Characterization of functional domains of lantibiotic-binding immunity protein, NukH, from Staphylococcus warneri ISK-1

The immunity to a lantibiotic, nukacin ISK-1, is conferred by NukFEG (ABC transporter) and NukH (lantibiotic-binding protein) cooperatively. The present study identifies the functional domains of NukH. The topological analysis indicated that NukH possesses two external loops and three transmembrane helices. Deletion of N or C terminus of NukH did not affect the function. Amino acids substitutions in the respective loops abolished the function. Deletion of the third transmembrane helix resulted in loss of immunity but did not affect the binding activity. These findings suggested that the whole structure of NukH, except for N and C termini, is essential for its full immunity function, and that NukH inactivates nukacin ISK-1 after binding.