TCRs Interact Differently with Class I and Class II Molecules

Can the conclusions drawn from the three-dimensional structure of TCR-peptide-class I complexes be extrapolated to interactions of TCR with class II complexes? Ellis Reinherz and his colleagues resolved this question by analysis of a TCR molecule in complex with a mouse class II molecule and its specific antigen. While the structures of the peptide-binding regions in class I and class II molecules are similar, Chapter 7 showed that there are differences in how they accommodate bound peptide (see Figures 7-10a and b). A comparison of the interactions of a TCR with class I MHC-peptide and class II-peptide reveals a significant difference in the angle at which the TCR molecule sits on the MHC complexes (Figure 9-14). Also notable is a greater number of contact residues between TCR and class II MHC, which is consistent with the known higher affinity of interaction. However, it remains to be seen whether the evident difference in the number of contact points will be true for all class I and II structures.

Tcr Peptide Class Mhc

FIGURE 9-14

(a) TCR-peptide-class I MHC (b) TCR-peptide-class II MHC

FIGURE 9-14

(a) TCR-peptide-class I MHC (b) TCR-peptide-class II MHC

Comparison of the interactions between ap TCR and (a) class I MHC-peptide, and (b) class II MHC-peptide. The TCR (wire diagram) is red in (a), blue-green in (b); the MHC molecules are shown as surface models; peptide is shown as ball and stick. [From Reinherz et al., 1999, Science 286:1913.]

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Essentials of Human Physiology

Essentials of Human Physiology

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