Acinetobacter baumannii is a ubiquitous bacteria that is increasingly becoming a formidable nosocomial pathogen. Due to its clinical relevance, studies on the bacteria’s secretory molecules especially extracellular proteases are of interest primarily in relation to the enzyme’s role in virulence. Besides, favorable properties that extracellular proteases possess may be exploited for commercial use thus there is a need to investigate extracellular proteases from Acinetobacter baumannii to gain insights into their catalytic properties. In this study, an extracellular subtilisin-like serine protease from Acinetobacter baumannii designated as SPSFQ that was isolated from fermented food was recombinantly expressed and characterized. The mature catalytically active form of SPSFQ shared a high percentage sequence identity of 99% to extracellular proteases from clinical isolates of Acinetobacter baumannii and Klebsiella pneumoniae as well as a moderately high percentage identity to other bacterial proteases with known keratinolytic and collagenolytic activity. The homology model of mature SPSFQ revealed its structure is composed of 10 β-strands, 8 α-helices, and connecting loops resembling a typical architecture of subtilisin-like α/β motif. SPSFQ is catalytically active at an optimum temperature of 40 °C and pH 9. Its activity is stimulated in the presence of Ca²⁺ and severely inhibited in the presence of PMSF. SPSFQ also displayed the ability to degrade several tissue-associated protein substrates such as keratin, collagen, and fibrin. Accordingly, our study shed light on the catalytic properties of a previously uncharacterized extracellular serine protease from Acinetobacter baumannii that warrants further investigations into its potential role as a virulence factor in pathogenicity and commercial applications.

鲍曼不动杆菌是一种普遍存在的细菌，正日益成为一种强大的医院病原体。由于其临床相关性，对细菌分泌分子特别是细胞外蛋白酶的研究主要与酶在毒力中的作用有关。此外，细胞外蛋白酶具有的有利特性可用于商业用途，因此需要研究来自鲍曼不动杆菌的细胞外蛋白酶，以深入了解它们的催化特性。在这项研究中，来自鲍曼不动杆菌的细胞外枯草杆菌蛋白酶样丝氨酸蛋白酶从发酵食品中分离出的指定为 SPFQ 的基因被重组表达和表征。成熟的催化活性形式的 SPSFQ 与来自鲍曼不动杆菌和肺炎克雷伯菌的临床分离株的细胞外蛋白酶具有 99% 的高百分比序列同一性，并且与具有已知角质溶解和胶原分解活性的其他细菌蛋白酶具有中等高百分比的同一性。成熟 SPFQ 的同源模型显示其结构由 10 个 β-链、8 个 α-螺旋和类似于枯草杆菌蛋白酶样 α/β 基序的典型结构的连接环组成。SPSFQ 在 40 °C 和 pH 9 的最佳温度下具有催化活性。它的活性在 Ca ^{2+存在下受到刺激}在 PMSF 存在下受到严重抑制。SPSFQ 还显示出降解几种组织相关蛋白底物（如角蛋白、胶原蛋白和纤维蛋白）的能力。因此，我们的研究揭示了来自鲍曼不动杆菌的先前未表征的细胞外丝氨酸蛋白酶的催化特性，这值得进一步研究其作为致病性和商业应用中的毒力因子的潜在作用。