摘要

       世界范围内多重耐药鲍曼不动杆菌（MDRAb）感染的发病率不断上升，这就要求开发新型抗生素。人防御素5（Human defensin 5，HD5）是一种具有复杂结构和抗菌活性的内源性多肽，本研究试图通过去除二硫键来简化HD5的结构。我们发现Cys2-4键是HD5灭活MDRAb所必需的，但其抗菌活性明显减弱。然后，我们将非阳离子和非疏水残基替换为电正性Arg，以提高含有Cys2-4键的HD5衍生物的抗菌活性，得到另一种衍生物HD5d5。体外抗菌实验和放射性伤口感染动物实验均表明，HD5d5在消除MDRAb方面比HD5有效得多。进一步研究发现，HD5d5能有效地结合外膜脂质A并穿透膜，导致细菌溃灭和肽移位。与HD5相比，HD5d5在MDRAb的细胞质中定位的分子更多，HD5d5降低超氧化物歧化酶和过氧化氢酶活性的效率更高，导致有害微生物活性氧的积累。此外，在50μg/ml浓度下，HD5不能抑制鲍曼不动杆菌（AbOmpA）的致病性外膜蛋白A，而HD5d5与AbOmpA结合强烈，具有显著的毒素中和能力，从而扩大了可用于治疗MDRAb感染的药物种类。

        The increasing incidence of multidrug-resistant Acinetobacter baumannii (MDRAb) infections worldwide has necessitated the development of novel antibiotics. Human defensin 5 (HD5) is an endogenous peptide with a complex architecture and antibacterial activity against MDRAb In the present study, we attempted to simplify the structure of HD5 by removing disulfide bonds. We found that the Cys2-4 bond was most indispensable for HD5 to inactivate MDRAb, although the antibacterial activity of the derivative was significantly attenuated. We then replaced the noncationic and nonhydrophobic residues with electropositive Arg to increase the antibacterial activity of HD5 derivative that contains a Cys2-4 bond, obtaining another derivative termed HD5d5. The in vitro antibacterial assay and irradiation-wound-infection animal experiment both showed that HD5d5 was much more effective than HD5 at eliminating MDRAb Further investigations revealed that HD5d5 efficiently bound to outer membrane lipid A and penetrated membranes, leading to bacterial collapse and peptide translocation. Compared to HD5, more HD5d5 molecules were located in the cytoplasm of MDRAb, and HD5d5 was more efficient at reducing the activities of superoxide dismutase and catalase, causing the accumulation of reactive oxygen species that are detrimental to microbes. In addition, HD5 failed to suppress the pathogenic outer membrane protein A of Acinetobacter baumannii (AbOmpA) at concentrations up to 50 μg/ml, whereas HD5d5 strongly bound to AbOmpA and exhibited a dramatic toxin-neutralizing ability, thus expanding the repertoire of drugs that is available to treat MDRAb infections.

         https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5786806/