Is the eukaryotic cis‐prenyltransferase a heteromer? The role of NgBR and its yeast ortholog Nus1 in protein glycosylation

Abstract

Dolichyl phosphate (Dol‐P) serves as an obligate lipid carrier in different type of protein glycosylations. Dol‐P precursor ‐ polyprenyl pyrophosphate ‐ is synthesized by a cis‐prenyltransferase (cisPTase) activity. Recently we have shown that NgBR is as an essential component of the Dol‐P biosynthetic machinery. Loss of NgBR results in deficit of cisPTase activity, leading to diminished levels of dolichol‐linked oligosaccharides and a reduction in protein N‐glycosylation. NgBR interacts with the previously identified cisPTase hCIT, enhances hCIT protein stability, and promotes Dol‐P synthesis. Inactivation of yeast ortholog of NgBR, Nus1 gives lethal phenotype and causes N‐glycosylation defect. In this work we confirmed that shutting down expression of NUS1 results in N‐glycosylation defect and demonstrated that this phenotype is related to loss of cisPTase activity and dolichol synthesis. Glycosylation‐dependent phenotypes are complemented by expression of bacterial type undecaprenyl pyrophosphate synthase. We hypothesize that active eukaryotic cisPTase is not a homodimer as crystallized bacterial enzyme but heteromer consisting of: NgBR and hCIT in humans or Nus1 and Rer2 in ER and Nus1 and Srt1 in lipids bodies of yeast S. cerevisiae. Reconstitution of active eukaryotic cisPTase is in progress.This work was supported by grant R01HL081190 from the NIH to WCS