Crystallization and preliminary X-ray analysis of the formiminotransferase domain from the bifunctional enzyme formiminotransferase-cyclodeaminase

Formiminotransferase-cyclodeaminase (E.C. 2.1.2.5-E.C. 4.3.1.4) is a bifunctional enzyme involved in the histidine-degradation pathway which exhibits specificity for polyglutamylated folate substrates. The first function of the enzyme transfers the formimino group of formiminoglutamate to the N⁵ position of tetrahydrofolate, while the second function catalyses the cyclodeamination of the formimino group, yielding N^5,10-methenyl-tetrahydrofolate, with efficient channeling of the intermediate between these activities. Initial studies have shown that the enzyme consists of eight identical subunits of 62 kDa each, arranged as a circular tetramer of dimers. It is this formation which results in two different dimeric interfaces, which are necessary for the two different activities. The identical subunits have been shown to consist of two domains, each of which can be obtained as dimers. The formiminotransferase domain has been crystallized in the presence of the substrate analogue folinic acid. The crystals belong to space group P2₁2₁2₁, with unit-cell dimensions a = 64.4, b = 103.7, c = 122.3 Å. Both a native data set and a mercurial derivative data set have been collected to 2.8 Å resolution.