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

Formiminotransferase-cyclodeaminase (E.C. 2.1.2.5-E.C. 4.3.1.4) is a bifunc tional enzyme involved in the histidine-degradation pathway which exhibits specificity for polyglutamylated folate substrates. The first function of t he enzyme transfers the formimino group of formiminoglutamate to the N-5 po sition of tetrahydrofolate, while the second function catalyses the cyclode amination of the formimino group yielding N-5,N-10-methenyl-tetrahydrofolat e, with efficient channeling of the intermediate between these activities. Initial studies have shown that the enzyme consists of eight identical subu nits of 62 kDa each, arranged as a circular tetramer of dimers. It is this formation which results in two different dimeric interfaces, which are nece ssary for the two different activities. The identical subunits have been sh own to consist of two domains, each of which can be obtained as dimers. The formiminotransferase domain has been crystallized in the presence of the s ubstrate analogue folinic acid. The crystals belong to space group P2(1)2(1 )2(1), With unit-cell dimensions a = 64.4, b = 103.7, c = 122.3 Angstrom. B oth a native data set and a mercurial derivative data set have been collect ed to 2.8 Angstrom resolution.