Pj. Belshaw et al., Aminoacyl-CoAs as probes of condensation domain selectivity in nonribosomal peptide synthesis, SCIENCE, 284(5413), 1999, pp. 486-489
In nonribosomal biosynthesis of peptide antibiotics by multimodular synthet
ases, amino acid monomers are activated by the adenylation domains of the s
ynthetase and loaded onto the adjacent carrier protein domains as thioester
s, then the formation of peptide bonds and translocation of the growing cha
in are effected by the synthetase's condensation domains. Whether the conde
nsation domains have any editing function has been unknown. Synthesis of am
inoacyl-coenzyme A (CoA) molecules and direct enzymatic transfer of aminoac
yl-phosphopantetheine to the carrier domains allow the adenylation domain e
diting function to be bypassed. This method was used to demonstrate that th
e first condensation domain of tyrocidine synthetase shows low selectivity
at the donor residue (D-phenylalanine) and higher selectivity at the accept
or residue (L-proline) in the formation of the chain-initiating D-Phe-L-Pro
dipeptidyl-enzyme intermediate.