GroES

Heat shock 10 kDa protein 1 (Hsp10), also known as chaperonin 10 (cpn10) or early-pregnancy factor (EPF), is a protein that in humans is encoded by the HSPE1 gene. The homolog in E. coli is GroES that is a chaperonin which usually works in conjunction with GroEL.

Structure and function

GroES exists as a ring-shaped oligomer of between six and eight identical subunits, while the 60 kDa chaperonin (cpn60, or groEL in bacteria) forms a structure comprising 2 stacked rings, each ring containing 7 identical subunits. These ring structures assemble by self-stimulation in the presence of Mg2+-ATP. The central cavity of the cylindrical cpn60 tetradecamer provides an isolated environment for protein folding whilst cpn-10 binds to cpn-60 and synchronizes the release of the folded protein in an Mg2+-ATP dependent manner. The binding of cpn10 to cpn60 inhibits the weak ATPase activity of cpn60.

Escherichia coli GroES has also been shown to bind ATP cooperatively, and with an affinity comparable to that of GroEL. Each GroEL subunit contains three structurally distinct domains: an apical, an intermediate and an equatorial domain. The apical domain contains the binding sites for both GroES and the unfolded protein substrate. The equatorial domain contains the ATP-binding site and most of the oligomeric contacts. The intermediate domain links the apical and equatorial domains and transfers allosteric information between them. The GroEL oligomer is a tetradecamer, cylindrically shaped, that is organised in two heptameric rings stacked back to back. Each GroEL ring contains a central cavity, known as the `Anfinsen cage', that provides an isolated environment for protein folding.