Steve Ealick's Research Group
Thymidine Phosphorylase from E. coli
*1TPT (native tetragonal form)
#2TPT (tetragonal form with no substrates present)
#1OTP (orthorhombic form)
#1AZY (monoclinic form)
Thymidine phosphorylase (TP) catalyzes the reversible phosphorylsis of thymidine and other pyrimidine 2′-deoxyribosides, except for 4-amino substituted compounds. In 1990, we reported the three-dimensional structure of thymidine phosphorylase from Escherichia coli at 2.8 Å resolution using multiple-isomorphous-replacement techniques. In 1998, we determined the crystal structure at higher resolution and identified two additional crystal forms.
Each subunit of thymidine phosphorylase is composed of a small α-helical domain of six helices and a large α/βdomain. The α/βdomain includes a six-stranded mixed β-sheet and a four-stranded antiparallel β-sheet. The active site lies in a cavity between the small and large domains. The central β-sheet is splayed open to accomodate a putative phosphate-binding site which is probably occupied by a sulfate ion in the crystal. This image is of the tetragonal crystal form with sulfate shown in the active site.
Thymidine phosphorylase exists in a tetragonal (space group P43212) crystal form as an S-shaped dimer in which the subunits are related by a crystallographic 2-fold axis.
Schematic diagrams show the residues at the phosphate binding site and at the pyrimidine binding site.
#Pugmire MJ, Cook WJ, Jasanoff A, Walte, MR, and Ealick SE. Structural and Theoretical Studies Suggest Domain Movement Produces an Active Conformation of Thymidine Phosphorylase. J. Molec. Biol. 281:285-299 (1998).
*Walter MR, Cook WJ, Cole LB, Short SA, Koszalka GW, Krenitsky TA, and Ealick SE. Three-Dimensional Structure of Thymidine Phosphorylase from Escherichia coli at 2.8Å Resolution J. Biol. Chem. 265(23):14016-14022 (1990).
Cook WJ, Koszalka GW, Hall WW, Burns CL, and Ealick SE. Crystallization and Preliminary X-ray Investigation of Thymidine Phosphorylase from Escherichia coli. J. Biol. Chem. 262(8):3788-3789 (1987).