Comparison of the Fab-EPOR complex with the EPO-activated EPOR crystal structure. Two copies of ABT007 Fab (blue) complexed to EPO-activated EPOR dimer (green) are superimposed onto the EPO-activated (red) EPOR dimer (brown, 1EER)⁷  complex. Two independent Fab fragments can be accommodated on the EPO-activated form of EPOR, but the carboxyl termini of the Fab fragments are too distant (11.3 nm) to be derived from a single IgG.