Model of insertion and release of a large solute into and from a biopolymer complex

► Our results should have impact on the research of the chaperonin GroEL. ► We succeed in elucidating the insertion/release mechanisms consistently for the first time. ► With a simple model, the switch from insertion to release is beautifully reproduced. ► Solute solvation within a domain confined on the scale of a nanometer plays a key role.