Molecular architecture of the TAP-associated MHC class I peptide-loading complex

Elke Rufer; Ralf M Leonhardt; Michael R Knittler

doi:10.4049/jimmunol.179.9.5717

Molecular architecture of the TAP-associated MHC class I peptide-loading complex

J Immunol. 2007 Nov 1;179(9):5717-27. doi: 10.4049/jimmunol.179.9.5717.

Authors

Elke Rufer¹, Ralf M Leonhardt, Michael R Knittler

Affiliation

¹ Friedrich-Loeffler-Institute, Federal Research Institute for Animal Health, Institute of Immunology, Tuebingen, Germany.

PMID: 17947644
DOI: 10.4049/jimmunol.179.9.5717

Abstract

Tapasin organizes the peptide-loading complex (PLC) by recruiting peptide-receptive MHC class I (MHC-I) and accessory chaperones to the N-terminal regions of the TAP subunits TAP1 and TAP2. Despite numerous studies have shown that the formation of the PLC is essential to facilitate proper MHC-I loading, the molecular architecture of this complex is still highly controversial. We studied the stoichiometry of the PLC by blue native-PAGE in combination with Ab-shift assays and found that TAP/tapasin complexes exist at steady state as a mixture of two distinct oligomers of 350 and 450 kDa. Only the higher m.w. complex contains MHC-I and disulfide-linked tapasin/ER60 conjugates. Moreover, we show for the first time to our knowledge that the fully assembled PLC comprises two tapasin, two ER60, but only one complex of MHC-I and calreticulin. Based hereon we postulate that the TAP subunits alternate in the recruitment and loading of a single MHC-I.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

ATP Binding Cassette Transporter, Subfamily B, Member 2
ATP Binding Cassette Transporter, Subfamily B, Member 3
ATP-Binding Cassette Transporters / genetics
ATP-Binding Cassette Transporters / metabolism*
Alternative Splicing / genetics
Binding Sites
Calreticulin / metabolism
Cell Line
Dimerization
Disulfides / metabolism
Histocompatibility Antigens Class I / metabolism*
Humans
Membrane Transport Proteins / metabolism
Molecular Chaperones / metabolism
Peptides / metabolism*
Protein Binding
Protein Disulfide-Isomerases / metabolism
Type C Phospholipases / metabolism

Substances

ATP Binding Cassette Transporter, Subfamily B, Member 2
ATP Binding Cassette Transporter, Subfamily B, Member 3
ATP-Binding Cassette Transporters
Calreticulin
Disulfides
Histocompatibility Antigens Class I
Membrane Transport Proteins
Molecular Chaperones
Peptides
TAP1 protein, human
Tap1 protein, rat
Tap2 protein, rat
tapasin
TAP2 protein, human
Type C Phospholipases
Protein Disulfide-Isomerases