Control of glycosylation of MHC class II-associated invariant chain by translocon-associated RAMP4

EMBO J. 1999 Sep 1;18(17):4804-15. doi: 10.1093/emboj/18.17.4804.

Abstract

Protein translocation across the membrane of the endoplasmic reticulum (ER) proceeds through a proteinaceous translocation machinery, the translocon. To identify components that may regulate translocation by interacting with nascent polypeptides in the translocon, we used site-specific photo-crosslinking. We found that a region C-terminal of the two N-glycosylation sites of the MHC class II-associated invariant chain (Ii) interacts specifically with the ribosome-associated membrane protein 4 (RAMP4). RAMP4 is a small, tail-anchored protein of 66 amino acid residues that is homologous to the yeast YSY6 protein. YSY6 suppresses a secretion defect of a secY mutant in Escherichia coli. The interaction of RAMP4 with Ii occurred when nascent Ii chains reached a length of 170 amino acid residues and persisted until Ii chain completion, suggesting translocational pausing. Site-directed mutagenesis revealed that the region of Ii interacting with RAMP4 contains essential hydrophobic amino acid residues. Exchange of these residues for serines led to a reduced interaction with RAMP4 and inefficient N-glycosylation. We propose that RAMP4 controls modification of Ii and possibly also of other secretory and membrane proteins containing specific RAMP4-interacting sequences. Efficient or variable glycosylation of Ii may contribute to its capacity to modulate antigen presentation by MHC class II molecules.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Antigens, Differentiation, B-Lymphocyte / metabolism*
  • DNA, Complementary / metabolism
  • Glycosylation
  • Histocompatibility Antigens Class II / metabolism*
  • Humans
  • Membrane Proteins / metabolism*
  • Mice
  • Models, Biological
  • Molecular Sequence Data
  • Mutagenesis
  • Precipitin Tests
  • Protein Binding
  • Protein Biosynthesis
  • Rats
  • Ribosomes / metabolism*
  • Sequence Homology, Amino Acid
  • Time Factors

Substances

  • Antigens, Differentiation, B-Lymphocyte
  • DNA, Complementary
  • Histocompatibility Antigens Class II
  • Membrane Proteins
  • Serp1 protein, rat
  • invariant chain

Associated data

  • GENBANK/AJ238236