Clustering of peptide-loaded MHC class I molecules for endoplasmic reticulum export imaged by fluorescence resonance energy transfer.

Department of Biology, Johns Hopkins University, Baltimore, MD 21218, USA.
The Journal of Immunology (Impact Factor: 5.36). 07/2001; 166(11):6625-32. DOI: 10.4049/jimmunol.166.11.6625
Source: PubMed

ABSTRACT Fluorescence resonance energy transfer between cyan fluorescent protein- and yellow fluorescent protein-tagged MHC class I molecules reports on their spatial organization during assembly and export from the endoplasmic reticulum (ER). A fraction of MHC class I molecules is clustered in the ER at steady state. Contrary to expectations from biochemical models, this fraction is not bound to the TAP. Instead, it appears that MHC class I molecules cluster after peptide loading. This clustering points toward a novel step involved in the selective export of peptide-loaded MHC class I molecules from the ER. Consistent with this model, we detected clusters of wild-type HLA-A2 molecules and of mutant A2-T134K molecules that cannot bind TAP, but HLA-A2 did not detectably cluster with A2-T134K at steady state. Lactacystin treatment disrupted the HLA-A2 clusters, but had no effect on the A2-T134K clusters. However, when cells were fed peptides with high affinity for HLA-A2, mixed clusters containing both HLA-A2 and A2-T134K were detected.

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