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.