Opening image: The heptameric GroEL ring. Click here to view down the seven-fold axis of symmetry. The ring is shown in the closed conformation (no ADP).

Click here to change to side view. rotation.

During the '90s the bacterial GroE chaperone became the paradigm of a protein folding machine. This lesson explores the architecture of the GroEL and GroES subunits and their assembly into heptameric rings.

Each GroEL (L for large) ring contains seven identical 60 kD subunits, hence the designation chaperonin-60. The seven cpn60 subunits are packed side-by-side, forming a ring that surrounds a central water-filled cavity. The ring is 140Å in diameter. The entrance to the central cavity is 30Å wide. The vertical walls of the entrance are nonpolar and bind amphiphilic helices of partially unfolded or misfolded proteins. the non-polar residues lining the entrance to the central channel.

We will explore the individual cpn60 subunits in Part 2.

GroES (S for small) contains seven identical 10 kD subunits, hence the designation chaperonin-10.

One cpn10 subunit of the GroES ring is shown above. The bottom surface of the red loop, dubbed the "foot", is nonpolar. spacefilled model.

nonpolar residues in the foot.

the assembly of the GroES lid. Note that the GroES heptameric ring, which is hollow, resembles an upside down saucer.

The catalytic cycle includes an allosteric transition that occurs upon cooperative binding of seven ATP molecules to the GroEL subunits. This conformational change allows the GroES lid to attach to the apical rim of the GroEL cylinder to form a bullet-shaped complex known as Anfinsen's cage (see Part 3). But first let's look at how GroEL changes its conformation during the catalytic cycle.