Crystallization of recombinant Leishmania major pteridine reductase 1 (PTR1)

The enzyme pteridine reductase (PTR1) has recently been discovered in the p rotozoan parasite Leishmania and validated as a target for therapeutic inte rvention. PTR1 is responsible for the salvage of pteridines and also contri butes to antifolate drug resistance. Structural analysis, in combination wi th ongoing biochemical characterization will assist the elucidation of the structure-activity relationships of this important enzyme and support a str ucture-based approach to discover novel inhibitors. Recombinant L. major PT R1 has been purified from an Escherichia coli expression system and used in crystallization experiments. Orthorhombic crystals have been obtained and data to 2.8 Angstrom has been measured. The space group is P2(1)2(1)2 or P2 (1)2(1)2(1) with unit-cell dimensions of a = 103.9, b = 134.7, c = 96.2 Ang strom. One homotetramer, of molecular mass approximately 120 kDa, probably constitutes the asymmetric unit and gives a Matthews coefficient, V-m, of 2 .8 Angstrom(3) Da(-1) and 56% solvent volume. Self-rotation function calcul ations show a single well defined noncrystallographic twofold axis with fea tures that might represent additional elements of non-crystallographic symm etry. The detail of exactly what constitutes the asymmetric unit will be re solved by structure determination.