SUBUNIT ARRANGEMENT IN THE HUMAN 20S PROTEASOME

In human 20S proteasomes two copies of each of seven different Lu-type and seven different P-type subunits are assembled to form a stack of four seven-membered rings, giving the general structure alpha(1-7), be ta(1-7), beta(1-7), alpha(1-7). By means of immunoelectron microscopy and chemical crosslinking of neighboring: subunits,,ve have determined the positions of the individual subunits in the proteasome. The topog raphy shows that for the trgpsin-like, the chymotrypsin-like, and the postglutamyl cleaving activities, the pairs of beta type subunits, whi ch are thought to form active sites, are nearest neighbors.