NisI confers immunity against nisin, with high substrate specificity to prevent a suicidal effect in nisin-producing Lactococcus lactis strains. However, the NisI maturation process as well as its influence on nisin resistance has not been characterized. Here, we report the roles of lipoprotein signal peptidase II (Lsp) and prolipoprotein diacylglyceryl transferase (Lgt) in NisI maturation and nisin resistance of L. lactis F44. We found that the resistance of nisin of an Lsp-deficient mutant remarkably decreased, while no significant differences in growth were observed. We demonstrated that Lsp could cleave signal peptide of NisI precursor in vitro. Moreover, diacylglyceryl modification of NisI catalyzed by Lgt played a decisive role in attachment of NisI on the cell envelope, while it exhibited no effects on cleavage of the signal peptides of NisI precursor. The dissociation constant (K_D) for the interaction between nisin and NisI exhibited a 2.8-fold increase compared with that between nisin and pre-NisI with signal peptide by surface plasmon resonance (SPR) analysis, providing evidence that Lsp-catalyzed signal peptide cleavage was critical for the immune activity of NisI. Our study revealed the process of NisI maturation in L. lactis and presented a potential strategy to enhance industrial nisin production.

中文翻译：

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乳酸乳球菌的NisI成熟度及其对Nisin抗性的影响。

NisI赋予针对乳链菌肽的免疫力，具有高的底物特异性，可防止产生乳链菌肽的乳酸乳球菌菌株中的自杀作用。但是，NisI的成熟过程及其对乳链菌肽抗性的影响尚未得到表征。在这里，我们报告脂蛋白信号肽酶II（Lsp）和脂蛋白二酰基甘油基转移酶（Lgt）在乳酸乳球菌F44的NisI成熟和乳链菌肽抗性中的作用。我们发现，Lsp缺陷型突变体的乳链菌肽的抗性显着降低，而在生长方面没有观察到显着差异。我们证明了Lsp可以在体外裂解NisI前体的信号肽。此外，Lgt催化的NisI的二酰基甘油基修饰对NisI在细胞膜上的附着起决定性作用，而对NisI前体的信号肽的裂解没有影响。通过表面等离子体共振（SPR）分析，乳链菌肽和NisI之间相互作用的解离常数（K _D）比乳链菌肽和前NisI的解离常数增加了2.8倍，提供了Lsp催化的信号肽裂解的证据。对NisI的免疫活性至关重要。我们的研究揭示了乳酸乳球菌NisI的成熟过程，并提出了提高工业乳酸链球菌素产量的潜在策略。