Purification, crystallization, and preliminary x-ray studies of a bifunctional 5,10-methenyl/methylene-tetrahydrofolate cyclohydrolase/dehydrogenase from Escherichia coli.

A bifunctional enzyme that catalyzes the conversion of formyltetrahydrofolate to methylene-tetrahydrofolate (5,10-methenyltetrahydrofolate cyclohydrolase and 5,10-methylene tetrahydrofolate dehydrogenase), has been subcloned from a cDNA library, purified to homogeneity, and crystallized. The crystals belong to space group I222, with unit cell dimensions of a = 64.5 A, b = 84.9 A, c = 146.1 A. The crystal unit cell and diffraction is consistent with an asymmetric unit consisting of the enzyme monomer, and a specific volume of the unit cell of 3.2 A3/Da. The crystals diffract to at least 2.8 A resolution after flash-cooling, when using a rotating anode x-ray source and an RAXIS image plate detector. A 2.56 A resolution native data set has been collected at beamline X12-C at the NSLS.