Membrane topology of the ATP binding cassette transporter ABCR and its relationship to ABC1 and related ABCA transporters: identification of N-linked glycosylation sites

J Biol Chem. 2001 Jun 29;276(26):23539-46. doi: 10.1074/jbc.M101902200. Epub 2001 Apr 24.


ABCR is a member of the ABCA subclass of ATP binding cassette transporters that is responsible for Stargardt macular disease and implicated in retinal transport across photoreceptor disc membranes. It consists of a single polypeptide chain arranged in two tandem halves, each having a multi-spanning membrane domain followed by a nucleotide binding domain. To delineate between several proposed membrane topological models, we have identified the exocytoplasmic (extracellular/lumen) N-linked glycosylation sites on ABCR. Using trypsin digestion, site-directed mutagenesis, concanavalin A binding, and endoglycosidase digestion, we show that ABCR contains eight glycosylation sites. Four sites reside in a 600-amino acid exocytoplasmic domain of the N-terminal half between the first transmembrane segment H1 and the first multi-spanning membrane domain, and four sites are in a 275-amino acid domain of the C half between transmembrane segment H7 and the second multi-spanning membrane domain. This leads to a model in which each half has a transmembrane segment followed by a large exocytoplasmic domain, a multi-spanning membrane domain, and a nucleotide binding domain. Other ABCA transporters, including ABC1 linked to Tangier disease, are proposed to have a similar membrane topology based on sequence similarity to ABCR. Studies also suggest that the N and C halves of ABCR are linked through disulfide bonds.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • ATP Binding Cassette Transporter 1
  • ATP-Binding Cassette Transporters / chemistry*
  • ATP-Binding Cassette Transporters / genetics
  • ATP-Binding Cassette Transporters / metabolism
  • Amino Acid Sequence
  • Animals
  • COS Cells
  • Cattle
  • Concanavalin A / metabolism
  • Consensus Sequence
  • Disulfides / metabolism
  • Glycoproteins / chemistry*
  • Glycosylation
  • Humans
  • Models, Biological
  • Molecular Sequence Data
  • Protein Structure, Tertiary
  • Rod Cell Outer Segment / metabolism
  • Sequence Deletion
  • Sequence Homology, Amino Acid
  • Transfection
  • Trypsin / chemistry


  • ABCA1 protein, human
  • ABCA4 protein, human
  • ATP Binding Cassette Transporter 1
  • ATP-Binding Cassette Transporters
  • Disulfides
  • Glycoproteins
  • Concanavalin A
  • Trypsin