Lantibiotics are antibacterial peptides containing unique thioether cross-links termed lanthionine and methyllanthionine. NukM, the modifying enzyme of nukacin ISK-1, which is produced by Staphylococcus warneri ISK-1, catalyzes the dehydration of specific Ser/Thr residues in a precursor peptide, followed by conjugative addition of intramolecular Cys to dehydrated residues to generate a cyclic structure. By contrast, the precursor peptide of nisin is modified by 2 enzymes, NisB and NisC, which mediate dehydration and cyclization, respectively. While the C-terminal domain of NukM is homologous to NisC, the N-terminal domain has no homology with other known proteins. We expressed and characterized the N- and C-terminal domains of NukM, NukM(N), and NukM(C) separately. In vitro reconstitution revealed that full-length NukM fully modified the substrate peptide NukA. NukM(N) partially phosphorylated, dehydrated, and cyclized NukA. By contrast, NukM(C) did not catalyze dehydration, phosphorylation, or cyclization reactions. Interaction studies using surface plasmon resonance analysis indicated that NukM and NukM(N) can bind NukA with high affinity, whereas NukM(C) has low substrate-recognition activity. These results suggest that NukM(N) is mainly responsible for substrate recognition and dehydration and that the whole NukM structure, including the C-terminal domain, is required for the complete modification of NukA. To the best of our knowledge, this is the first report providing insights into the in vitro catalytic activity of individual domains of a LanM-type modification enzyme. (c) 2015, The Society for Biotechnology, Japan. All rights reserved.