Development of new antimicrobial drugs and food preservatives that kill and/or prevent growth of pathogenic bacteria is thus of extreme importance. However, since the Golden area of antibiotics discovery (40 to 60s), where several new antibiotics where discovered, there has been a drastic decrease in the number of new antibiotics in the pharmacy pipeline.3
Gene-encoded ribosomally synthesized antimicrobial peptides (AMPs) are widely distributed in nature, being produced by bacteria, plants and animals, including humans. These peptides may be developed into useful antimicrobial additives and drugs. Bacteria-produced AMPs, generally referred to as (peptide-) bacteriocins, are very potent, being active at pico- to nano-molar concentrations. Bacteriocins produced by lactic acid bacteria (LAB) are of especial interest, as they are very potent and generally non-toxic to humans. Two bacteriocins produced by LAB, nisin and pediocin PA-1, have been approved as food additives.4-5
The LAB bacteriocins are generally cationic, 20–60 amino acid residues long, and kill bacteria by permeabilizing the cell membrane. 4-5 Most LAB bacteriocins target sensitive cells very specifically. Subtle structural differences in LAB bacteriocins lead to marked differences in their specificity and potency, and subtle differences in target-cells lead to marked differences in their susceptibility to these peptides. Recent results indicate that many of the bacteriocins6-7 , if not all LAB bacteriocins, exert their antimicrobial activity by a receptor-mediated mode-of-action. In contrast, less potent eukaryotic AMPs appear in many cases to bind in a non-chiral manner to bacterial membrane lipids and at sufficiently high peptide concentrations disrupt the membrane. The receptor mediated mode-of-action apparently involves so-called “membrane catalysis” 8-9, and is depicted in Figure 1.
Figure 1. Cartoon illustrating the receptor mediated mode of action. The bacteriocin is drawn in green, the membrane receptor is drawn in cyan and the immunity protein is drawn in yellow. The bacteriocin is unstructured in water, but is drawn to and interacts through ionic and hydrophobic interactions with the membrane lipids and becomes structured B). Upon interaction with the membrane the bacteriocin becomes orientation so that it may interact with the receptor C), and thereby enable it to bind to its receptor D). This binding then alters the three-dimensional (3D) structure of the receptor in a manner that leads to membrane leakage. E) Once the bacteriocin is bound to the receptor of the bacteriocin producing cell, the immunity protein bind to the receptor bacteriocin complex and blocks the efflux of ions.
For bacteriocins, the structure of the bacteriocins ad their receptors, the mechanisms governing target recognition, and the subsequent steps leading to membrane leakage and death of the target cells remain largely unknown. We study activity of bacteriocins, structures, the structure function relationship and bacteriocin receptors using methods such as: Protein production, Activity essays, Mutagenesis, Full genome sequencing, NMR spectroscopy, CD spectroscopy and Mass spectrometry.
Knowledge gained may allow development of bacteriocins into treatments of infections and additives for food preservation. We have several projects available to master degree students:
-Structure determination of 4 peptides that constitute the bacteriocin Aureocin A70
-Determination of the positioning of bacteriocins Ent-K1 in membrane bilayers
-Determination of the receptors of plantaricin S.
The work is done under the supervision of Per Eugen Kristiansen and in collaboration with Dzung Bao Diep (UMB).
References:
1. WHO, Antibiotic resistance. http://www.who.int/mediacentre/factsheets/antibiotic-resistance/en/ 2016.
2. WHO, Who is first global report on antibiotic resistance reveals serious, worldwide threat to public healt. http://www.who.int/mediacentre/news/releases/2014/amr-report/en/ 2014.
3. Lewis, K., Platforms for antibiotic discovery. Nat. Rev. Drug Discov. 2013, 12 (5), 371-387.
4. Nissen-Meyer, J.; Rogne, P.; Oppeg?rd, C.; Haugen, H. S.; Kristiansen, P. E., Structure-function relationships of the non-lanthionine-containing peptide (class II) bacteriocins produced by gram-positive bacteria. Curr. Pharm. Biotechnol. 2009, 10 (1), 19-37.
5. Oppeg?rd, C.; Rogne, P.; Emanuelsen, L.; Kristiansen, P. E.; Fimland, G.; Nissen-Meyer, J., The two-peptide class II bacteriocins: Structure, production, and mode of action. J. Mol. Microbiol. Biotechnol. 2007, 13 (4), 210-219.
6. Kjos, M.; Oppeg?rd, C.; Diep, D. B.; Nes, I. F.; Veening, J.-W.; Nissen-Meyer, J.; Kristensen, T., Sensitivity to the two-peptide bacteriocin lactococcin G is dependent on UppP, an enzyme involved in cell-wall synthesis. Mol. Microbiol. 2014, 92 (6), 1177-1187.
7. Diep, D. B.; Skaugen, M.; Salehian, Z.; Holo, H.; Nes, I. F., Common mechanisms of target cell recognition and immunity for class II bacteriocins. Proc. Natl. Acad. Sci. U. S. A. 2007, 104 (7), 2384-2389.
8. Castanho, M.; Fernandes, M. X., Lipid membrane-induced optimization for ligand-receptor docking: recent tools and insights for the "membrane catalysis" model.
Eur. Biophys. J. 2006, 35 (2), 92-103.
9. Sargent, D. F.; Schwyzer, R., Membrane lipid phase as catalyst for peptide receptor interactions. Proc. Natl. Acad. Sci. U. S. A. 1986, 83 (16), 5774-5778.