An Extracellular Loop of the Mannose Phosphotransferase System Component IIC Is Responsible for Specific Targeting by Class IIa Bacteriocins

Relative bacteriocin sensitivities of L. lactis B488 clones expressing different combinations of man-PTS genes of the listerial system (mpt) and the lactococcal system (ptn). (A) Wild-type IIC and IID genes (H1 and H2) and intergenic hybrids (H3 and H4); (B) intragenic IIC hybrids (H5 to H8); (C) six different clones with point mutations in mptC (G86S, G87N, Q88F, G89H, G89A, and G92A); (D) two clones with an exchange of one of the extracellular loops (H2X1 with 11 aa exchanged and H2X3 with 40 aa exchanged). Ptn proteins (PtnC and PtnD) are represented by black boxes and Mpt proteins (MptC and MptD) by white boxes. The different constructs were coexpressed with mptA (encoding a IIAB subunit in Listeria monocytogenes) to form a complete man-PTS complex (Table 3). Ten different class IIa bacteriocins were tested: pediocin PA-1 (Ped PA-1 [20, 29]), sakacin P (SakP [38]), leucocin C (LeuC [15]), avicin A (AviA [3]), leucocin A (LeuA [18]), enterocin P (EntP [4]), curvacin A (CurA [37]), bacteriocin RC714 (Bac RC714 [7]), hiracin JM79 (Hir JM79 [35]), and penocin A (PenA [9]). One arbitrary unit (AU) was defined as representing the MIC of clone H1, and the MICs of the other test clones were determined relative to this value. MIC values were determined at least three times. Clones were defined as not inhibited (NI) when the MIC values increased more than 600-fold (>600 AU). Growth inhibition by 2-deoxy-d-glucose (2-DG) is indicated with a plus sign; absence of inhibition is indicated with a minus sign.