Date of Award

Fall 10-1-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Molecular Biophysics and Biochemistry

First Advisor

Schlieker, Christian

Abstract

Nodal modulator (NOMO) is a widely conserved type I transmembrane protein of unknown function, with three nearly identical orthologs specified in the human genome. We identified NOMO1 in a proteomics approach aimed at the identification of proteins that support the structural integrity of the endoplasmic reticulum (ER). We have investigated the role of NOMO1 in relation to ER morphology. Overexpression of NOMO1 imposes sheet morphology on the ER. Extending NOMO1 correlatively increases the ER intermembrane distance, demonstrating the ability to regulate the ER lumen distance. Depletion of NOMO1 and its orthologs causes a collapse of ER morphology concomitant with the formation of membrane-delineated holes in the ER network. These holes are positive for the lysosome marker LAMP1. LC3-II and p62 levels are increased upon NOMO depletion, indicative of upregulation or inhibition of autophagy. In vitro reconstitution of NOMO1 revealed a dimeric state that is mediated by the cytosolic tail domain, with each monomer featuring a “beads on a string” shape likely representing Ig-like folds. Based on these observations and a genetic epistasis analysis including the known ER-shaping proteins Atlastin2 and Climp63, we propose a role for NOMO1 in the functional network of ER-shaping proteins.

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