Streptogramin B

Streptogramin B is a subgroup of the streptogramin antibiotics family. These natural products are cyclic hexa- or hepta depsipeptides produced by various members of the genus of bacteria Streptomyces. Many of the members of the streptogramins reported in the literature have the same structure and different names; for example, pristinamycin IA = vernamycin Bα = mikamycin B = osteogrycin B.

The biosynthesis of streptogramin B is carried out by large multifunctional enzymes called non-ribosomal peptide synthetases (NRPS). In the NRPS system, each amino acid is activated as an aminoacyladenylate and is linked to the enzyme as a thioester with a phosphopantetheinyl group. An elongation reaction then occurs by transferring the activated carboxyl to the amino group in the next amino acid, thus executing the N-to-C stepwise condensation.

NRPSs contain several modules on a single polypeptide. Each of these modules can catalyze activation, condensation and a modification reaction specific to one kind of amino acid. A typical elongation module consists of an adenylation domain (A), a peptidyl carrier protein domain (PCP) and a condensation domain (C). Some other domains may be present that are responsible for modifications to the residues, such as epimerization domain (E) and N-methyltransferase domain (MT). The domain responsible for the termination is the thioesterase domain (TE) located in the final module.

The general amino acid composition of streptogramin B consists of: 3-hydroxypicolinic acid, L-threonine, D-aminobutyric acid, L-proline, 4-N,N-(dimethylamino)-L-phenylalanine, 4-oxo-L-pipecolic acid and phenylglycine.

...
Wikipedia