We next tested whether gross misfolding was the reason for the inability of some of the mutants to precipitate hTfR1 and to bind to the cell-surface of MACV-permissive Vero cells. We performed far-UV circular dichroism (CD) of the wt GP1D and selected mutants (Fig. 2D ). Far-UV CD spectra were taken in PBS at 5uC with a Jasco-810 spectropolarimeter and a 1 mm pathlength rectangular quartz cell. Protein solutions used were from 0.05 to 0.08 mg/ml. Ten scans were accumulated and averaged, without smoothing. The spectra all revealed a single broad minimum in the range of 108 to 216 nm. These results are consistent with similar folding of the wt and mutant proteins, although small changes in the conformation of the mutants cannot be ruled out (the Fc portion of the protein as well as GP1D contributed to the measured signal).