The nonribosomal code refers to key amino acid residues and their positions within the primary sequence of an adenylation domain of a nonribosomal peptide synthetase used to predict substrate specificity and thus (partially) the final product.
Enzyme characterization by, for example, ATP-pyrophosphate exchange assays for substrate specificity, in silico substrate-binding pocket modelling and structure-function mutagenesis (in vitro tests or in silico modelling) helps support predictive algorithms.
The nonribosomal peptide synthetase (NRPS), a multi-modular enzyme complex, minimally contains repeating, tri-domains (adenylation (A), peptidyl carrier protein (PCP) and lastly condensation(C)).
NRPS, NRPS-like or NRPS-PKS complexes also exist and have domain variations, additions and/or exclusions.
[3] LTKVGHIG → Asp (Aspartic acid) VGEIGSID → Orn (Orinithine) AWMFAAVL → Val (Valine)