Function and regulation of the Cdc48-20S proteasome
Final Report Abstract
Proteasomes are large macromolecular complexes that execute ATP-dependent protein degradation during protein quality control and regulate various cell signaling pathways. These protein machines consist of the selfcompartmentalized 20S peptidase capped on one or both sides by a hexameric AAA+ ATPase unfolding rings. Studies over the last decades had established the dogma that in archaea the 20S peptidase exclusively interacts with the PAN AAA+ unfoldase, whereas in eukaryotes 20S exclusively binds to the 19S regulatory particle to form the 26S proteasome. This dogma had been transformed by my discovery of the archaeal Cdc4820S proteasome. Cdc48 (alias p97/VCP) is a highly abundant, essential and evolutionarily conserved type II AAA+ ATPase that controls numerous biological processes including membrane fusion, cell-cycle regulation, and protein degradation by autophagy and by the ubiquitin-proteasome-system. Key questions about the modus operandi and the physiological function of the newly identify Cdc4820S proteasome remain to be answered. Here, I revealed the structural architecture of the archaeal Cdc4820S proteasome by electron microscopy and explored the molecular mechanisms that allow Cdc48 to interact the proteasomal 20S peptidase. Beside the previously identified HbYX motif (a C-terminal peptides sequence), I discovered that Cdc48 uses a near-axial pore-2 loop motif to bind 20S. Similar interactions might also stabilize other AAA+ proteases including the 26S proteasome. These motifs are also conserved in eukaryotic Cdc48, which still maintains the ability to directly bind and communicate with its cognate 20S peptidase. Importantly, some patients with familial ALS, an ultimately fatale disease affecting protein quality control, contain mutations in the pore-2 loop motif of Cdc48. I found that these disease alleles of Cdc48 severely impair direct 20S binding and proteolytic communication and potentially therefore lead to accumulation of ubiquitinated protein aggregates and cellular proteotoxicity. In conclusion, my studies provide important novel insights into how this ancient AAA+ protease works to execute intracellular proteolysis and how its function/malfunction can contribute to development of human diseases.
Publications
- (2014). Architecture and assembly of the archaeal Cdc48•20S proteasome. Proc. Natl. Acad. Sci. 111(17):E1687–E1694
Barthelme, D., Chen, CJ., Grabenstatter, J., Baker, TA., and Sauer, RT.
(See online at https://doi.org/10.1073/pnas.1404823111)
