National Center for
3OF6: Human Pre-T Cell Receptor Crystal Structure
Nature (2010) 467 p.844-848
The pre-T-cell antigen receptor (pre-TCR), expressed by immature thymocytes, has a pivotal role in early T-cell development, including TCR beta-selection, survival and proliferation of CD4(-)CD8(-) double-negative thymocytes, and subsequent alphabeta T-cell lineage differentiation. Whereas alphabetaTCR ligation by the peptide-loaded major histocompatibility complex initiates T-cell signalling, pre-TCR-induced signalling occurs by means of a ligand-independent dimerization event. The pre-TCR comprises an invariant alpha-chain (pre-Talpha) that pairs with any TCR beta-chain (TCRbeta) following successful TCR beta-gene rearrangement. Here we provide the basis of pre-Talpha-TCRbeta assembly and pre-TCR dimerization. The pre-Talpha chain comprised a single immunoglobulin-like domain that is structurally distinct from the constant (C) domain of the TCR alpha-chain; nevertheless, the mode of association between pre-Talpha and TCRbeta mirrored that mediated by the Calpha-Cbeta domains of the alphabetaTCR. The pre-TCR had a propensity to dimerize in solution, and the molecular envelope of the pre-TCR dimer correlated well with the observed head-to-tail pre-TCR dimer. This mode of pre-TCR dimerization enabled the pre-Talpha domain to interact with the variable (V) beta domain through residues that are highly conserved across the Vbeta and joining (J) beta gene families, thus mimicking the interactions at the core of the alphabetaTCR's Valpha-Vbeta interface. Disruption of this pre-Talpha-Vbeta dimer interface abrogated pre-TCR dimerization in solution and impaired pre-TCR expression on the cell surface. Accordingly, we provide a mechanism of pre-TCR self-association that allows the pre-Talpha chain to simultaneously 'sample' the correct folding of both the V and C domains of any TCR beta-chain, regardless of its ultimate specificity, which represents a critical checkpoint in T-cell development. This unusual dual-chaperone-like sensing function of pre-Talpha represents a unique mechanism in nature whereby developmental quality control regulates the expression and signalling of an integral membrane receptor complex.