Thermodynamic stabilization of substrate protein within the GroEL:ES chaperonin cage.

GroEL/ES encapsulation of a destabilized Escherichia coli maltose-binding protein variant shifts its cooperative unfolding transition to a Tm of 52.4 °C, stabilizing it by 4.6 kcal mol−1.

• Why it matters: It remains unclear how confinement inside the ATP-regulated GroEL/ES nano-cage reshapes the folding energy landscape while preventing aggregation.
• What they did: The authors engineered quadruple mutant-MBP by four mutations to lower Tm from 63.6 °C to 44.3 °C, then measured folding and unfolding using hydrogen/deuterium exchange and single-molecule FRET with and without maltose.
• The result: GroEL/ES accelerated QM-MBP folding ~20-fold, produced a native-like structure in-cage, and made thermal unfolding reversible, implying the cavity environment is thermodynamically favorable for folding.

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