The biosynthetic pathway of Nisin and its regulatory factors

The biosynthetic pathway and regulatory factors of Nisin are as follows:

I. Biosynthetic Pathway

1. Precursor Peptide Synthesis

Under the stimulation of specific environmental factors, when the concentration of signaling molecules reaches a certain threshold, nisin genes begin to transcribe. Amino acids composing nisin, with the participation of aminoacyl-tRNA synthetase, covalently form aminoacyl-tRNA with transfer RNA (tRNA). Aminoacyl-tRNA binds to specific sites on messenger RNA (mRNA) containing the genetic code for nisin synthesis. Ribosomes bind to the initiation sequence of the mRNA molecule and start synthesizing the nisin precursor peptide along the codon sequence.

2. Processing and Transport

The proteolytic region of ATP-binding cassette transporter (ABCT) binds to the leader sequence of the precursor peptide, triggering ATP hydrolysis. The transporter undergoes a conformational change, excising the leader sequence. With the assistance of auxiliary proteins, mature nisin is transported extracellularly. The leader sequence of the precursor peptide contains 18–27 amino acid residues and a conserved di-glycine residue, serving as a recognition signal for the transport system.

II. Regulatory Factors

1. Two-Component Signal Transduction System (NisRK)

Nisin biosynthesis is regulated by a cell density-dependent quorum sensing mechanism. As a signaling molecule (peptide pheromone), it triggers the expression of pathway genes through promoters PnisA and PnisF via the two-component system nisrk, leading to the production of mature nisin. When the extracellular Nisin concentration reaches a certain level, it binds to the histidine kinase nisK on the cell membrane, causing autophosphorylation of nisK. The phosphate group is then transferred to the response regulator protein NisR. Phosphorylated NisR binds to the promoter region of target genes, activating the transcription of nisin biosynthesis genes.

2. Promoters

PnisA and PnisF are Nisin-inducible promoters playing a key role in nisin biosynthesis. Additionally, constitutive promoters such as P1 and P2 in the nisin gene cluster also regulate nisin synthesis to some extent.

3. Environmental Factors

Environmental factors such as medium composition, pH, and temperature significantly impact nisin biosynthesis. For example, lower pH can induce increased nisin production because promoters like PnisA exhibit higher activity under acidic conditions. Meanwhile, appropriate carbon sources, nitrogen sources, and nutrient concentrations affect the expression of nisin synthesis-related genes and cellular metabolic states, thereby influencing nisin yield.