Structure investigation of Maltacine C1a, C1b, C2a and C2b—cyclic peptide lactones of the Maltacine complex from Bacillus subtilis

Abstract

A new complex of cyclic peptide lactone antibiotics from Bacillus subtilis, which we named Maltacines, has recently been described. The structure elucidation of four of them is reported in this paper. The amino acid sequences and structures of the peptides were found by MS(n) of the ring-opened linear peptides, which gave uninterrupted sequences of Bn and Y''n ions. The identities of three unknown residues in the sequences were solved by a combination of derivatisation with phenylisothiocyanate (PITC), high-resolution mass spectrometry and H/D exchange. The nature and position of the cyclic structure was disclosed by a chemo-selective ring opening with Na18OH and was found to be a lactone formed between a hydroxyl of residue number 4 and the C-terminal amino acid number 12. For verification of the structure of the B2+ ion, peptides with different combinations of P/Q and P/K at the N-terminus were synthesised. The structure of the four peptides were found to be: C1a and C2a: cyclo-4,12(P-Q-Y-Adip-V-E-T-Y-Orn-103-Y-I-OH) and C1b/C2b: cyclo-4,12(P-Q-Y-Adip-V-E-T-Y-K-103-Y-I-OH). Adip = aminodihydroxy pentanoic acid.

Lipopeptides Produced by a Soil Bacillus Megaterium Strain

“…The information from the well-studied species Bacillus subtilis, shows a great plasticity in producing antibiotic substances. Among them, cyclic lipopeptides and cyclic peptides such as maltacins [20][21][22][23] were identified. The inspection of the amino acidic portion of these substances indicates that all are versions of a central theme, although their activities both "in vivo" and "in vitro" may be different.…”

Use of synthetic analogues in confirmation of structure of the peptide antibiotics Maltacines

“…6). All five spectra are almost identical, showing loss of NH 3 native D1c and E1b than in Fengycin IX, where it is of very low abundance.…”

“…The extra peptide of one higher unit mass was formed during the ring-opening reaction with NaOH and caused a de-amidation of glutamine to glutamic acid [2][3][4][5]. The combined isotopic clusters for these two peptides cause the A + 1 isotope in the B n ion series to become the most abundant.…”

“…The potential applied to the nano-flow tip was 0.8-1 kV. The collision energies for the CID experiments were the same as those used earlier in the studies of the native Maltacines [2][3][4][5] ( Table 1).…”

“…The Maltacines comprise a family of peptide lactone antibiotics produced by a strain of Bacillus subtilis [1] of which 13 of the molecules have been studied [1][2][3][4][5]. The Maltacines are previously suggested by the author to be cyclo-4,12 peptide lactones where the members have major parts of their primary sequences in common.…”