Abstract
Ribosomal subunit proteins of eight genome-sequenced lactic acid bacteria (LAB) were characterized by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) to provide a guideline for selecting reliable biomarkers used for the rapid identification of LAB. Subunit proteins with molecular weight over ca. 20,000 were typically difficult to detect. This phenomenon appeared to be due to the mass discrimination effect in MALDI-MS. Conserved post-translational modifications excluding N-terminal methionine loss were investigated by comparing the mass differences from sequence masses calculated from the amino acid sequences of the proteins with the post-translational modifications. Various errors in the amino acid sequences of the subunit proteins registered in protein databases could be detected by comparing amino acid sequences, and corrected by inspecting gene sequences. By eliminating the subunit proteins with higher molecular weight and post-translational modifications as well as other difficult to detect subunit proteins, 27 subunit proteins were finally selected as the reliable biomarkers.
