Institute of Biochemistry and Biophysics, Polish Academy of Sciences (IBB PAS), Pawińskiego 5a, 02-106 Warsaw, Poland.
Int J Mol Sci. 2020 Oct 23;21(21):7860. doi: 10.3390/ijms21217860.
Lactic acid bacteria produce diverse antimicrobial peptides called bacteriocins. Most bacteriocins target sensitive bacteria by binding to specific receptors. Although a plethora of bacteriocins have been identified, for only a few of them the receptors they recognize are known. Here, we identified permease IIC and surface protein IID, two membrane subunits of the mannose-specific quaternary phosphotransferase system (Man-PTS), as a receptor for BacSJ, a subclass IId bacteriocin produced by subsp. BGSJ2-8. BacSJ shares 45% identity with another Man-PTS binding bacteriocin, garvicin Q (GarQ). Similarly to GarQ, BacSJ has a relatively broad activity spectrum acting against several Gram-positive bacteria, such as and harboring fairly similar Man-PTSs, but not against . To identify specific Man-PTS amino acids responsible for the sensitivity to BacSJ, and thus likely involved in the interaction with this bacteriocin, we generated eight independent BacSJ resistant mutants harboring five distinct missense mutations in the or genes encoding the IIC and IID subunits. Concurrently with the resistance to BacSJ, the mutants efficiently utilized mannose as a carbon source, which indicated functionality of their mutated Man-PTS. The amino acid substitutions in the mutants localized to the intracellular region of the IIC permease or to the extracellular parts of IID. This localization coincides with regions targeted by GarQ and some other Man-PTS-binding garvicins, pointing to similarities between all these bacteriocins in the mechanism of their interaction with Man-PTS. During the attack by these bacteriocins, subunits IID and IIC are assumed to function sequentially as a docking and an entry module allowing the toxic peptide to bind the cell and then open the pore. However, since not all of the BacSJ-resistant mutants exhibited cross-resistance to GarQ, we propose that BacSJ interacts with Man-PTS in a manner slightly different from that of GarQ.
乳酸菌产生多种称为细菌素的抗菌肽。大多数细菌素通过与特定受体结合来靶向敏感细菌。尽管已经鉴定出了大量的细菌素，但只有少数几种细菌素识别它们的受体。在这里，我们鉴定了甘露糖特异性四元磷酸转移酶系统（Man-PTS）的两个膜亚基，渗透酶 IIC 和表面蛋白 IID，作为 BacSJ 的受体，BacSJ 是由 subsp. BGSJ2-8 产生的 IId 细菌素。BacSJ 与另一种 Man-PTS 结合细菌素 garvicin Q (GarQ) 具有 45%的同源性。与 GarQ 类似，BacSJ 具有相对较宽的活性谱，可作用于几种革兰氏阳性细菌，例如 和 ，它们具有相当相似的 Man-PTS，但对 没有作用。为了鉴定对 BacSJ 敏感的特定 Man-PTS 氨基酸，从而可能参与与这种细菌素的相互作用，我们生成了八个独立的 BacSJ 抗性 突变体，它们在编码 IIC 和 IID 亚基的 或 基因中具有五个不同的错义突变。与 BacSJ 抗性同时，突变体有效地将甘露糖用作碳源，这表明它们突变的 Man-PTS 具有功能性。突变体中的氨基酸取代定位于 IIC 渗透酶的细胞内区域或 IID 的细胞外部分。这种定位与 GarQ 和一些其他 Man-PTS 结合 garvicin 靶向的区域重合，表明所有这些细菌素在与 Man-PTS 相互作用的机制上存在相似性。在这些细菌素的攻击过程中，假定亚基 IID 和 IIC 依次作为对接和进入模块发挥作用，允许毒性肽结合细胞，然后打开孔。然而，由于并非所有 BacSJ 抗性突变体都对 GarQ 表现出交叉抗性，因此我们提出 BacSJ 与 Man-PTS 的相互作用方式与 GarQ 略有不同。
