin C1. It has a total of 239 amino acids and a calculated Mr = 27,500. Reaction of the native toxin with trypsin produced five peptides, designated A through E. Their structures were determined after further fragmentation with cyanogen bromide, trypsin, and chymotrypsin. Overlap peptides were prepared by cleavage at the two half-cystine residues, and by the reaction of enterotoxin C1 with hydroxylamine. The latter procedure was employed when it was found that one of the three asparaginyl-glycine loci in the toxin is refractory to direct sequencing. The sequence is compared to staphylococcal enterotoxin B. Extensive homology is found, particularly in the carboxyl-terminal region. However, the segment spanned by the disulfide bond in enterotoxin C1 is three residues shorter than the corresponding segment in the B variant.