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Three-dimensional structure of transporter associated with antigen processing (TAP) obtained by single Particle image
G Velarde1, R C Ford, M F Rosenberg
1Department of Biomolecular Sciences, UMIST, Manchester M60 1QD, United Kingdom.
The Journal of Biological Chemistry
|October 12, 2001
Summary
The transporter associated with antigen processing (TAP) structure was revealed using electron microscopy. This ATP binding cassette transporter plays a key role in the immune system by moving peptides into the endoplasmic reticulum.
Area of Science:
- Molecular biology
- Immunology
- Structural biology
Background:
- The transporter associated with antigen processing (TAP) is crucial for the adaptive immune response.
- TAP facilitates peptide translocation into the endoplasmic reticulum for MHC class I assembly.
- Understanding TAP structure is key to elucidating antigen presentation pathways.
Purpose of the Study:
- To determine the structural characteristics of the TAP complex.
- To visualize the TAP1 and TAP2 subunits and their arrangement within the transporter.
- To compare the structure of TAP with other ATP binding cassette (ABC) transporters.
Main Methods:
- Immunoaffinity purification of TAP particles (TAP1+2 and TAP2 alone).
- Detergent solubilization of purified TAP complexes.
- Electron microscopy for projection and 3D structure determination.
Main Results:
- Projection structures of TAP1+2 particles showed a ~10 nm molecule with a central region.
- TAP2 particles were smaller in projection.
- 3D structure revealed TAP as a single heterodimeric complex with a 3 nm lumenal pocket formed by TAP1 and TAP2 subunits.
Conclusions:
- The TAP complex forms a distinct heterodimeric structure.
- The identified structure provides insights into the mechanism of peptide translocation.
- TAP shares structural similarities with other ABC transporters, suggesting a common evolutionary origin and tertiary structure.