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Scientists have studied molecular interactions in the chaperonin protein GroEL. GroEL is alternately bound and unbound by a co-chaperonin, GroES. Against expectations, the ‘football’ complex — where two GroES units cap the cylindrical GroEL at either end — was roughly as prevalent as the single-bound ‘bullet’ complex. This implies that negative allosteric interactions preventing double-binding of GroEL sometimes fail, and the double-bound complex plays an active role in protein folding.