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Identification of two distinct intracellular localization signals in STT3-B.

Caron E, Côté C, Parisien M, Major F, Perreault C

Institute of Research in Immunology and Cancer, University of Montreal, CP 6128, Downtown Station, Montreal, Que., Canada H3C 3J7.

The STT3 subunit of the oligosaccharyltransferase complex plays a critical role in the N-glycosylation process. From Arabidopsis thaliana to Homo sapiens, two functional STT3 isoforms have been identified, STT3-A and STT3-B. We report that the last transmembrane (TM) segment of STT3-B corresponds to a topogenic determinant that is sufficient for proper integration and orientation of STT3-B C-terminal domain. Notably, the last TM segment of STT3-A and -B isoforms present major differences in amino acid sequence and predicted 3D structure. We also identified a bipartite nuclear targeting sequence in the C-terminal tail of STT3-B that is absent in STT3-A. The latter sequence is sufficient to induce nucleolar localization of a reporter protein. Our results show that STT3-A and -B display two structural differences that may have a drastic influence on their function and might account for the remarkable evolutionary conservation of the two STT3 paralogs.

Arch. Biochem. Biophys. 2006;445(1):108-14.

Pubmed ID: 16297371

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