Understanding How Proteins are Extracted from the Lectin Chaperone Cycle for Degradation

Presenter

Liza Pobezinskaya

Campus

UMass Amherst

Sponsor

Daniel N. Hebert, Department of Biochemistry and Molecular Biology, UMass Amherst

Schedule

Session 4, 2:30 PM - 3:15 PM [Schedule by Time][Poster Grid for Time/Location]

Location

Poster Board C16, Poster Showcase Room (163), Row 2 (C11-C20) [Poster Location Map]

Abstract

One third of the human proteome is targeted to the secretory pathway and translocated into the endoplasmic reticulum (ER). This organelle provides the environment necessary for the proper folding of proteins prior to trafficking. Many clients of the secretory pathway are appended with carbohydrates, known as N-linked glycans that act as quality control tags. These glycans are added co- or post-translationally and rapidly modified to allow the protein to bind the lectin chaperones, calnexin and calreticulin. These chaperones provide additional folding assistance as the protein attempts to reach its native form. If successful, the protein can continue trafficking. However, if remaining non-native it can be recognized by the key quality control enzyme, UGGT, which modifies the glycan allowing the substrate to re-enter the cycle for further folding assistance. After futile rounds of folding, the protein is degraded to maintain homeostasis. One commonly used pathway for glycoproteins is the ER associated degradation pathway (ERAD), which is initiated by further trimming of N-glycans by ER resident mannosidases. The responsible mannosidases for extracting proteins from the chaperone cycle remains unclear. To address this, we expressed known ERAD clients in CRISPR modified cell lines and followed lectin chaperone binding using established assays. Protein:lectin binding was visualized by Western blot from the various knockout cell lines, showing two ER mannosidases as promising candidates. This work has provided additional insight on how proteins are degraded and trafficked through the ER. A better understanding is crucial for addressing protein folding diseases stemming from inefficient misfolding protein degradation. 

Keywords

Protein degradation , ER degradation mechanisms, ER mannosidase involvement

Research Area

Genetics

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