Enterocin

Stereodivergence in Nature encapsulates both enzymatic (biosynthetic) and non-enzymatic (chemical) diversification of natural product scaffolds arising from a single biosynthetic pathway. Herein, we report a fascinating example of stereodivergence for the bacterial polyketide enterocin, which we observed to undergo a series of facile skeletal rearrangements in solution, leading to four distinct isomeric structures. The final distribution of the four isomers was found to be highly sensitive to the conditions used, including solvent, temperature and pH. In this study, we have investigated the kinetics of these isomeric conversions, and using a combination of DFT and thermochemical calculations, were able to establish a mechanism detailing a concerted rearrangement and an unusual "gymnastic" sequence of pseudo-chair-boat conformational interconversions. In addition to these kinetic and mechanistic studies, we also performed a semisynthetic study aimed at stabilising the enterocin scaffold. In total, seven analogues of enterocin were synthesised and investigated for their stability and in vitro activity against a panel of bacteria, fungi, plants and mammalian cells.

Food preservation is a method used to handle and treat food products to slow down food spoilage and subsequently reduce the risk of foodborne illness. Nowadays, the demand for natural preservatives over chemical preservatives in food is increasing due to the awareness of consuming healthy food products without the risk of harmful side effects. Thus, the research and development of preservation techniques, referred to as biopreservation, is growing rapidly. In biopreservation methods, microorganisms that are known as lactic acid bacteria (LAB) and their antimicrobial substances are used to extend shelf life and maintain the nutritional value of foods. Among the most studied LAB are from the genusEnterococcus, which produces a bacteriocin called enterocin. Bacteriocins are ribosomal-synthesized antimicrobial peptides that are capable of inhibiting the growth of pathogenic bacteria that cause spoilage in food. LAB is generally regarded as safe (GRAS) for human consumption. The current application of LAB, notablyEnterococcussp. in the biopreservation of meat and meat-based products was highlighted in this review. This report also includes information on the effects of enzymes, temperature, and pH on the stability of bacteriocin produced byEnterococcussp. An extensive compilation of numerous industry procedures for preserving meat has also been emphasized, highlighting the benefits and drawbacks of each method.

The mechanism of action of the anti-Listeria peptide enterocin CRL35 was studied with biophysical tools by using lipid mixtures that mimicked Gram-positive plasma membranes. Langmuir monolayers and infrared spectroscopy indicated that the peptide readily interacted with phospholipid assembled in monolayers and bilayers to produce a dual effect, depending on the acyl chains. Indeed, short chain mixtures were disordered by enterocin CRL35, but the gel-phases of membranes composed by longer acyl chains were clearly stabilized by the bacteriocin. Structural and functional studies indicated that non-bilayer states were formed when liposomes were co-incubated with enterocin CRL35, whereas significant permeabilization could be detected when bilayer and non-bilayer states co-existed. Results can be explained by a two-step model in which the N-terminal of the peptide firstly docks enterocin CRL35 on the lipid surface by means of electrostatic interactions; then, C-terminal triggers membrane perturbation by insertion of hydrophobic α-helix.