LC-MS/MS analysis of the protein profiles of escherichia coli in response to the challenge of antibacterial peptides
Date of Issue2012
School of Chemical and Biomedical Engineering
Novel antibacterial drugs are in urgent need to overcome the continuous growth in the emergence of bacterial resistance to current antibiotics. Antibacterial peptides (ABPs), especially non-membrane-permeabilizing ABPs which kill bacteria by specific mechanisms other than direct membrane disruption, are excellent candidates for development as novel antibacterial drugs. Systematic and comprehensive understanding their mechanisms of action was thus urgently required. In this study, liquid chromatography-tandem mass spectrometry (LC-MS/MS) technique was utilized to analyze the protein profiles of Escherichia coli (E. coli) in response to the challenge of two representatives of non-membrane-permeabilizing ABPs, apidaecin IB and human neutrophil peptides 1 (HNP-1). A number of proteins which take essential roles in cellular protein quality control were found to be significantly changed. Levels of 60 kDa charperonin (GroEL) and 10 kDa charperonin (GroES), which together form the only essential chaperon system in E. coli cytoplasm under all growth conditions, were decreased; in contrast, levels of ATP-dependent protease ClpX and FtsH, which located in cytoplasm and inner membrane respectively, were increased. The increase in the proteases was probably involved in a compensatory response to the suppression effect. However, the overproduction of FtsH further intensified the degrading of UDP-3-O-acyl-N-acetylglucosamine deacetylase (LpxC), an enzyme catalyzing the first committed step in the biosynthesis of the lipid A moiety of lipopolysaccharide (LPS). As the same reaction precursor (R-3-hydroxymyristoyl-ACP) is used by LpxC for the biosynthesis of the lipid A moiety of LPS and by (3R)-hydroxymyristoyl-[acyl-carrier-protein] dehydratase (FabZ) for the synthesis of fatty acid, the reduction in LpxC led to further unbalanced synthesis of LPS and phospholipids and the loss of membrane lipid homeostasis. However, in response to HNP-1 challenge, levels of a number of enzymes in glycolysis were decreased, including 6-phosphofructokinase isozyme 1, glyceraldehyde-3-phosphate dehydrogenase A, phosphoglycerate kinase, enolase, and pyruvate kinase; in contrast, levels of enzymes (dehydrogenase and aconitate hydratase 2) which regulate the conversion of pyruvate into isocitrate were increased. In concert with the decreasing in cellular ATP and the slowing down in the growth of E. coli culture, central metabolism was suggested to be involved in the E. coli response to HNP-1 challenge.