Characterization of three small proteins in Brucella abortus linked to fucose utilization

Elucidating the function of proteins less 50 amino acids in length is no small task. Nevertheless, small proteins can play vital roles in the lifestyle of bacteria and even the virulence of pathogens; thus, the investigation of the small proteome is warranted. Recently our group identified VtlR as a transcriptional activator of four genes, one of which is the well-studied small regulatory RNA, AbcR2, while the other three genes encode hypothetical small proteins, two of which are highly conserved among the order Rhizobiales. This study provides evidence that all three genes encode authentic small proteins and all three are highly expressed under oxidative stress, low pH, and stationary phase growth conditions. Fractionation of the cells revealed that the proteins are localized to the membranes of B. abortus. We demonstrate that the small hypothetical proteins under the transcriptional control of VtlR are not linked to attenuation observed with the vtlR mutant. However, there is an association between VtlR and the VtlR regulon to a phenotype involving growth inhibition by the sugar L-fucose, identified through the use of Biolog Phenotypic MicroArray Technology. This led us to identify a putative L-fucose transport system in B. abortus through the use of RNAseq analysis. Altogether, our observations better characterize the known VtlR regulon, which includes the sRNA abcR2, and three small proteins bab1_0914, bab2_0512, and bab2_0574; and adds to the scientific community’s understanding of the utility of small proteins in bacteria.