Annealing function of GroEL: structural and bioinformatic analysis.

Area of Science:

• Molecular Biology
• Protein Folding
• Structural Biology

Background:

• The Escherichia coli chaperonin system, GroEL-GroES, is crucial for preventing protein aggregation and facilitating substrate protein (SP) folding.
• The iterative annealing mechanism involves allostery-driven GroEL transitions that alter the SP's microenvironment, constituting the chaperonin's annealing action.

Purpose of the Study:

• To elucidate the molecular basis for altered SP-GroEL interactions during GroEL conformational transitions.
• To analyze residue-specific changes in accessible surface area and tertiary contacts during T-->R-->R" transitions.
• To evaluate the conservation patterns of residues involved in key chaperonin functions.

Main Methods:

• Utilized crystal structures of GroEL (T state), GroEL-ATP (R state), and the GroEL-GroES-(ADP)7 (R" state) complex.
• Determined residue-specific changes in accessible surface area and tertiary contacts.
• Performed multiple sequence alignments and chemical sequence entropy calculations to assess residue conservation.

Main Results:

• Significant changes in accessible surface area were observed in apical domain residues, with smaller changes in the equatorial domain.
• The T-->R transition alters the SP microenvironment, indicating GroEL's intrinsic annealing capability.
• Identified conserved peptide binding sites in the apical domain and conserved correlated mutations controlling allostery; charged solvent-exposed residues (Lys 226, Glu 252, Asp 253) in the T state are highly conserved.

Conclusions:

• GroEL acts as an annealing machine even without GroES, driven by T-->R transitions that modify the SP microenvironment.
• Residue conservation analysis reveals that specific chemical identities, rather than exact residues, are critical for chaperonin functions.
• Mutating conserved charged residues (Lys 226, Glu 252, Asp 253) may impair the chaperonin's annealing function.