Table 1.
Characteristics of the nisin immunity protein NisI and nisin resistance protein NSR (* IC50 compared against sensitive Lactococcus lactis strain NZ9000; Sun et al., 2009; AlKhatib et al., 2014a; Hacker et al., 2015; Khosa et al., 2016).
| NisI | SaNSR | |
|---|---|---|
| Sequence length | 245 | 320 |
| Molecular weight (kDa) | 27.8 (full-length)/25.8 (processed) | 36.2 |
| Localization | Membrane attached/lipid-free | Membrane spanning |
| Sequence motif | N-terminal signal peptide | N-terminal transmembrane helix/conserved TASSAEM region |
| Function | Nisin binding | Nisin cleavage |
| Observed mechanism | Reversible cell clustering | Nisin proteolysis |
| Substrate specificity | N-terminus of nisin: rings A and B | C-terminus of nisin: rings D and E + last six amino acids |
| Conferred Immunity/resistance * | 8–10-fold | 18–20-fold |
| Important residues | Tyr152, Asp155 | His98, Ser236 |
| Binding affinity | 1 μM | Not determined |
| Structure determined | NMR | X-ray crystallography |
| Structure | Mainly β-sheet: two domains and a flexible linker | Helical bundle, protease fold, protease core domain |
| Binding site determined | NMR/mutational studies | Molecular dynamic simulations/mutational studies |