Lysine Can Be Replaced by Histidine but Not by Arginine as the ER Retrieval Motif for Type I Membrane Proteins

• Published in: Biochemical and biophysical research communications Vol. 291; no. 4; pp. 751 - 757
• Main Authors: Hardt, Birgit, Bause, Ernst
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 08.03.2002
• Subjects: Amino Acid Motifs; Amino Acid Sequence; Amino Acid Substitution; Animals; Arginine - chemistry; Arginine - genetics; arginine motif; COS Cells; Endoplasmic Reticulum - chemistry; ER localisation; Hexosyltransferases; Histidine - chemistry; Histidine - genetics; histidine motif; Lysine - chemistry; Lysine - genetics; lysine motif; Membrane Proteins - chemistry; Membrane Proteins - genetics; Membrane Proteins - metabolism; Microscopy, Fluorescence; OST48; Protein Structure, Tertiary; Transferases - chemistry; Transferases - genetics; Transferases - metabolism; type I membrane protein; histidine motif; arginine motif; OST48; ER localisation; type I membrane protein; lysine motif
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1006/bbrc.2002.6515

The OST48 subunit of the oligosaccharyltransferase complex is a type I membrane protein containing three lysines in its cytosolic domain. The two lysines in positions 3 and 5 from the C-terminus are able to direct protein localisation within the endoplasmic reticulum (ER) by COPI-mediated retrieval. Substitution of these lysines by arginine resulted in cell-surface expression of OST48, whereas ER residency was maintained when either Lys-5 or Lys-3 but not both was replaced with arginine. Localisation of OST48 was not affected by substitution of the two lysines by histidine, indicating that a His-Xaa-His sequence, in contrast to Arg-Xaa-Arg, contains ER-specific targeting information. These differences show that simple charge interactions are not sufficient for ER retention and that other structural factors also play a role. The His-Xaa-His sequence could represent a new and independent signal for directing ER localisation differing from both the arginine motif in type II proteins and the lysine motif in type I proteins. Our data do not exclude, however, that the histidine sequence simply mimicks the lysine motif as a sorting signal, being recognised by and interacting with the same receptor subunit(s) in COP-I-coated vesicles. Conclusions arising from this assumption involving the conformation of lysine at the putative COP-I binding site and the failure of Arg-Xaa-Arg to mediate ER localisation for type I proteins are discussed.