T cell receptor-MHC interactions up close

X-ray crystal structures of αβTCRs bound to MHCI and MHCII molecules with bound antigenic peptides reveals the atomic contacts upon which MHC restricted T cell recognition is based. Very different signals can result from very similar structures and identical signals can result from different structures (Figures 2C and 2D). An important caveat is that the CD3 and zeta chains of the TCRs and all of the transmembrane anchors and cytoplasmic segments were absent from all of the crystal studied to date. The possibility, for example, that the cell surface TCR contain two αβTCR units (Fernandez-Miguel et al., 1999) suggest that until the full TCR with CD3 and zeta chains is assembled and crystallized, choosing among signal initiation mechanism involving oligomerization or allosteric switches will be difficult.