Subtilosin A is a bacteriocin from Bacillus subtilis.The protein has a cyclized peptide backbone and forms three cross-liks between the sulphurs of Cys13, Cys7 and Cys4 and the alpha-positions of Phe22,Thr28 and Phe31 [1].

1: Structure of subtilosin A, a cyclic antimicrobial peptide from Bacillus subtilis with unusual sulfur to alpha-carbon cross-links: formation and reduction of alpha-thio-alpha-amino acid derivatives. Kawulka KE, Sprules T, Diaper CM, Whittal RM, McKay RT, Mercier P, Zuber P, Vederas JC; Biochemistry. 2004;43:3385-3395. PMID:15035610