Isolation of amino acid activating subunit-pantetheine protein complexes: Their role in chain elongation in tyrocidine synthesis

Abstract

Dissociation of the multienzymes of tyrocidine synthesis by prolonged incubation of crude extracts of Bacillus brevis (Dubos strain, ATCC 8185) has yielded, on Sephadex G-100 chromatography, two fractions of amino acid activating subunits, a larger one of 70,000 daltons and a smaller one of 90,000 dalto s; the latter was a complex consisting of the 70,000 dalton subunit and the pantetheine-carrying protein of about 20,000 daltons. When it dissociated, the intermediate enzyme, which activates three amino acids, contained two-thirds of the subunits in the 70,000 dalton and one-third in the 90,000 dalton fraction; the heavy enzyme, which activates six amino acids, contained five-sixths of the subunits in the former fraction and one-sixth in the latter. Both fractions showed ATP-PP1 exchange with all amino acids that are activated by the respective polyenzymes. With proline as an example, the 70,000 dalton subunit exhibited a single low-affinity binding site, which should correspond to the peripheral thiol acceptor site, whereas the 90,000 dalton subunit showed both a low-affinity binding site and an additional high-affinity site for proline; the high-affinity site is attributed to the pantetheine present on the pantetheine-carrying protein, and suggests that amino acids are translocated from the peripheral SH to the pantetheine-carrying moiety during chain elongation. This was confirmed by the observation that the 90,000 dalton complex, when incubated with the light enzyme in the presence of phenylalanine and proline, produced DPhe-Pro dipeptide that cyclized into DPhe-Pro diketopiperazine, but the 70,000 dalton activating subunit, when similarly incubated, did not. After subunit dissociation, however, no further elongation occurred after the transfer from phenylalanine to proline.Various microorganisms have now been found to produce antibiotic peptides nonribosomally (1-18). Much of our present knowledge and our formulation (1) of nonribosomal peptide synthesis has been obtained from the study of the biosynthetic mechanisms of gramicidin S and tyrocidine, which are decapeptide antibiotics produced by the Bacillus brevis strains ATCC 9999 and ATCC 8185, respectively. The biosynthesis of gramicidin S requires two complementary enzymes, that of tyrocidine, three. Of these complementary enzymes, one for gramicidin S and two for tyrocidine biosynthesis are multienzymes containing pantetheine (7-13, 15). The peptide synthesis proceeds with the ATP-driven activation of amino acids followed by attachment of the activated amino acids to the peripheral enzymic thiol groups; then, with the aid of enzymelinked pantetheine, condensation of the thioesterified amino acids ensues (1,(7)(8)(9). Both the involvement of two or more enzymes, including the pantetheine-containing multienzymes, and the ATP-driven activation of amino acids now appear to be common features of the nonribosomal synthesis of many peptide antibiotics (4-6, 13-1]8).The three complementary enzymes of tyrocidine synthesis (9,12,16) acid activating subuni...

Peptide Bond Formation in Nonribosomal Peptide Biosynthesis

“…Although this reaction is probably noncatalytic, it is favored by the conformational stability (49) of the prolinecontaining diketopiperazine and allows a slow turnover of dipeptide formation. The same reaction has also been observed with proteolytic fragments probably corresponding to the first two modules of the wild-type enzymes (43,44). The tetramodular GrsB was treated with proteases, and a fragment with L-Pro-activating activity was isolated.…”

“…This fragment, which was shown to contain the authentic N terminus of GrsB, was estimated to be 114 kDa in size and accepted D-Phe from GrsA to form the D-Phe-L-Pro diketopiperazine (50). Likewise, a LPro-activating fragment of tyrocidine synthetase was obtained by prolonged incubation of crude cell extracts and upon incubation with TycA yielded the same product (44). Consistent with the similar initiation reaction, the corresponding modules in gramicidin S and tyrocidine synthesis are equivalently composed in terms of domain organization and share an especially high degree of sequence similarity (9,39,40,51).…”

“…Our assay is based on the similar initiation reaction of the gramicidin S and tyrocidine biosynthesis. For these systems, it was known that omission of the third amino acid in order of their synthesis leads to a premature cleavage of the D-Phe-L-Pro dipeptide intermediate (43,44). Although this reaction is probably noncatalytic, it is favored by the conformational stability (49) of the prolinecontaining diketopiperazine and allows a slow turnover of dipeptide formation.…”

“…The initiation reaction in both systems is the formation of the first peptide bond between D-Phe and L-Pro (42). Interestingly, in both cases, this dipeptide intermediate is cleaved off the enzyme template by intramolecular cyclization when the systems are not supplied with the substrate amino acid of the next module (43,44). In a reaction that is probably noncatalytic, the cyclic diketopiperazine (DKP; 3-benzyl-(8-ar)-hexahydro-pyrrolo[1,2-␣]pyrazine-1,4-dione) is formed by an intramolecular attack of the amino group of D-Phe on the thioesteractivated carboxyl of Pro.…”

Characterization of a Unique Glycosylated Anchor Endopeptidase That Cleaves the LPXTG Sequence Motif of Cell Surface Proteins of Gram-positive Bacteria

“…For example, tyrocidine, a cyclic decapeptide antibiotic from Bacillus brevis, contains ornithine and three phenylalanines, two of which are in the D-configuration. The mechanism of nonribosomal peptide synthesis was most extensively investigated previously in the synthesis of tyrocidine (67)(68)(69)(70). Recently, the genes encoding the polyenzymes of tyrocidine synthesis have been cloned (71).…”