Asparagine-linked glycosylation is an essential and highly conserved protein modification reaction that occurs in the endoplasmic reticulum of cells during protein synthesis at the ribosome. In the central reaction, a pre-assembled high-mannose sugar is transferred from a lipid-linked donor substrate to the side-chain of an asparagine residue in an -N-X-T/S- sequence (where X is any residue except proline). This reaction is carried by a membrane-bound multi-subunit enzyme complex, oligosaccharyltransferase (OST). In humans, genetic defects in OST lead to a group of rare metabolic diseases collectively known as Congenital Disorders of Glycosylation. Certain mutations are lethal for all organisms. In yeast, the OST is composed of nine non-identical protein subunits. The functional enzyme complex contains eight subunits with either Ost3 or Ost6 at any given time. Ost4, an unusually small protein, plays a very important role in the stabilization of the OST complex. It bridges the catalytic subunit Stt3 with Ost3 (or Ost6) in the Stt3-Ost4-Ost3 (or Ost6) sub-complex. Mutation of any residue from M18-I24 in the trans-membrane helix of yeast Ost4 negatively impacts N-linked glycosylation and the growth of yeast. Indeed, mutation of valine23 to an aspartate impairs OST function in vivo resulting in a lethal phenotype in yeast. To understand the structural mechanism of Ost4 in the stabilization of the enzyme complex, we have initiated a detailed investigation of Ost4 and its functionally important mutant, Ost4V23D. Here, we report the backbone ¹H, ¹³C, and ¹⁵N resonance assignments for Ost4 and Ost4V23D in dodecylphosphocholine micelles.

• PMID: 32328881
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Journal Article | Research Support, Non-U.S. Gov't | Research Support, U.S. Gov't, Non-P.H.S.

Authors

Chaudhary BP, Zoetewey D, Mohanty S

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