Structure of subtilosin A, an antimicrobial peptide from Bacillus subtilis with unusual posttranslational modifications linking cysteine sulfurs to α-carbons of phenylalanine and threonine

The complete primary and three-dimensional solution structures of subtilosin A (1), a bacteriocin from Bacillus subtilis, were determined by multidimensional NMR studies on peptide produced using isotopically labeled [13C,15N]medium derived from Anabaena sp. grown on sodium [13C]bicarbonate and [15N]nitrate. Additional samples of 1 were also generated by separate incorporations of [U-13C,15N]phenylalanine and [U-13C,15N]threonine using otherwise unlabeled media. The results demonstrate that in addition to having a cyclized peptide backbone (N and C termini), three cross-links are formed between the sulfurs of Cys13, Cys7, and Cys4 and the α-positions of Phe22, Thr28, and Phe31, respectively. Such posttranslational linkage of a thiol to the α-carbon of an amino acid residue is very unusual in natural peptides or proteins. Subtilosin A (1) belongs to a new class of bacteriocins. Copyright © 2003 American Chemical Society.