title: Beyond KDEL: the role of positions 5 and 6 in determining ER localization.
abstract: The C-terminal amino acid sequence of a protein plays an important role in determining the endoplasmic reticulum (ER) localization of many soluble proteins that enter the secretory pathway. While it is known that the four amino acids found at the extreme C-terminus of the protein (e.g., KDEL) play a critical role in the interaction with the receptors that mediate retrograde transport back to the ER, other factors within the protein are less well known. Here we show that positions -5 and -6 play an important role in determining the ER localization of soluble proteins, with the amino acids at these positions playing an essential role in ER localization of the human protein disulfide isomerase family member, ERp18. Three other naturally occurring C-terminal motifs were also found that work efficiently in ER localization as six-amino-acid variants, but inefficiently as the four-amino-acid variant. Using bimolecular fluorescence complementation, we demonstrate that positions -5 and -6 from the C-terminus of the protein play an important role in the recognition of KDEL-like ER retrieval motifs, with the three different human KDEL receptors showing different specificities for changes at these positions for both inefficient and efficient ER localization four-amino-acid motifs.
authors.affiliation: Department of Biochemistry, University of Oulu, Finland.
authors.forename: Heli I
authors.initials: HI
authors.lastname: Alanen
authors.forename: Irina B
authors.initials: IB
authors.lastname: Raykhel
authors.forename: Marja J
authors.initials: MJ
authors.lastname: Luukas
authors.forename: Kirsi E H
authors.initials: KE
authors.lastname: Salo
authors.forename: Lloyd W
authors.initials: LW
authors.lastname: Ruddock
mesh_terms: D000818:Animals; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D009842:Oligopeptides / Q000235:genetics / Q000378:metabolism*; D011490:Protein Disulfide Reductase (Glutathione) / Q000378:metabolism; D019704:Protein Disulfide-Isomerases / Q000502:physiology; D021382:Protein Sorting Signals / Q000235:genetics; D021381:Protein Transport; D018000:Receptors, Peptide / Q000235:genetics / Q000378:metabolism*
chemical_list: C064459:KDEL receptor; D009842:Oligopeptides; D021382:Protein Sorting Signals; D018000:Receptors, Peptide; C073762:lysyl-aspartyl-glutamyl-leucine; D011490:Protein Disulfide Reductase (Glutathione); C477009:TXNDC12 protein, human; D019704:Protein Disulfide-Isomerases