SALMONELLA-TYPHIMURIUM RESPONSES TO A BACTERICIDAL PROTEIN FROM HUMANNEUTROPHILS

Bactericidal/permeability-increasing protein [BPI] is a cationic antim icrobial protein from neutrophils that specifically binds to the surfa ces of Gram-negative bacteria via the lipid A component of lipopolysac charide. To obtain information about the responses of Salmonella typhi murium to cell-surface damage by BPI, two-dimensional gel electrophore sis and N-terminal microsequencing were used to identify proteins that were induced or repressed following BPI treatment. The majority of th e affected proteins are involved in central metabolic processes. Upon addition of BPI, the beta-subunit of the F-1 portion of Escherichia co il ATP synthase was repressed threefold whereas six proteins were indu ced up to 11-fold. Three of the latter were identified as lipoamide de hydrogenase, enoyl-acyl carrier protein reductase, and the heat-shock protein HtpG. Additionally, a novel protein, BipA, was identified that is induced over sevenfold by BPI; sequence analysis suggests that it belongs to the GTPase superfamily and interacts with ribosomes. A cons erved direct-repeat motif is present in the regulatory regions of seve ral BPI-inducible genes, including the bipA gene. Only one of the BPI- responsive proteins was induced when cells were treated with polymyxin B, which also binds to lipid A. We therefore conclude that BPI and po lymyxin B affect different global regulatory networks in S. typhimuriu m even though they bind with high affinity to the same cell-surface co mponent.