Several Membrane and Cytoplasmic Proteins May be Associated with Virulence Reduction of Brucella Melitensis Strain RM57

Background: Brucella melitensis RM57, a mutant of B. melitensis M1981, is an effective vaccine candidate due to the reduced virulence. This study was aimed to explore the molecular mechanism of virulence reduction in Brucella melitensis RM57.Methods: The differentially expressed genes (DEGs) between samples from M1981 and RM57 were determined based on gene expression profiles and were used for protein subcellular localization (SCL) analysis. Then based on the SCL results, proteinprotein interaction (PPI) network analysis was performed, followed by function enrichment analysis and gene-drug interaction prediction.Results: A total of 403 DEGs were identified between the RM57 and M1981 groups. Then, 58 proteins were predicted based on the NCBI protein database, including 3 membrane proteins (nuoK, exbD, and cydB), 31 cytoplasmic proteins, and 2 periplasmic proteins. A PPI network was constructed, which consisted of 27 nodes, such as rpoB, rpoA, rpsP, rpoC, RpsA and nuoK, and 146 interactions. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of the proteins in the PPI networks showed that they were mainly enriched pathways of ribosome, and RNA polymerase, and functions related to biosynthetic process and metabolic process. Mitoxantrone, adriamycin, and daunorubicin were predicted to be target drugs of RpsA.Conclusions: The membrane proteins of nuoK, exbD, and cydB, and cytoplasmic proteins, such as rpoB, rpoA and rpsP, may contribute to the virulence reduction of the RM57 strain. RpsA may induce an immune response against brucellosis infection through ribosome pathway. These proteins may be targets for novel vaccine development.