STRUCTURAL-CHANGES OF THE ESCHERICHIA-COLI GROEL-GROES CHAPERONINS UPON COMPLEX-FORMATION IN SOLUTION - A NEUTRON SMALL-ANGLE SCATTERING STUDY

We applied neutron scattering in conjunction with deuterium (D-) label ing in order to obtain information about the domain structure of GroEL and GroES isolated and in the complex. Each subunit of the heptameric GroES consists of two domains, a core domain (Met1 to Lys15 and Lys34 to Ala97) and an intervening loop region (Glu16 to Ala33). Neutron sc attering shows that both regions change their conformation upon GroEL/ GroES complex formation. The interdomain angle between the core region s of the heptameric GroES increases from 120 to 140 degrees, leading t o a less dome-hire shape of GroES, and the loop regions turn inwards b y 75 degrees. The 23 C-terminal amino acids of the 14 GroEL subunits ( Lys526 to Met548), which are unresolved in the crystal structure, are located either at the bottom of the cavity formed by the seven-membere d GroEL ring or at the inner mall of the cavity. Upon complex formatio n the apical domains of GroEL move outwards, which facilitates binding of GroES at a GroEL-GroES center-to-center distance of (87 +/- 8) Ang strom. These structural changes may be important for the dissociation of the unfolded protein bound to the central cavity upon GroES binding . The overall structure determined by neutron scattering in solution t allies with the crystallographic model published after completion of t his study. Differences in the conformation of GroES observed in the co mplex by the two methods support the view that the chaperonin complex is a flexible molecule which might switch in solution between differen t conformations. (C) 1998 Academic Press.