T-cell Receptor and MHC Class I Complex
The T-cell receptor has some structural similarity to immunoglobulin Fab fragments, consisting of two chains each with an N-terminal immunoglobulin like variable (V) region and an immunoglobulin like constant (C) region. However the T-cell receptor functions to see antigen in the form of a small peptide expressed in the context of a Major Histocompatibility Complex (MHC) Class I or Class II molecule. The complex shown here is derived from the Brookhaven Protein Data Bank entry 1A07.pdb which is of a human MHC Class I, HLA-A 0201 molecule, with a peptide from Tax protein of human T-lymphotropic virus type 1, complexed with the terminal domains of a alpha/beta T-cell Receptor.
In the model shown the three extracellular domains of the MHC alpha chain are shown at the bottom in dark blue and the associated beta-2-microglobulin light chain in light blue. The alpha chain of the T-cell receptor is shown in yellow and the beta chain in red. For the T-cell receptor the Constant region domains are incomplete. From some angles it is possible to make out the end of the groove containing the peptide (green). It is clearly seen that the T-cell receptor is binding to an area comprising of the peptide and the the MHC.
It is interesting to compare this structure for a complex of T-cell receptor and MHC Class-I with that for the Class-I homologous molecule FcRn complexed with the Fc domains of immunoglobulin. It will be seen that a different part of both molecules is involved in the interface seen in these two complexes.
A static view of the above model comparing a space filling model with a protein back-bone view is available.
For more information see D.N.Garboczi, P.Ghosh, U.Utz, Q.R.Fan, W.E.Biddison, D.C.Wiley. Structure of the complex between human T-cell receptor, viral peptide and HLA-A2 Nature 384, 134 (1996)
Mike Clark.