Previously Os, a 22 amino acid sequence of a defensin from the soft tick Ornithodoros savignyi, was found to kill Gram‐positive and Gram‐negative bacteria at low micromolar concentrations. In this study, we evaluated synthetic peptide analogues of Os for antibacterial activity with an aim to identify minimalized active peptide sequences and in so doing obtain a better understanding of the structural requirements for activity. Out of eight partially overlapping sequences of 10 to 12 residues, only Os(3–12) and Os(11–22) exhibit activity when screened against Gram‐positive and Gram‐negative bacteria. Carboxyamidation of both peptides increased membrane‐mediated activity, although carboxyamidation of Os(11–22) negatively impacted on activity against Staphylococcus aureus. The amidated peptides, Os(3–12)NH₂ and Os(11–22)NH₂, have minimum bactericidal concentrations of 3.3 μM against Escherichia coli. Killing was reached within 10 minutes for Os(3–12)NH₂ and only during the second hour for Os(11–22)NH₂. In an E. coli membrane liposome system, both Os and Os(3–12)NH₂ were identified as membrane disrupting while Os(11–22)NH₂ was less active, indicating that in addition to membrane permeabilization, other targets may be involved in bacterial killing. In contrast to Os, the membrane disruptive effect of Os(3–12)NH₂ did not diminish in the presence of salt. Neither Os nor its amidated derivatives caused human erythrocyte haemolysis. The contrasting killing kinetics and effects of amidation together with structural and liposome leakage data suggest that the 3–12 fragment relies on a membrane disruptive mechanism while the 11–22 fragment involves additional target mechanisms. The salt‐resistant potency of Os(3–12)NH₂ identifies it as a promising candidate for further development.

中文翻译：

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来自壁虱的OsDef2防御素的短酰胺化肽片段的抗菌功能。

以前，Os是来自软壁虱Ornithodoros savignyi的防御素的22个氨基酸序列，被发现可以杀死低微摩尔浓度的革兰氏阳性和革兰氏阴性细菌。在这项研究中，我们评估了Os的合成肽类似物的抗菌活性，目的是鉴定最小化的活性肽序列，从而更好地了解活性的结构要求。在针对10到12个残基的8个部分重叠的序列中，只有Os（3-12）和Os（11-22）在针对革兰氏阳性和革兰氏阴性细菌进行筛选时表现出活性。尽管Os（11-22）的羧酰胺化对金黄色葡萄球菌的活性有负面影响，但两种肽的羧酰胺化作用都增加了膜介导的活性。。酰胺化的肽Os（3–12）NH ₂和Os（11–22）NH ₂对大肠杆菌的最小杀菌浓度为3.3μM 。Os（3–12）NH ₂在10分钟内达到杀灭作用，Os（11–22）NH ₂仅在第二小时达到杀灭作用。在大肠杆菌膜脂质体系统中，Os和Os（3–12）NH ₂都被认为是膜破坏，而Os（11–22）NH ₂活性较低，这表明除了膜透化以外，其他目标可能是参与细菌杀灭。与Os相反，Os（3–12）NH ₂的膜破坏作用在盐的存在下并没有减少。Os或其酰胺化衍生物均未引起人红细胞溶血。相比之下，酰胺化的杀伤动力学和作用以及结构和脂质体渗漏数据表明3–12片段依赖于膜破坏机制，而11–22片段则涉及其他靶机制。Os（3-12）NH ₂的耐盐性使其成为进一步开发的有希望的候选者。