Department of Bioscience, Faculty of Science, Universiti Teknologi Malaysia, Skudai, Malaysia.
Structural Biology & Biophysics Department, Malaysian Genome Institute, Kajang, Selangor, Malaysia.
Protein J. 2021 Jun;40(3):419-435. doi: 10.1007/s10930-021-09986-5. Epub 2021 Apr 18.
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 Ca 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，它正日益成为一种强大的医院病原体。由于其临床相关性，对细菌分泌分子的研究，特别是细胞外蛋白酶，主要与酶在毒力中的作用有关。此外，细胞外蛋白酶所具有的有利特性可能被用于商业用途，因此需要研究鲍曼不动杆菌的细胞外蛋白酶，以深入了解其催化特性。在这项研究中，从发酵食品中分离到的鲍曼不动杆菌的一种细胞外枯草杆菌样丝氨酸蛋白酶被命名为 SPSFQ，它被重组表达并进行了特征描述。SPSFQ 的成熟催化活性形式与来自临床分离的鲍曼不动杆菌和肺炎克雷伯菌的细胞外蛋白酶具有 99%的高序列同一性，与具有已知角蛋白水解和胶原蛋白水解活性的其他细菌蛋白酶也具有中等高度的同一性。成熟 SPSFQ 的同源模型显示其结构由 10 个 β-折叠、8 个 α-螺旋和连接环组成，类似于枯草杆菌样 α/β 结构域的典型结构。SPSFQ 在 40°C 的最佳温度和 pH 9 下具有催化活性。其活性在 Ca 的存在下被刺激，而在 PMSF 的存在下被严重抑制。SPSFQ 还显示出能够降解几种与组织相关的蛋白底物的能力，如角蛋白、胶原蛋白和纤维蛋白。因此，我们的研究揭示了一种以前未被描述的鲍曼不动杆菌细胞外丝氨酸蛋白酶的催化特性，这为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提供了依据。
