Two oligosaccharyl transferase complexes exist in yeast and associate with two different translocons

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Oligosaccharyl transferase (OT) is crucial for N-linked glycosylation in the endoplasmic reticulum (ER).
• The precise composition and subunit interactions within the OT complex have been debated.
• Understanding OT complex assembly is key to elucidating protein processing in the ER.

Purpose of the Study:

• To investigate the oligomeric state of yeast OT subunits.
• To determine the composition of the OT complex and identify potential isoforms.
• To explore the interactions between OT isoforms and translocon complexes.

Main Methods:

• Utilized a membrane protein two-hybrid approach (split-ubiquitin system) in Saccharomyces cerevisiae.
• Performed genetic and biochemical assays to characterize Ost3p and Ost6p.
• Employed blue native gel electrophoresis to analyze OT complex composition in wild-type and mutant yeast strains.

Main Results:

• Most OT subunits exist as dimers or oligomers in yeast.
• Ost3p and Ost6p exhibit similar behaviors but do not co-exist in the same OT complex.
• Evidence suggests two distinct OT isoforms, differing by Ost3p or Ost6p.
• Each OT isoform specifically interacts with either the Sec61 or Ssh1 translocon complex.

Conclusions:

• The yeast OT complex exists in at least two distinct isoforms.
• These isoforms differ in their subunit composition, specifically the presence of Ost3p or Ost6p.
• Each OT isoform exhibits specific interactions with different translocon complexes (Sec61 and Ssh1).
• This isoform-specific interaction suggests distinct roles in protein translocation and glycosylation pathways.