Solubilization of Protein Aggregates by the Acid Stress Chaperones HdeA and HdeB

Abderrahim Malki,Hai-Tuong Le,Sigrid Milles,Renée Kern,Teresa Caldas,Jad Abdallah,Gilbert Richarme

doi:10.1074/jbc.m800869200

Abderrahim Malki, Hai-Tuong Le + Show 5 more

Open Access

https://doi.org/10.1074/jbc.m800869200

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Abstract

The acid stress chaperones HdeA and HdeB of Escherichia coli prevent the aggregation of periplasmic proteins at acidic pH. We show in this report that they also form mixed aggregates with proteins that have failed to be solubilized at acidic pH and allow their subsequent solubilization at neutral pH. HdeA, HdeB, and HdeA and HdeB together display an increasing efficiency for the solubilization of protein aggregates at pH 3. They are less efficient for the solubilization of aggregates at pH 2, whereas HdeB is the most efficient. Increasing amounts of periplasmic proteins draw increasing amounts of chaperone into pellets, suggesting that chaperones co-aggregate with their substrate proteins. We observed a decrease in the size of protein aggregates in the presence of HdeA and HdeB, from very high molecular mass aggregates to 100-5000-kDa species. Moreover, a marked decrease in the exposed hydrophobicity of aggregated proteins in the presence of HdeA and HdeB was revealed by 1,1'-bis(4-anilino)naphtalene-5,5'-disulfonic acid binding experiments. In vivo, during the recovery at neutral pH of acid stressed bacterial cells, HdeA and HdeB allow the solubilization and renaturation of protein aggregates, including those formed by the maltose receptor MalE, the oligopeptide receptor OppA, and the histidine receptor HisJ. Thus, HdeA and HdeB not only help to maintain proteins in a soluble state during acid treatment, as previously reported, but also assist, both in vitro and in vivo, in the solubilization at neutral pH of mixed protein-chaperone aggregates formed at acidic pH, by decreasing the size of protein aggregates and the exposed hydrophobicity of aggregated proteins.

Highlights

In their natural habitats, bacteria are constantly under assault from a vast array of environmental stresses, including UV irradiation, heat, oxidative, osmotic, and pH stresses [1]
Further protection against acid stress is obtained by decreasing the permeability of the inner and outer membranes to protons and by reversing the cytoplasmic membrane potential to an inside-positive potential that slows the proton influx into the cell [2, 7, 8]
Bacteria can reorientate their metabolism toward pathways that decrease proton production or increase amine production with a consequent alkalinization [6, 9] several protective proteins, such as the DnaK and GroEL chaperone machines [10] and several DNA repair enzymes [11], may be induced upon acid stress

Summary

Introduction

Bacteria are constantly under assault from a vast array of environmental stresses, including UV irradiation, heat, oxidative, osmotic, and pH stresses [1]. To test the solubilization of protein aggregates by acid stress chaperones, we incubated periplasmic extracts from the hdeA mutant at either pH 3 or 2 for 60 min at 25 °C, either alone or with purified HdeA, HdeB, or both together, followed by centrifugation for 10 min at 15,000 ϫ g.

Results

Conclusion