C-terminal sequence stability profiling in Saccharomyces cerevisiae reveals protective protein quality control...

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Protein quality control (PQC) maintains cellular health by eliminating misfolded or damaged proteins.
• The ubiquitin-proteasome system is a key PQC pathway, often targeting protein termini.
• C-terminal amino acid changes can result from various cellular processes, impacting protein stability.

Purpose of the Study:

• To investigate the role of C-terminal amino acid sequences in protein stability and degradation.
• To identify specific amino acid features that signal protein defects.
• To understand the evolutionary basis for C-terminal sequence selection in protein homeostasis.

Main Methods:

• Utilized a reporter protein system in budding yeast with light-controlled exposure of random C-terminal peptide collections (CtPC).
• Analyzed the impact of amino acid identity, position, and composition at C-terminal positions (-5 to -1) on protein stability.
• Investigated the involvement of specific PQC components, including ubiquitin-protein ligase Doa10 and SCF^Das1.

Main Results:

• Identified specific amino acid residues and sequence compositions at the C terminus that confer protein stability or instability.
• Demonstrated that these destabilizing C-terminal degrons (CtPC-degrons) are transferable between proteins.
• Observed evolutionary selection against destabilizing C-terminal residues in cytosolic and nuclear proteins.
• Showed that stop-codon read-through peptides often possess destabilizing C termini.

Conclusions:

• The C-terminal sequence is a critical determinant of protein stability and a target for PQC.
• A broad range of C-terminal sequence variants are recognized by PQC mechanisms, safeguarding the proteome.
• These findings reveal a sophisticated surveillance system for proteins with aberrant C termini.