Annotation of partial list of proteins profiled from Salmonella typhimurium in MALDI-TOF mass spectrometry microbial identification

Matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) has been shown to be a reliable tool for rapid identification of microbes down to the species level. But, many of the mass peaks in mass spectra of microorganisms remain to be annotated. This work presents a partial list of annotated proteins from the MALDI-TOF mass spectrum of Salmonella typhimurium. Reference proteome database used for the annotation workflow comes from UniProt, and an in-house MATLAB mass spectrum annotation software was used in annotating the profiled mass peaks. Results indicated good annotation of mass peaks with small errors ranging from 2 to 10 Da. Such errors could be accounted by mass accuracy of the mass spectrometer used or protein post-translational modification such as methylation. Proteins annotated include: Fels-2 prophage protein, 50S ribosomal protein L31, Glutaredoxin, and Gifsy-2 prophage excisionase. Presence of prophage protein in the annotated peak list meant that prophage genes are likely expressed in S. typhimurium, which holds significant implications for our understanding of cellular physiology, as well as possible roles of prophage proteins in pathophysiology of the intracellular bacterium. Overall, efforts to annotate the MALDI-TOF mass spectrum of S. typhimurium offers a glimpse into its cellular physiology and gene expression profile, that could, in theory, be replicated to other microorganisms to yield new insights in microbial cell biology, as well as expand our understandings of proteins possibly involved in pathogenesis in microbial pathogens.

基质辅助激光解吸电离飞行时间质谱（Matrix-assisted laser desorption/ionization time of flight mass spectrometry, MALDI-TOF MS）已被证实是一种可实现微生物至物种水平快速鉴定的可靠工具。然而，微生物质谱图谱中的多数质谱峰仍有待注释。本研究列出了鼠伤寒沙门氏菌（Salmonella typhimurium）MALDI-TOF质谱中已注释蛋白质的部分清单。本研究的注释流程采用的参考蛋白质组数据库源自UniProt，并借助自研MATLAB质谱注释软件对所获取的质谱峰进行注释。结果表明，本次质谱峰注释效果优异，误差范围仅为2至10 Da，此类误差可归因于所用质谱仪的质量精度限制，或是蛋白质发生的翻译后修饰（如甲基化）。本次注释的蛋白质包括：Fels-2原噬菌体蛋白、50S核糖体蛋白L31、谷氧还蛋白以及Gifsy-2原噬菌体切除酶。注释峰清单中检出原噬菌体蛋白，提示鼠伤寒沙门氏菌极可能存在原噬菌体基因的表达，这对于我们理解该菌的细胞生理学，以及原噬菌体蛋白在这种胞内致病菌病理生理学中的潜在作用均具有重要意义。总体而言，针对鼠伤寒沙门氏菌MALDI-TOF质谱的注释工作，为解析其细胞生理学与基因表达谱提供了新的视角；理论上，该方法可推广至其他微生物，既能为微生物细胞生物学研究带来新见解，也有助于拓展我们对微生物致病菌中可能参与致病过程的蛋白质的认知。