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- Title
Alg14 organizes the formation of a multiglycosyltransferase complex involved in initiation of lipid-linked oligosaccharide biosynthesis.
- Authors
Lu, Jishun; Takahashi, Tetsuo; Ohoka, Atsuko; Nakajima, Kei-ichi; Hashimoto, Ryo; Miura, Nobuaki; Tachikawa, Hiroyuki; Gao, Xiao-Dong
- Abstract
Protein N-glycosylation begins with the assembly of a lipid-linked oligosaccharide (LLO) on the endoplasmic reticulum (ER) membrane. The first two steps of LLO biosynthesis are catalyzed by a functional multienzyme complex comprised of the Alg7 GlcNAc phosphotransferase and the heterodimeric Alg13/Alg14 UDP-GlcNAc transferase on the cytosolic face of the ER. In the Alg13/14 glycosyltransferase, Alg14 recruits cytosolic Alg13 to the ER membrane through interaction between their C-termini. Bioinformatic analysis revealed that eukaryotic Alg14 contains an evolved N-terminal region that is missing in bacterial orthologs. Here, we show that this N-terminal region of Saccharomyces cerevisiae Alg14 localize its green fluorescent protein fusion to the ER membrane. Deletion of this region causes defective growth at 38.5°C that can be partially complemented by overexpression of Alg7. Coimmunoprecipitation demonstrated that the N-terminal region of Alg14 is required for direct interaction with Alg7. Our data also show that Alg14 lacking the N-terminal region remains on the ER membrane through a nonperipheral association, suggesting the existence of another membrane-binding site. Mutational studies guided by the 3D structure of Alg14 identified a conserved α-helix involved in the second membrane association site that contributes to an integral interaction and protein stability. We propose a model in which the N- and C-termini of Alg14 coordinate recruitment of catalytic Alg7 and Alg13 to the ER membrane for initiating LLO biosynthesis.
- Subjects
OLIGOSACCHARIDES; BIOSYNTHESIS; GLYCOSYLATION; PHOSPHOTRANSFERASES; MULTIENZYME complexes; BIOINFORMATICS
- Publication
Glycobiology, 2012, Vol 22, Issue 4, p504
- ISSN
0959-6658
- Publication type
Article