1bxb

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spinqualitylabelsall models 1bxb, resolution 2.2Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

XYLOSE ISOMERASE FROM THERMUS THERMOPHILUS

Overview

The crystal structures of highly thermostable xylose isomerases from, Thermus thermophilus (TthXI) and Thermus caldophilus (TcaXI), both with, the optimum reaction temperature of 90 degrees C, have been determined by, X-ray crystallography. The model of TcaXI has been refined to an R-factor, of 17.8 % for data extending to 2.3 A and that of TthXI to 17.1 % for data, extending to 2.2 A. The tetrameric arrangement of subunits characterized, by the 222-symmetry and the tertiary fold of each subunit in both TcaXI, and TthXI are basically the same as in other xylose isomerases. Each, monomer is composed of two domains. Domain I (residues 1 to 321) folds, into the (beta/alpha)8-barrel. Domain II (residues 322 to 387), lacking, beta-strands, makes extensive contacts with domain I of an adjacent, subunit. Each monomer of TcaXI contains ten beta-strands, 15, alpha-helices, and six 310-helices, while that of TthXI contains ten, beta-strands, 16 alpha-helices, and five 310-helices. Although the, electron density does not indicate the presence of bound metal ions in the, present models of both TcaXI and TthXI, the active site residues show the, conserved structural features. In order to understand the structural basis, for thermostability of these enzymes, their structures have been compared, with less thermostable XIs from Arthrobacter B3728 and Actinoplanes, missouriensis (AXI and AmiXI), with the optimum reaction temperatures of, 80 degrees C and 75 degrees C, respectively. Analyses of various factors, that may affect protein thermostability indicate that the possible, structural determinants of the enhanced thermostability of TcaXI/TthXI, over AXI/AmiXI are (i) an increase in ion pairs and ion-pair networks, (ii) a decrease in the large inter-subunit cavities, (iii) a removal of, potential deamidation/isoaspartate formation sites, and (iv) a shortened, loop.

About this Structure

1BXB is a Single protein structure of sequence from Thermus thermophilus. Active as Xylose isomerase, with EC number 5.3.1.5 Full crystallographic information is available from OCA.

Reference

Crystal structures of thermostable xylose isomerases from Thermus caldophilus and Thermus thermophilus: possible structural determinants of thermostability., Chang C, Park BC, Lee DS, Suh SW, J Mol Biol. 1999 May 14;288(4):623-34. PMID:10329168

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