Proteomic analysis of small acid soluble proteins in the spore core of Bacillus subtilis ΔprpE and 168 strains with predictions of peptides liquid chromatography retention times as an additional tool in protein identification

In both strains of B. subtilis, peptides characteristic for SASPs were found, however their identification confidence varied. According to the MS identity parameter Xcorr and difference between predicted and experimental retention times (ΔtR) four groups could be distinguished: correctly and incorrectly identified, potential false positives and false negatives. The ΔprpE strain was characterized by much higher amount of SASPs peptides than standard 168 and their identification confidence was, mostly for alpha- and beta-type SASP, satisfactory.The QSRR-based model for predicting retention times of the peptides, was a useful additional to MS tool, enhancing protein identification. Higher content of SASPs in strain lacking PrpE phosphatase suggests that this enzyme may influence their occurrence in the spores, lowering levels of these proteins.Although bacterial endospores have been studied for over 130 years, there are still questions about basic mechanisms of their unique features, i.e. high resistance to environmental stress, such as high temperatures, chemicals or radiation, which enable them long term survival in unfavorable conditions [1]. Bacillus subtilis (B. subtilis) is a sporulating, model organism often used in the biochemical, genetic and molecular research, concerning Gram positive bacteria. Its sporulation process is very complicated and requires space and time gene expression regulation. About 25% of genes in chromosome of this bacterium are involved in spore formation. What is more, there are already 154 proteins identified, characteristic exclusively for spores, which do not occur in vegetative cells [2]. Small acid soluble spore proteins (SASPs) have been evidenced to be one of specific spore components, which may have an influence on their resistance to unfavorable conditions [3]. The SASPs belong to a group of at least sixteen proteins found in the core of spores produced by B. subtilis [4-6]. Genes coding for those proteins are expressed only duri