Exploring the selectivity and engineering potential of an NRPS condensation domain involved in the biosynthesis of the thermophilic siderophore fuscachelin

Condensation (C) domains are the key component linking different monomers together, typically forming peptide bonds and occasionally ester bonds, during the nonribosomal peptide synthetase (NRPS). While A domains have been well characterised due to their role in selectivity of the monomers and functioning as a gate keeper in the NRPS biosynthesis, C domains have been a subject of debate as they have not demonstrated signs of “A-domain like” side chain selectivity of its acceptor side. Here, we report our biochemical and structural characterisation of the selectivity of the fuscachelin C3-domain showing that it is not broadly flexible for monomers at the acceptor site, suggesting the need to consider C-domain mutation regarding future NRPS engineering.