THE STRUCTURE OF THE DETOXIFICATION ENZYME: GLUTATHIONE S-TRANSFERASE D21 FROM DROSOPHILA MELANOGASTER. Ping-lin Ong^1,2, John P. Rose², C.-P. D. Tu³ and B.C. Wang². ¹Dept. of Biological Sciences, Univ. of Pittsburgh, Pittsburgh, PA 15260, U.S.A., ²Dept. of Biochemistry and Molecular Biology, Univ. of Georgia, Athens, GA 30602, U.S.A. and ³Dept. of Biochemistry and Molecular Biology, Pennsylvania State Univ., College Park, PA 16802, U.S.A.

The crystal structure of Drosophila melanogaster Glutathione S-transferase D21 (GST-D21) has been determined at 2.5Å resolution by molecular replacement.

Glutathione S-transferases (GSTs) (EC 2.5.1.18) are a family of multi-functional enzymes involved in the cellular detoxification and excretion of many physiological and xenobiotic substances. Five GST classes: mu, pi, alpha, theta, and microsomal have been reported.

GST-D21 is a member of the theta class GSTs. It was crystallized from PEG4000, pH 7.5 . A data set to 2.5Å resolution was collected on a Siemens X-100 area detector. The data were indexed integrated and scaled using XENGEN 2.1 and gave an Rsym of 5.3%. The crystal indexed in a primitive monoclinic lattice with cell constants a=53.76Å, b=89.70Å, c=50.89Å, [[beta]]=113.75deg.. The are two GST-D21 molecules in the asymmetric unit and the Matthews coefficient is calculated to be 2.33. Analysis of the systematic absences uniquely determined the P2₁ space group.

The structure was solved by molecular replacement (AMoRe) using blow fly GST (Wilce, et al., 1995)as a search model. The initial model was rebuilt by fitting correct sequence into the 2Fo-Fc electron density map. The structure was refined against 8-2.5Å data using X-PLOR 3.1. Non-crystallographic symmetry constraints were imposed throughout the refinement.

The structure at the current stage of refinement, 3476 non-hydrogen atoms, no solvent molecules are included,has an R value of 22% and an Rfree value of 29%. A structural comparison of the different GST classes and a structural explanation of GST function will be described in detail.

This research was supported by NIH grant GM 49205.