The proteasome, a validated anticancer
target, participates in
an array of biochemical activities, which range from the proteolysis
of defective proteins to antigen presentation. We report the preparation
of biochemically and photophysically distinct green, red, and far-red
real-time sensors designed to simultaneously monitor the proteasome’s
chymotrypsin-, trypsin-, and caspase-like activities, respectively.
These sensors were employed to assess the effect of simultaneous multiple
active site catalysis on the kinetic properties of the individual
subunits. Furthermore, we have found that the catalytic signature
of the proteasome varies depending on the source, cell type, and disease
state. Trypsin-like activity is more pronounced in yeast than in mammals,
whereas chymotrypsin-like activity is the only activity detectable
in B-cells (unlike other mammalian cells). Furthermore, chymotrypsin-like
activity is more prominent in transformed B cells relative to their
counterparts from healthy donors
