HdeB Functions as an Acid-protective Chaperone in Bacteria

Abstract

Background: Periplasmic chaperones HdeA and HdeB are involved in the acid stress response in Escherichia coli. Results: HdeB requires its folded and dimeric state to protect E. coli from protein aggregation at pH 4. Conclusion: HdeA and HdeB use different mechanisms to prevent periplasmic protein aggregation, allowing them to function over a broad pH range. Significance: This study furthers the understanding of how enteric bacteria counteract acid stress.

Folding Optimization In Vivo Uncovers New Chaperones

“…We have recently shown that HdeB is active in both the prevention of aggregation and in facilitating the refolding of proteins at acidic pH [11] consistent with previous suggestions that HdeB functions as an acid activated chaperone [48]. We recently reported that HdeB functions at pH values higher than what is optimal for HdeA [11]; HdeB exhibits maximal in vitro chaperone activity at pH 4, whereas HdeA has optimal chaperone activity at pH 2. Our selections were done on ordinary, not deliberately acidic media, implying that HdeB also has chaperone activity at more neutral pH values.…”

“…Indeed, there is good evidence that DppA from Rhodobacter has chaperone-like activity [40], and HdeB from E. coli has recently been shown to function as a chaperone at the moderately acidic pH of 4 [11]. Moreover, there is preliminary evidence that OppA may have weak chaperone activity in vitro [12].…”

“…Each protein was bound to HisTrap resin and eluted over a gradient from 0%–100% Ni 2+ buffer B. Fractions containing desired protein were pooled for ion-exchange chromatography using HiTrap Q sepharose under the same conditions as described for OsmY, except in choice of buffers (Ivy Q buffer A is 20 mM Tris, pH 8.0; Ivy Q buffer B is 20 mM Tris-HCl, 1 M NaCl, pH 8.0; Ivy storage buffer is 50 mM NaPi, 100 mM NaCl, pH 8.0; DppA Q buffer A is 20 mM Tris-HCl, 20 mM NaCl, pH 8.0; DppA Q buffer B is 20 mM Tris-HCl, 1 M NaCl, pH 8.0; DppA storage buffer is the same as Ivy storage buffer; OppA Q and storage buffers are the same as for DppA). HdeB-His 6 was purified as described [11]. Following purification, proteins were flash frozen using liquid nitrogen and stored at −80°C until use except in the case of OsmY, which was stored at −20°C.…”

Stress-Activated Chaperones: A First Line of Defense

“…However, while HdeA is chaperone-active under severe acid stress (e.g., pH <3), HdeB exhibits its highest chaperone activity at pH 4 [73]. Moreover, unlike HdeA, HdeB remains dimeric and apparently folded in its chaperone-active state, suggesting two rather distinct activation mechanisms for HdeA and HdeB [73].…”

“…However, while HdeA is chaperone-active under severe acid stress (e.g., pH <3), HdeB exhibits its highest chaperone activity at pH 4 [73]. Moreover, unlike HdeA, HdeB remains dimeric and apparently folded in its chaperone-active state, suggesting two rather distinct activation mechanisms for HdeA and HdeB [73]. Recently conducted pH-dependent NMR studies suggest that changes in HdeB's intrinsic dynamic properties could contribute to its chaperone function at pH 4 [74].…”