Cloning, expression, and crystallization of the Vδ domain of a human γδ T-cell receptor

T-lymphocytes recognize a wide variety of antigens through highly diverse cell-surface glycoproteins known as T-cell receptors (TCRs). These disulfide-linked heterodimers are composed of α and β or γ and δ polypeptide chains consisting of variable (V) and constant (C) domains non-covalently associated with at least four invariant chains to form the TCR-CD3 complex. It is well established that αβ TCRs recognize antigen in the form of peptides bound to molecules of the major histocompatibility complex (MHC); furthermore, information on the three-dimensional structure of αβ TCRs has recently become available through X-ray crystallography. In contrast, the antigen specificity of γδ TCRs is much less well understood and their three-dimensional structure is unknown. We have cloned the δ chain of a human TCR specific for the MHC class I HLA-A2 molecule and expressed the V domain as a secreted protein in the periplasmic space of Escherichia coli. Following affinity purification using a nickel chelate adsorbent, the recombinant Vδ domain was crystallized in a form suitable for X-ray diffraction analysis. The crystals are orthorhombic, space group P2₁2₁2 with unit cell dimensions a = 69.9, b = 49.0, c = 61.6 Å, and diffract to beyond 2.3 Å resolution. The ability of a Vδ domain produced in bacteria to form well-ordered crystals strongly suggests that the periplasmic space can provide a suitable environment for the correct in vivo folding of γδ TCRs.