Peptide and amino acid metabolism is controlled by an OmpR‐family response regulator in Lactobacillus casei

Abstract

A Lactobacillus casei BL23 strain defective in an OmpR-family response regulator encoded by LCABL_18980 (PrcR, RR11), showed enhanced proteolytic activity caused by overexpression of the gene encoding the proteinase PrtP. Transcriptomic analysis revealed that, in addition to prtP expression, PrcR regulates genes encoding peptide and amino acid transporters, intracellular peptidases and amino acid biosynthetic pathways, among others. Binding of PrcR to twelve promoter regions of both upregulated and downregulated genes, including its own promoter, was demonstrated by electrophoretic mobility shift assays showing that PrcR can act as a transcriptional repressor or activator. Phosphorylation of PrcR increased its DNA binding activity and this effect was abolished after replacement of the phosphorylatable residue Asp-52 by alanine. Comparison of the transcript levels in cells grown in the presence or absence of tryptone in the growth medium revealed that PrcR activity responded to the presence of a complex amino acid source in the growth medium. We conclude that the PrcR plays a major role in the control of the peptide and amino acid metabolism in L. casei BL23. Orthologous prcR genes are present in most members of the Lactobacillaceae and Leuconostocaceae families. We hypothesize that they play a similar role in these bacterial groups.

Bioprospecting for Bioactive Peptide Production by Lactic Acid Bacteria Isolated from Fermented Dairy Food

“…Comparative genome analyses support that proteolytic enzymes are highly variable at inter and intra-species level, mainly for CEP-encoding genes, determining a huge variability in BPs release among different LAB strains. Therefore, the proteolytic activity of a given strain and the resulting BP profiles in food matrix finally depend on its CEP and peptidase patterns, on gene variations, and on the environmental conditions, which modulate proteolytic gene expression [228]. Several evidences support that the lactococci and lactobacilli proteolytic systems are comparable in their components and modes of action in terms of converting milk proteins (primarily caseins) into oligopeptides and free amino acids.…”

“…The DNA-binding proteins YebC and PrcR are responsible for extracellular peptide-dependent repression of the genes of the proteolytic system in L. delbrueckii subsp. lactis CRL 581 and L. casei BL23, respectively [228,277] (Figure 3B). Differently from L. helveticus and Lc.…”

“…lactis, both these regulators are unresponsive to BCAA. Interestingly, PrcR was found to negatively regulate the BcaR gene encoding for a protein orthologous to BCARR, suggesting that PrcR could be the master regulator of a regulatory network responsive to amino acid starvation more complex than that found in in L. helveticus [228]…”

YebC, a putative transcriptional factor involved in the regulation of the proteolytic system of Lactobacillus

“…However, the low response of prtP to the presence or absence of tryptone suggests an additional regulatory system acting on this gene 37 . PrcR response is independent of the peptide or BCAA content 37 . On the other hand, no information about proteinase gene expression in response to peptides or BCAA in L .…”

“…casei BL23 PrcR controls a regulon of genes involved in amino acid supply 37 . However, the low response of prtP to the presence or absence of tryptone suggests an additional regulatory system acting on this gene 37 . PrcR response is independent of the peptide or BCAA content 37 .…”