Catch and release Chaperones are essential for proper protein folding inside cells, but their interactions with client proteins are difficult to study because they are dynamic. Jiang et al. used nuclear magnetic resonance spectroscopy to look at how the chaperones Hsp70 and Hsp40 work together in the client binding and release cycle. Hsp40 alters the folding properties of the client protein, perhaps unfolding a non-native state, by binding dynamically through multiple binding sites. Hsp70 binding to Hsp40 displaces the unfolded client. The released protein may either fold to its native state, or be rebound for another chaperone cycle. Science , this issue p. 1313