The reference OMIM entry for this protein is 611908

Rft1, s. cerevisiae, homolog of; rft1

DESCRIPTION

N-glycosylation of proteins follows a highly conserved pathway that begins with the synthesis of a Man(5)GlcNAc(2)-dolichylpyrophosphate (PP-Dol) intermediate on the cytoplasmic side of the endoplasmic reticulum (ER) membrane followed by the translocation of Man(5)GlcNAc (2)-PP-Dol to the luminal side of the ER membrane. RFT1 is the flippase enzyme that catalyzes this translocation (Helenius et al., 2002).

CLONING

By database searching with the sequence of S. cerevisiae Rft1 as query, followed by RT-PCR of human fibroblast total RNA, Haeuptle et al. (2008) cloned RFT1. The deduced 541-amino acid protein contains 11 transmembrane domains and has a potential N-glycosylation site in a hydrophilic loop within the ER lumen. RFT1 shares 22% sequence identity with the yeast protein.

GENE FUNCTION

Helenius et al. (2002) showed that the expression of yeast Rft1 complemented a defect in N-glycosylation in the delta-alg11 (613666) strain of yeast. Overexpression of Rft1 in delta-alg11 yeast suggested that Rft1 is the limiting component for the flipping of Man(5)GlcNAc(2)-PP-Dol from the cytoplasmic to luminal side of the ER membrane in vivo and that no additional factors are required. Rft1 depletion in yeast led to underglycosylation of the vacuolar N-linked glycoprotein carboxypeptidase Y. Haeuptle et al. (2008) found human RFT1 complemented Rft1-depletion in yeast and restored normal carboxypeptidase Y glycosylation.

MAPPING

Hartz (2008) mapped the RFT1 gene to chromosome 3p21.1 based on an alignment of the RFT1 sequence (GenBank GENBANK AJ318099) with the genomic sequence (build 36.1).

MOLECULAR GENETICS

A particular feature of N-glycans is that they are first assembled in the endoplasmic reticulum (ER) as lipid-linked oligosaccharides (LLO). This assembly proceeds through the sequential addition of monosaccharides to the growing LLO. The assembly of LLOs requires glycosyltransferases and their respective nucleotide- and dolicho-activated monosaccharide substrates, but it also requires several proteins that regulate the complex topology of the process. For example, in yeast the Rft1 protein is essential for translocation of the cytosolically oriented intermediate DolPP-GlcNAc(2)Man(5) into the ER lumen, where LLO assembly is completed. The identification of N-linked glycosylation disorders in humans, referred to as congenital disorders of glycosylation (see CDG1A, 212065), demonstrated the conservation of the LLO assembly pathway between yeast and humans. Haeuptle et al. (2008) identified a novel glycosylation defect in a theretofore untyped CDG case (CDG1N; 612015), thereby establishing the importance of the RFT1 protein in human N-linked glycosylation. The patient, who had been diagnosed with a disorder of N-linked glycosylation on the basis of detection of abnormal isoelectric focusing of serum transferrin, carried a homozygous point mutation in the RFT1 gene (R67C; 611908.0001). In 3 unrelated children with CDG1N, Vleugels et al. (2009) identified 3 different homozygous missense mutations in the RFT1 gene (611908.0001-611908.0003). All mutations were located in 1 of the hydrophilic loops predicted to be within the ER lumen. Patient fibroblasts showed accumulation of Man(5)GlcNAc(2)-PP-dolichol and decreased DNase I secretion compared to controls, and these defects were restored by expression of wildtype RFT1. In 2 unrelated children with CDG1N, Jaeken et al. (2009) identifie ... More on the omim web site

Subscribe to this protein entry history

Feb. 23, 2019: Protein entry updated
Automatic update: model status changed

Oct. 20, 2018: Protein entry updated
Automatic update: OMIM entry 611908 was added.

Oct. 19, 2018: Additional information
Initial protein addition to the database. This entry was referenced in Bryk and co-workers. (2017).