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Structure of the tetrameric form of human L‐Xylulose reductase: Probing the inhibitor‐binding site with molecular modeling and site‐directed mutagenesis
Author(s) -
ElKabbani Ossama,
Carbone Vincenzo,
Darmanin Connie,
Ishikura Syuhei,
Hara Akira
Publication year - 2005
Publication title -
proteins: structure, function, and bioinformatics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.699
H-Index - 191
eISSN - 1097-0134
pISSN - 0887-3585
DOI - 10.1002/prot.20487
Subject(s) - tetramer , stereochemistry , active site , chemistry , salt bridge , mutagenesis , binding site , protein quaternary structure , biochemistry , reductase , molecular model , structural motif , site directed mutagenesis , protein subunit , enzyme , protein structure , mutant , gene
L‐Xylulose reductase (XR) is a member of the short‐chain dehydrogenase/reductase (SDR) superfamily. In this study we report the structure of the biological tetramer of human XR in complex with NADP + and a competitive inhibitor solved at 2.3 Å resolution. A single subunit of human XR is formed by a centrally positioned, seven‐stranded, parallel β‐sheet surrounded on either side by two arrays of three α‐helices. Two helices located away from the main body of the protein form the variable substrate‐binding cleft, while the dinucleotide coenzyme‐binding motif is formed by a classical Rossmann fold. The tetrameric structure of XR, which is held together via salt bridges formed by the guanidino group of Arg203 from one monomer and the carboxylate group of the C‐terminal residue Cys244 from the neighboring monomer, explains the ability of human XR to prevent the cold inactivation seen in the rodent forms of the enzyme. The orientations of Arg203 and Cys244 are maintained by a network of hydrogen bonds and main‐chain interactions of Gln137, Glu238, Phe241, and Trp242. These interactions are similar to those defining the quaternary structure of the closely related carbonyl reductase from mouse lung. Molecular modeling and site‐directed mutagenesis identified the active site residues His146 and Trp191 as forming essential contacts with inhibitors of XR. These results could provide a structural basis in the design of potent and specific inhibitors for human XR. Proteins 2005. © 2005 Wiley‐Liss, Inc.