PMID: 24685145

Authors:

Mohorko E, Owen RL, Malojcic G, Brozzo MS, Aebi M, Glockshuber R

Title:

Structural basis of substrate specificity of human oligosaccharyl transferase subunit n33/tusc3 and its role in regulating protein N-glycosylation.

Journal:

Structure. 2014 Apr 8;22(4):590-601. doi: 10.1016/j.str.2014.02.013. Epub 2014, Mar 27.

Abstract:

N-linked glycosylation of proteins in the endoplasmic reticulum (ER) is essential in eukaryotes and catalyzed by oligosaccharyl transferase (OST). Human OST is a hetero-oligomer of seven subunits. The subunit N33/Tusc3 is a tumor suppressor candidate, and defects in the subunit N33/Tusc3 are linked with nonsyndromic mental retardation. Here, we show that N33/Tusc3 possesses a membrane-anchored N-terminal thioredoxin domain located in the ER lumen that may form transient mixed disulfide complexes with OST substrates. X-ray structures of complexes between N33/Tusc3 and two different peptides as model substrates reveal a defined peptide-binding groove adjacent to the active site that can accommodate peptides in opposite orientations. Structural and biochemical data show that N33/Tusc3 prefers peptides bearing a hydrophobic residue two residues away from the cysteine forming the mixed disulfide with N33/Tusc3. Our results support a model in which N33/Tusc3 increases glycosylation efficiency for a subset of human glycoproteins by slowing glycoprotein folding.