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![[Figure 1]](mh5117fig1mag.jpg)
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Figure 1
Tyrocidine A biosynthesis and mechanism of the epimerization reaction. (a) Schematic depiction of the tyrocidine biosynthesis cluster consisting of three distinct enzymes: TycA, TycB and TycC. In analogous NRP biosynthesis clusters comprising more than one polypeptide, epimerization domains are usually located at the C-termini of the synthetases to mediate mutual recognition with the succeeding synthetase. (b) Reaction mechanism of epimerization domains as postulated by Stachelhaus & Walsh (2000  ). After ATP-dependent activation of the incoming substrate L-Phe and subsequent transesterification onto the 4′-phosphopantetheine cofactor of the PCP domain, the Cα proton is abstracted by the epimerization domain. The resulting resonance-stabilized enolate intermediate is then reprotonated to give a mixture of L-Phe and D-Phe. (c) Structure of the peptide antibiotic tyrocidine. The cyclic decapeptide adopts a β-hairpin-like structure and contains two residues in the D-configuration: D-Phe 1 and D-Phe 4. |
![[Figure 1]](mh5117fig1.jpg)
 | STRUCTURAL BIOLOGY |
ISSN: 2059-7983
