Co-chaperonins from diverse organisms exhibit mobile loops which fold into a 
beta hairpin conformation upon binding to the chaperonin. GroES, Gp31, and human 
Hsp10 mobile loops exhibit a preference for the beta hairpin conformation in the 
free co-chaperonins, and the conformational dynamics of the human Hsp10 mobile 
loop appear to be restricted by nascent hairpin formation. Backbone 
conformational entropy must weigh against binding of co-chaperonins to 
chaperonins, and thus the conformational preferences of the loops may strongly 
influence chaperonin-binding affinity. Indeed, subtle mutations in the loops 
change GroEL-binding affinity and cause defects in chaperonin function, and 
these defects can be suppressed by mutations in GroEL which compensate for the 
changes in affinity. The fact that high-affinity co-chaperonin binding impairs 
chaperonin function has implications for the mechanism of chaperonin-assisted 
protein folding.