Crystallization and preliminary X-ray diffraction analysis of the complex of a human anti-ephrin type-A receptor 2 antibody fragment and its cognate antigen.

The recombinant N-terminal domain of human ephrin type-A receptor 2 (rEphA2) has been crystallized in complex with the recombinantly produced Fab fragment of a fully human antibody (1C1; IgG1/kappa). These are the first reported crystals of an ephrin receptor bound to an antibody. The orthorhombic crystals belonged to space group C222(1) (the 00l reflections obey the l = 2n rule), with unit-cell parameters a = 78.93, b = 120.79, c = 286.20 A. The diffraction of the crystals extended to 2.0 A resolution. However, only data to 2.55 A resolution were considered to be useful owing to spot overlap caused by the long unit-cell parameter. The asymmetric unit is most likely to contain two 1C1 Fab-rEphA2 complexes. This corresponds to a crystal volume per protein weight (V(M)) of 2.4 A(3) Da(-1) and a solvent content of 49.5%. The three-dimensional structure of this complex will shed light on the molecular basis of 1C1 specificity. This will also contribute to a better understanding of the mechanism of action of this antibody, the current evaluation of which as an antibody-drug conjugate in cancer therapy makes it a particularly interesting case study.