The regulatory mechanism of Nisin's biosynthesis

Nisin, a bioactive peptide produced by Lactococcus lactis, has a complex biosynthetic regulatory mechanism involving multiple levels such as gene expression, quorum sensing, and post-translational modification, as detailed below:

Gene Cluster Regulation: The biosynthesis of nisin is regulated by a gene cluster consisting of a series of genes, typically including 11 genes such as nisABTCIPRKFEG. Among them, nisA encodes the nisin precursor peptide; nisB and nisC participate in post-translational modification reactions, responsible for dehydrating serine and threonine residues in the precursor peptide to form dehydroalanine and dehydrobutyrate, and cyclizing with cysteine to form thioether bridges; nisT is involved in the transmembrane transport of the precursor nisin; nisP is a protease that processes the precursor nisin by cleaving the leader peptide to release mature nisin; nisI and nisFEG participate in the self-protection and immunity of nisin, preventing it from harming the producing strain itself; nisR and nisK form a two-component regulatory system, responsible for sensing and transmitting signals to regulate the biosynthesis of nisin.

Quorum Sensing Regulation: The biosynthesis of nisin is regulated by a quorum sensing mechanism. NisK is a histidine kinase that acts as a sensor, capable of perceiving Nisin molecules in the extracellular environment. When its concentration reaches a certain threshold,nisK undergoes autophosphorylation and then transfers the phosphate group to the response regulator protein nisR. Phosphorylated nisR binds to the promoter regions of nisA and nisF, activating the transcription of these genes, thereby promoting the biosynthesis of nisin. This quorum sensing mechanism links nisin synthesis to cell density, ensuring that it is synthesized in large quantities only when the cell count reaches a certain level.

Post-Translational Modification Regulation: The nisin precursor undergoes complex post-translational modifications to become active mature nisin. The post-translational modification system composed of proteins such as nisB and NisC modifies the Nisin precursor, forming five thioether rings containing special amino acids. The formation of these thioether rings not only endows it with a unique structure and stability but also affects its antibacterial activity. In addition, studies have found that some new genes, such as feud, may regulate the nisin biosynthetic system, influencing the efficiency of post-translational modification and its yield.

Nutrient Regulation: Nutrients also have an important impact on the biosynthesis of Nisin. For example, cysteine (Cys) is an important precursor for its synthesis, and a reasonable supply of Cys can improve its synthesis efficiency. Studies have shown that appropriate addition of Cys during the fermentation of Lactococcus lactis can increase its titer. Furthermore, arginine (Arg) plays a significant role in the growth and metabolism of Lactococcus lactis; it participates in energy production through the arginine deiminase (ADI) pathway. When Arg is deficient, it affects cell growth and nisin synthesis. At this time, cells upregulate the expression of peptidase-related genes to decompose proteins and polypeptides to meet their own needs, which also reflects the complexity of nutrient regulation on its biosynthesis.