9.B.91 The Bacteriocin 41 Immunity Protein (Bac41IP Family)
The conjugative plasmid pYI14 (61 kbp) from Enterococcus faecalis YI714, confers a pheromone response on its host and encodes bacteriocin 41 (bac41). Bacteriocin 41 (Bac41) only showed activity against E.faecalis. The determinant was located in a 6.6-kbp region with six open reading frames (ORFs) designated ORF7 (bacL1) ORF8 (bacL2), ORF9, ORF10, ORF11 (bacA), and ORF12 (bacI). They are aligned in this order and oriented in the same direction. ORFs bacL1, bacL2, bacA, and bacI are essential for expression of the bacteriocin in E. faecalis
Extracellular complementation of bacteriocin expression was possible for bacL1 and -L2 and bacA mutants. bacL1 and -L2 and bacA encoded bacteriocin component L and activator component A, respectively. The products of these genes are secreted into the culture medium and extracellularly complement bacteriocin expression. bacI encoded immunity, providing the host with resistance to its own bacteriocin activity. The bacL1-encoded protein had significant homology with lytic enzymes that attack the gram-positive bacterial cell wall. Sequence data for the deduced bacL1-encoded protein suggested that it has a domain structure consisting of an N-terminal signal peptide, a second domain with the enzymatic activity, and a third domain with a three-repeat structure directing the proenzyme to its cell surface receptor.