HdeB functions as an acid-protective chaperone in bacteria.
Enteric bacteria such as Escherichia coli utilize various acid response systems to counteract the acidic environment of the mammalian stomach. To protect their periplasmic proteome against rapid acid-mediated damage, bacteria contain the acid-activated periplasmic chaperones HdeA and HdeB. Activation of HdeA at pH 2 was shown to correlate with its acid-induced dissociation into partially unfolded monomers. In contrast, HdeB, which has high structural similarities to HdeA, shows negligible chaperone activity at pH 2 and only modest chaperone activity at pH 3. These results raised intriguing questions concerning the physiological role of HdeB in bacteria, its activation mechanism, and the structural requirements for its function as a molecular chaperone. In this study, we conducted structural and biochemical studies that revealed that HdeB indeed works as an effective molecular chaperone. However, in contrast to HdeA, whose chaperone function is optimal at pH 2, the chaperone function of HdeB is optimal at pH 4, at which HdeB is still fully dimeric and largely folded. NMR, analytical ultracentrifugation, and fluorescence studies suggest that the highly dynamic nature of HdeB at pH 4 alleviates the need for monomerization and partial unfolding. Once activated, HdeB binds various unfolding client proteins, prevents their aggregation, and supports their refolding upon subsequent neutralization. Overexpression of HdeA promotes bacterial survival at pH 2 and 3, whereas overexpression of HdeB positively affects bacterial growth at pH 4. These studies demonstrate how two structurally homologous proteins with seemingly identical in vivo functions have evolved to provide bacteria with the means for surviving a range of acidic protein-unfolding conditions.
From the Department of Molecular, Cellular, and Developmental Biology and.
Jan-Ulrik
JU
Dahl
From the Department of Molecular, Cellular, and Developmental Biology and the Howard Hughes Medical Institute, University of Michigan, Ann Arbor, Michigan 48109-1048.
Philipp
P
Koldewey
From the Department of Molecular, Cellular, and Developmental Biology and the Howard Hughes Medical Institute, University of Michigan, Ann Arbor, Michigan 48109-1048.
Loïc
L
Salmon
From the Department of Molecular, Cellular, and Developmental Biology and the Howard Hughes Medical Institute, University of Michigan, Ann Arbor, Michigan 48109-1048.
Scott
S
Horowitz
From the Department of Molecular, Cellular, and Developmental Biology and the Howard Hughes Medical Institute, University of Michigan, Ann Arbor, Michigan 48109-1048 jbardwel@umich.edu.
James C A
JC
Bardwell
From the Department of Molecular, Cellular, and Developmental Biology and the Howard Hughes Medical Institute, University of Michigan, Ann Arbor, Michigan 48109-1048 ujakob@umich.edu.
Ursula
U
Jakob
D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D006851:Hydrochloric Acid / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D050296:Microbial Viability / Q000187:drug effects; D018832:Molecular Chaperones / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019897:Periplasm / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D055503:Protein Multimerization; D058767:Protein Unfolding; D013312:Stress, Physiological
D029968:Escherichia coli Proteins; D018832:Molecular Chaperones; C084501:hdeA protein, E coli; C084502:hdeB protein, E coli; D006851:Hydrochloric Acid
Bacteria; Chaperone; Protein Aggregation; Protein Folding; Stress Response