Subunit arrangement in the human 20S proteasome

Subunit arrangement in the human 20S proteasome

^*Diabetes Forschungsinstitut, Auf’m Hennekamp 65, D-40225 Düsseldorf, Germany; and ^†August Krogh Institute, University of Copenhagen, Universitetsparken 13, DK-2100 Copenhagen Ø, Denmark

Abstract

In human 20S proteasomes two copies of each of seven different α-type and seven different β-type subunits are assembled to form a stack of four seven-membered rings, giving the general structure α_1–7, β_1–7, β_1–7, α_1–7. By means of immunoelectron microscopy and chemical crosslinking of neighboring subunits, we have determined the positions of the individual subunits in the proteasome. The topography shows that for the trypsin-like, the chymotrypsin-like, and the postglutamyl cleaving activities, the pairs of β type subunits, which are thought to form active sites, are nearest neighbors.

Footnotes

↵ ‡ To whom reprint requests should be addressed.
Hans H. Ussing, University of Copenhagen, Copenhagen, Denmark
ABBREVIATIONS:

PGPH,

peptidylglutamyl peptide hydrolyzing;

sulfo-EGS,

ethyleneglycol bis(sulfosuccinimidyl-succinate);

DSP,

dithiobis(succinimidylpropionate)