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GroEL recognises sequential and non-sequential linear structural motifs compatible with extended beta-strands and
J Chatellier1, A M Buckle, A R Fersht
1Cambridge University Chemical Laboratory and Cambridge Centre for Protein Engineering and MRC Centre, Hills Road, Cambridge, CB2 2QH, UK.
Journal of Molecular Biology
|September 24, 1999
Summary
The chaperonin GroEL protein binds diverse substrates by recognizing specific structural features, not just sequence. This protein acts as a temporary binding site for cellular intermediates and can also unfold substrates.
Area of Science:
- Molecular Biology
- Protein Folding
- Biochemistry
Background:
- The chaperonin GroEL (Hsp60) facilitates protein folding by binding unfolded or misfolded polypeptides.
- The specific recognition mechanisms and structural features GroEL targets remain largely undefined.
- Previous models suggested GroEL binds linear sequences, like extended beta-strands.
Purpose of the Study:
- To investigate the structural and chemical features recognized by the chaperonin GroEL.
- To determine the range of substrate conformations and residue types GroEL can bind.
- To elucidate the binding mechanisms underlying GroEL's roles in protein folding and unfolding.
Main Methods:
- Affinity panning using immobilized GroEL minichaperones (residues 191-376).
- Utilized a bacteriophage library displaying the fungal cellulose-binding domain of cellobiohydrolase I.
- Analyzed binding characteristics of specific mutants and substrate conformations (beta-strand, alpha-helix).
Main Results:
- GroEL binds substrates with non-sequential residues forming a constrained linear motif, similar to its previously identified peptide tag binding.
- The binding site accommodates various side-chain types, including polar and positively charged residues, not exclusively hydrophobic ones.
- GroEL can bind substrates in extended (approx. 7 residues) or helical (approx. 18 residues) conformations, indicating versatility.
Conclusions:
- GroEL recognizes a broader range of substrate structures than previously thought, including extended beta-strands, alpha-helices, and folded states with exposed side-chains.
- These findings support GroEL's dual function as a 'parking spot' for aggregation-prone intermediates and an unfolding machine.
- The chaperonin's ability to bind diverse motifs contributes to its essential role in maintaining cellular proteostasis.