Figure 1.

Chemical structure of the proteasome inhibitor bortezomib: pyrazylcarbonyl-Phe-Leu-boronate (A). Schematic illustration of the ubiquitin-proteasome pathway. Misfolded proteins (e.g., p53) are targeted for degradation by the 26S proteasome via phosporylation and ubiquitination (B). Following substrate degradation, the ubiquitin tags and peptides are recycled for future use.