CSB Cutting Lecture Series, Professor Andy Martin, October 20, Munzer!
The Department of Chemical and Systems Biology Presents
Andy Martin, Ph.D.
Investigator, Howard Hughes Medical Institute
Professor of Biochemistry, Biophysics & Structural Biology
Department of Molecular & Cell Biology; QB3 Institute
University of California at Berkeley
Friday, October 20, 2023
12:30 PM – 1:30 PM (Pacific Time)
Munzer Auditorium
“Illuminating substrate processing by the 26S proteasome and the Cdc48/p97 protein unfoldase”
Abstract: Protein degradation by the ubiquitin-proteasome system (UPS) plays vital roles in all eukaryotic cells and involves several well-coordinated steps whose mechanistic elucidation is essential for our understanding of protein quality control, homeostasis, the regulatory functions of the UPS, and potential therapeutic interventions.
Our engineered systems for the incorporation of unnatural amino acids and single-molecule fluorescence measurements allow us to illuminate the proteasome mechanisms in unprecedented detail. Monitoring individual substrates during their passage through the proteasome central channel provides insights into the kinetics and coordination of processing steps, the mechanisms of hexameric AAA+ ATPase motors, and the principles for substrate selection and prioritization. Single-molecule FRET-based measurements with dual-labeled proteasomes reveal the conformational dynamics of the proteasome and how substrate-attached ubiquitin chains allosterically regulate degradation.
Interestingly, well-folded ubiquitinated proteins cannot be directly degraded by the proteasome, but need to be pre-processed by the AAA+ ATPase Cdc48/p97 in complex with the heterodimeric cofactor Ufd1/Npl4. Cdc48 initiates substrate unfolding by engaging the ubiquitin chain itself, and FRET-based assays in a reconstituted in vitro system allowed us to reveal the underlying mechanisms and kinetics, as well as the origin of Cdc48’s specificity for K48-linked ubiquitin chains.
As an alternative to ubiquitin, substrates can also be targeted for proteasomal degradation through the attachment of ubiquitin-like modifiers, including FAT10 in immune cells. We recently elucidated how the interferon-inducible cofactor Nub1 acts as a chaperone that traps partially unfolded states of FAT10 for proteasomal engagement and degradation in a novel mode of ubiquitin- and p97-independent substrate delivery.