ISOLATION AND CHARACTERIZATION OF THE LANTIBIOTIC SALIVARICIN-A AND ITS STRUCTURAL GENE SALA FROM STREPTOCOCCUS-SALIVARIUS 20P3

A bacteriocin-like inhibitory substance, salivaricin A, was purified f rom cultures of Streptococcus salivarius 20P3 and was shown by ion spr ay mass spectrometry to have a molecular mass of 2,315 +/- 1.1 Da. Ami no acid composition analysis demonstrated the presence of lanthionine, indicating that salivaricin A may be a member of the lantibiotic clas s of antibiotic substances. The sequence of eight amino acids at the N terminus of the molecule was determined by Edman degradation, and mix ed oligonucleotide probes based on part of this sequence (GSGWLA) were used to detect the salivaricin A structural gene. A 6.2-kb EcoRI frag ment of chromosomal DNA from strain 20P3 that hybridized with the prob es was cloned, and the hybridizing region was further localized to a 3 79-bp DraI-AluI fragment. Analysis of the nucleotide sequence of this fragment indicated that salivaricin A is synthesized as a 51-amino-aci d prepeptide that is posttranslationally modified and cleaved to give a biologically active 22-residue peptide containing one lanthionine an d two beta-methyllanthionine residues. The secondary structure of pres alivaricin A was predicted to be similar to that of type A lantibiotic s, with a hydrophilic alpha-helical leader sequence and a propeptide r egion with potential for beta-turn formation and a lack of alpha-helic ity. The sequence around the cleavage site of presalivaricin A differe d from that of other type A lantibiotics but was similar to that of se veral bacteriocin-like inhibitory substances produced by lactic acid b acteria.