What is it? As the name suggests, nonribosomal peptide synthesis (NRPS) generates polypeptides sans ribosome. The resultant peptides, generally short oligomers of two to perhaps 48 residues, are not genome-encoded.
Where ribosomal translation is limited to the standard complement of 20 L-amino acids, nonribosomal peptides may contain unusual building blocks, including D-amino acids, methylated variants of the standard amino acids, and nonproteinogenic, hydroxylated, and glycosylated residues; more than 300 precursors are currently known. Sometimes the peptide products are hetero-cyclized, and the peptide backbone may be branched.
How are the peptides made? Nonribosomal peptides are created on massive, assembly line-like synthetases. These enzymes are modular, comprising a series of functional units that can bind a naked amino acid, activate it as a thioester, and couple it to the growing peptide chain. In linear NRPSs, the sequence of modules acts as the template that defines the resulting peptide's sequence. But iterative and ...
