A 13-amino acid peptide in three yeast glycosyltransferases may be involved in dolichol recognition.

A 13-amino acid peptide was identified in three glycosyltransferases of the yeast endoplasmic reticulum. These enzymes, the products of the ALG1, ALG7, and DPM1 genes, catalyze the transfer of sugars from nucleotide sugars to dolichol phosphate derivatives. The consensus sequence for the conserved peptide was Leu-Phe-Val-Xaa-Phe-Xaa-Xaa-Ile-Pro-Phe-Xaa-Phe-Tyr. A sequence resembling the conserved peptide was also found in the predicted SEC59 protein, which is suspected to participate in assembly of the lipid-linked precursor oligosaccharide, although its specific function is unknown. All of the identified sequences contain an isoleucine at position 8 and phenylalanine or tyrosine at positions 2, 5, and 12. We believe this peptide may be involved in dolichol recognition for the following reasons. (i) The conserved sequence occurs in potential membrane-spanning regions. (ii) The ALG7 and DPM1 proteins are known to recognize the isoprenoid region of dolichol phosphate specifically; this recognition presumably occurs in the membrane since dolichol is very hydrophobic. (iii) The consensus sequence is similar to a region of two halobacterial proteins implicated in binding of the isoprenoid region of retinal. (iv) If the consensus sequence is represented as an alpha-helix, the conserved residues lie on one face of the helix. An alpha-helical structure is likely since the conserved regions are in potential membrane-spanning domains.