Preliminary joint X-ray and neutron protein crystallographic studies of ecDHFR complexed with folate and NADP\u3csup\u3e+\u3c/sup\u3e

A crystal of Escherichia coli dihydrofolate reductase (ecDHFR) complexed with folate and NADP+ of 4 x 1.3 x 0.7 mm (3.6 mm3) in size was obtained by sequential application of microseeding and macroseeding. A neutron diffraction data set was collected to 2.0 A resolution using the IMAGINE diffractometer at the High Flux Isotope Reactor within Oak Ridge National Laboratory. A 1.6 A resolution X-ray data set was also collected from a smaller crystal at room temperature. The neutron and X-ray data were used together for joint refinement of the ecDHFR–folate–NADP+ ternary-complex structure in order to examine the protonation state, protein dynamics and solvent structure of the complex, furthering understanding of the catalytic mechanism