The biology of lantibiotics from the lacticin 481 group is coming of age.

Lantibiotics are antimicrobial peptides from the bacteriocin family, secreted by Gram-positive bacteria. These peptides differ from other bacteriocins by the presence of (methyl)lanthionine residues, which result from enzymatic modification of precursor peptides encoded by structural genes. Several groups of lantibiotics have been distinguished, the largest of which is the lacticin 481 group. This group consists of at least 16 members, including lacticin 481, streptococcin A-FF22, mutacin II, nukacin ISK-1, and salivaricins. We present the first review devoted to this lantibiotic group, knowledge of which has increased significantly within the last few years. After updating the group composition and defining the common properties of these lantibiotics, we highlight the most recent developments. The latter concern: transcriptional regulation of the lantibiotic genes; understanding the biosynthetic machinery, in particular the ability to perform in vitro prepeptide maturation; characterization of a novel type of immunity protein; and broad application possibilities. This group differs in many aspects from the best known lantibiotic group (nisin group), but shares properties with less-studied groups such as the mersacidin, cytolysin and lactocin S groups.

Two acid-inducible promoters from Lactococcus lactis require the cis-acting ACiD-box and the transcription regulator RcfB.

We previously characterized three Lactococcus lactis promoters, P170, P1 and P3, which are induced by low pH. Here, we identified a novel 14 bp regulatory DNA region centred at around -41.5 and composed of three tetranucleotide sequences, boxes A, C and D. Boxes A and C contribute to P1 activity, whereas box D and the position of boxes ACD (renamed ACiD-box) are essential to P1 activity and acid response. We also identified a trans -acting protein, RcfB, which is involved in P170 and P1 basal activity and is essential for their pH induction. The regulator belongs to the Crp-Fnr family of transcription regulators. Overexpression of rcfB resulted in increased beta-galactosidase activities and lantibiotic lacticin 481 production from P170- and P1-controlled genes, respectively, in acid condition. RcfB is thus probably activated when cells encounter an acid environment. rcfB is co-transcribed with genes encoding an universal stress-like protein and a multidrug transporter. RcfB plays a role in acid adaptation, as the survival rate of an rcfB mutant after a lethal acid challenge was 130-fold lower than that of the wild-type strain, when the bacteria were first grown in acidic medium. The groESL promoter includes a sequence resembling an ACiD-box and the chaperone GroEL production is partly RcfB dependent in acid condition. Our results suggest that the ACiD-box could be the DNA target site of RcfB.

Maturation by LctT is required for biosynthesis of full-length lantibiotic lacticin 481.

In lantibiotic lacticin 481 biosynthesis, LctT cleaves the precursor peptide and exports mature lantibiotic. Matrix-assisted laser desorption ionization-time of flight mass spectrometry revealed that a truncated form of lacticin 481 is produced in the absence of LctT or after cleavage site inactivation. Production of truncated lacticin 481 is 4-fold less efficient, and its specific activity is about 10-fold lower.

Regulation of lantibiotic lacticin 481 production at the transcriptional level by acid pH.

The lantibiotic lacticin 481 operon (lctAMTFEG) is mainly transcribed from P1 and P3, two promoters lying upstream of lctA. A weak additional promoter allows independent expression of the immunity genes (lctFEG). Lacticin 481 production by Lactococcus lactis is stimulated by the acidification due to lactic acid production, and by artificially lowering the pH of the medium. This regulation occurs at the transcriptional level, since P1 and P3 are both acid-induced. P1 is weaker but more tightly regulated than P3. As no specific regulator is encoded by the lacticin 481 operon, P1 and P3 are likely controlled by a general regulator.

Bacteriocin detection from whole bacteria by matrix-assisted laser desorption ionization-time of flight mass spectrometry.

Class I bacteriocins (lantibiotics) and class II bacteriocins are antimicrobial peptides secreted by gram-positive bacteria. Using two lantibiotics, lacticin 481 and nisin, and the class II bacteriocin coagulin, we showed that bacteriocins can be detected without any purification from whole producer bacteria grown on plates by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS). When we compared the results of MALDI-TOF-MS performed with samples of whole cells and with samples of crude supernatants of liquid cultures, the former samples led to more efficient bacteriocin detection and required less handling. Nisin and lacticin 481 were both detected from a mixture of their producer strains, but such a mixture can yield additional signals. We used this method to determine the masses of two lacticin 481 variants, which confirmed at the peptide level the effect of mutations in the corresponding structural gene.

Human galectin-8 isoforms and cancer.

Galectins are animal lectins that can specifically bind beta-galactosides. Thirteen galectins have already been described. This review focuses on a specific member of this family: galectin-8. This galectin was discovered in prostate cancer cells eight years ago and has been studied extensively in the last few years. The galectin-8 gene ( LGALS8) encodes numerous mRNAs by alternate splicing and the presence of three unusual polyadenylation signals. These mRNAs encode six different isoforms of galectin-8: three belong to the tandem-repeat galectin group (with two CRDs linked by a hinge peptide) and three to the prototype group (with one CRD). Various studies showed that galectin-8 is widely expressed in tumor tissues as well as in normal tissues. The level of galectin-8 expression may correlate with the malignancy of human colon cancers and the degree of differentiation of lung squamous cell carcinomas and neuro-endocrine tumors. Recently, the differences in galectin-8 expression levels between normal and tumor tissues have been used as a guide for the selection of strategies for the prevention and treatment of lung squamous cell carcinoma. These experiments are still under investigation, but demonstrate the potential of galectin-8 research to enhance our understanding of, and possibly prevent, the process of neoplastic transformation.