Protein Sequence Editing of SKN-1A/Nrf1 by Peptide:N-Glycanase Controls Proteasome Gene Expression

Abstract

Graphical Abstract Highlights d PNGase edits glycosylated Asn residues of the SKN-1A transcription factor to Asp d These edits are required for SKN-1A to regulate proteasome subunit genes d Sequence-edited SKN-1A enhances proteostasis d Edits cause ER-targeted and cytosolic SKN-1 isoforms to regulate distinct genes SUMMARYThe proteasome mediates selective protein degradation and is dynamically regulated in response to proteotoxic challenges. SKN-1A/Nrf1, an endoplasmic reticulum (ER)-associated transcription factor that undergoes N-linked glycosylation, serves as a sensor of proteasome dysfunction and triggers compensatory upregulation of proteasome subunit genes. Here, we show that the PNG-1/NGLY1 peptide:N-glycanase edits the sequence of SKN-1A protein by converting particular N-glycosylated asparagine residues to aspartic acid. Genetically introducing aspartates at these N-glycosylation sites bypasses the requirement for PNG-1/NGLY1, showing that protein sequence editing rather than deglycosylation is key to SKN-1A function. This pathway is required to maintain sufficient proteasome expression and activity, and SKN-1A hyperactivation confers resistance to the proteotoxicity of human amyloid beta peptide. Deglycosylationdependent protein sequence editing explains how ER-associated and cytosolic isoforms of SKN-1 perform distinct cytoprotective functions corresponding to those of mammalian Nrf1 and Nrf2. Thus, we uncover an unexpected mechanism by which N-linked glycosylation regulates protein function and proteostasis.

ADrosophilanatural variation screen identifies NKCC1 as a substrate of NGLY1 deglycosylation and a modifier of NGLY1 deficiency

“…During this proteasome stress, NRF1 20 accumulates and is deglycosylated by NGLY1 (Tomlin et al, 2017). Rather than targeting the 21 protein for degradation, the deglycosylation activates NRF1 by converting asparagine to aspartic 22 acid residues (Lehrbach, Breen, & Ruvkun, 2019). NRF1 can then be imported into the nucleus 23 to act as a transcription factor for proteasome subunits.…”

Functional glycomics: Application to medical science and hepatology

“…NGLY1 is a cytosolic deglycosylating enzyme that acts on misfolded N ‐glycoproteins destined for proteasomal degradation . Additionally, recent evidence suggested that NGLY1 is also involved in the activation of nuclear factor erythroid‐2‐like 1 (NFE2L1), a transcription factor important for stress responses . It is therefore tempting to speculate that a defect of NFE2L1 activation (or, if any, other Ngly1‐dependent molecules) might be the underlying molecular cause of the shared clinical features among these genetic disorders, as defects of either N‐ glycosylation or Ngly1 will result in defective activation of NFE2L1 (Fig.…”

“…This common lack of NFE2L1 activation (and possibly other molecules that are activated through similar reactions) might represent the molecular mechanism underlying the similar clinical features between some CDGs and NGLY1 deficiency. Figures based on references . [Color figure can be viewed at wileyonlinelibrary.com]…”

A unity of opposites in between Nrf1- and Nrf2-mediated responses to the endoplasmic reticulum stressor tunicamycin

“…Moreover, additional homologue SKN-1A associated with the ER of Caenorhabditis elegans also mediates a cytoplasmic unfolded protein response and promotes longevity [48]. This biological event occurs to be regulated by the amino acid sequence editing of SKN-1A by NGLY1 from its glycosylated Asn (-N-S/T-) into acidic Asp (-D-S/T-) residues within this protein, in order to control expression of PSM genes against proteotoxic stress [49]. Overall, these supportive findings are prime to confirm our prior work on Nrf1 glycosylation and deglycosylation to finely tune its transactivation activity [20,33,50,51].…”