BINDING OF AMYLOID-BETA PROTEIN TO THE 20 S PROTEASOME

Neurodegenerative disorders of aging are characterized by the intraneu ronal accumulation of ubiquitin conjugates into tangles and inclusions . Ubiquitin conjugates are degraded by cellular particles known as pro teasomes. We have previously shown that amyloid beta protein (A beta) inhibits proteasomal activity and thereby blocks ubiquitin conjugate d egradation. In the present studies, we found that A beta binds the 20 S proteasome and forms a proteasome-A beta complex. The complex was de tected by Western blot with anti-A beta antibodies. Using a 1.4 nm Nan ogold-labeled A beta, we visualized proteasome-A beta complexes by sca nning transmission electron microscopy (STEM). Analysis of the side-on oriented proteasome-A beta complexes revealed a single gold particle, corresponding to one gold-labeled A beta, in the middle portion of th e proteasome. On end-on views of proteasome-A beta complexes, gold was detected within the area delimited by the proteasome circular project ion. Both STEM views are consistent with A beta localization inside th e proteasome along the peptide channel. Direct interaction of A beta w ith the inner catalytic compartment of the proteasome may explain the generation of ubiquitin-containing lesions in Alzheimer's disease and other neurodegenerative disorders. In addition, detection of Nanogold- labeled peptide inside the 20 S eukaryotic proteasome suggests that co nformational constraints for protein degradation in eukaryotic proteas omes are different from those in archaebacteria proteasomes.