CLONING, EXPRESSION, AND CRYSTALLIZATION OF THE V-DELTA DOMAIN OF A HUMAN GAMMA-DELTA T-CELL RECEPTOR

T-lymphocytes recognize a wide variety of antigens through highly dive rse cell-surface glycoproteins known as T-cell receptors (TCRs). These disulfide-linked heterodimers are composed of alpha and beta or gamma and delta polypeptide chains consisting of variable (V) and constant (C) domains non-covalently associated with at least four invariant cha ins to form the TCR-CD3 complex. It is well established that alpha bet a 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 alpha beta TCRs has recently bec ome available through X-ray crystallography. In contrast, the antigen specificity of gamma delta TCRs is much less well understood and their three-dimensional structure is unknown. We have cloned the delta chai n of a human TCR specific for the MHC class I HLA-A2 molecule and expr essed the V domain as a secreted protein in the periplasmic space of E scherichia coli. Following affinity purification using a nickel chelat e adsorbent, the recombinant V delta domain was crystallized in a form suitable for X-ray diffraction analysis. The crystals are orthorhombi c, space group P2(1)2(1)2 with unit cell dimensions a = 69.9, b = 49.0 , c = 61.6 Angstrom, and diffract to beyond 2.3 Angstrom resolution. T he ability of a V delta domain produced in bacteria to form well-order ed crystals strongly suggests that the periplasmic space can provide a suitable environment for the correct in vivo folding of gamma delta T CRs.