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x-ray structure of bacteriocin as-48 at ph 4.5. sulphate bound form
Bacteriocin AS-48 is a cyclic peptide antibiotic produced by the eubacteria Enterococcus faecalis (Streptococcus faecalis) that shows a broad antimicrobial spectrum against both Gram-positive and Gram-negative bacteria. Bacteriocin AS-48 is encoded by the pheromone-responsive plasmid pMB2, and acts on the plasma membrane in which it opens pores leading to ion leakage and cell death. The globular structure of bacteriocin AS-48 is composed of five alpha helices enclosing a hydrophobic core. The mammalian NK-lysin effector protein of T and natural killer cells has a similar structure, though it lacks sequence homology with bacteriocins AS-48.
Bacteriocin uses components of the mannose phosphotransferase system (man-PTS) of susceptible cells as target/receptor. The immunity protein LciA forms a strong complex with the receptor proteins and the bacteriocin, thereby preventing cells from being killed. The complex between LciA and the man-PTS components (IIAB, IIC, and IID) appears to involve an on–off type mechanism that allows complex formation only in the presence of bacteriocin; otherwise no complexes were observed between LciA and the receptor proteins.
- González C, Langdon GM, Bruix M, Gálvez A, Valdivia E, Maqueda M, Rico M (October 2000). "Bacteriocin AS-48, a microbial cyclic polypeptide structurally and functionally related to mammalian NK-lysin". Proc. Natl. Acad. Sci. U.S.A. 97 (21): 11221–6. doi:10.1073/pnas.210301097. PMC . PMID 11005847.
- Kjos M, Nes IF, Diep DB (2011). "Mechanisms of resistance to bacteriocins targeting the mannose phosphotransferase system.". Appl Environ Microbiol. 77 (10): 3335–42. doi:10.1128/AEM.02602-10. PMC . PMID 21421780.