K48-ubiquitin-dependent proteases cut-up post-ER proteins

Area of Science:

• Cell Biology
• Molecular Biology
• Protein Degradation

Background:

• Polyubiquitin chains regulate protein degradation in the secretory system.
• The functional differences between K48 and K63 ubiquitin linkages for membrane proteins are not fully understood.

Purpose of the Study:

• To investigate the distinct roles of K48 and K63 polyubiquitin chains in directing post-endoplasmic reticulum (ER) protein degradation.
• To identify the proteases involved in these distinct degradation pathways.

Main Methods:

• Analysis of post-ER protein sorting and degradation based on ubiquitination.
• Characterization of ubiquitin-dependent proteases Ddi1 and Rbd2.
• Biochemical assays to study Ddi1's catalytic activity and ubiquitin binding.

Main Results:

• K63-linked polyubiquitination sorts proteins to multivesicular bodies (MVBs) for lysosomal degradation.
• K48-linked polyubiquitination leads to membrane protein shearing and proteasomal degradation.
• Ddi1 and Rbd2 are identified as key proteases in these distinct degradation pathways, termed CUT-UP.

Conclusions:

• Polyubiquitin chain linkage isomers (K48 vs. K63) encode specific degradative fates for post-ER proteins.
• Ddi1 and Rbd2 represent novel ubiquitin-dependent proteases targeting integral membrane proteins.