Divergent Genetic Control of Protein Solubility and Conformational Quality in Escherichia coli

• Published in: Journal of molecular biology 2007-11, Vol.374 (1), p.195-205
• Main Authors: García-Fruitós, Elena, Martínez-Alonso, Mónica, Gonzàlez-Montalbán, Nuria, Valli, Minoska, Mattanovich, Diethard, Villaverde, Antonio
• Format: Article
• Language: English
• Subjects: Cytosol - metabolism; DnaK; E. coli; Escherichia coli; Escherichia coli - genetics; Escherichia coli - growth & development; Escherichia coli - metabolism; Escherichia coli Proteins - chemistry; Escherichia coli Proteins - genetics; Heat-Shock Response; HSP70 Heat-Shock Proteins - genetics; HSP70 Heat-Shock Proteins - metabolism; Inclusion Bodies; Molecular Chaperones - genetics; Molecular Chaperones - metabolism; Mutation; Protein Denaturation; Protein Folding; protein solubility; Protein Structure, Secondary; quality control; Solubility
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/j.jmb.2007.09.004

In bacteria, protein overproduction results in the formation of inclusion bodies, sized protein aggregates showing amyloid-like properties such as seeding-driven formation, amyloid-tropic dye binding, intermolecular β-sheet architecture and cytotoxicity on mammalian cells. During protein deposition, exposed hydrophobic patches force intermolecular clustering and aggregation but these aggregation determinants coexist with properly folded stretches, exhibiting native-like secondary structure. Several reports indicate that inclusion bodies formed by different enzymes or fluorescent proteins show detectable biological activity. By using an engineered green fluorescent protein as reporter we have examined how the cell quality control distributes such active but misfolded protein species between the soluble and insoluble cell fractions and how aggregation determinants act in cells deficient in quality control functions. Most of the tested genetic deficiencies in different cytosolic chaperones and proteases (affecting DnaK, GroEL, GroES, ClpB, ClpP and Lon at different extents) resulted in much less soluble but unexpectedly more fluorescent polypeptides. The enrichment of aggregates with fluorescent species results from a dramatic inhibition of ClpP and Lon-mediated, DnaK-surveyed green fluorescent protein degradation, and it does not perturb the amyloid-like architecture of inclusion bodies. Therefore, the Escherichia coli quality control system promotes protein solubility instead of conformational quality through an overcommitted proteolysis of aggregation-prone polypeptides, irrespective of their global conformational status and biological properties.