The disordered mobile loop of GroES folds into a defined beta-hairpin uponbinding GroEL

The GroES mobile loop is a stretch of similar to 16 amino acids that exhibi ts a high degree of flexible disorder in the free protein. This loop is res ponsible for the interaction between GroES and GroEL, and it undergoes a fo lding transition upon binding to GroEL. Results derived from a combination of transferred nuclear Overhauser effect NMR experiments and molecular dyna mics simulations indicate that the mobile loop adopts a beta -hairpin struc ture with a Type I, G1 Bulge turn. This structure is distinct from the conf ormation of the loop in the cocrystal of GroES with GroEL-ADP but identical to the conformation of the bacteriophage-panned "strongly binding peptide" in the co-crystal with GroEL. Analysis of sequence conservation suggests t hat sequences of the mobile loop and strongly binding peptide were selected for the ability to adopt this hairpin conformation.