1i1x
From Proteopedia
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1.11 A ATOMIC RESOLUTION STRUCTURE OF A THERMOSTABLE XYLANASE FROM THERMOASCUS AURANTIACUS
Overview
Thermoascus aurantiacus xylanase is a thermostable enzyme which hydrolyses, xylan, a major hemicellulose component of the biosphere. The crystal, structure of this F/10 family xylanase, which has a triosephosphate, isomerase (TIM) barrel (beta/alpha)(8) fold, has been solved to, small-molecule accuracy at atomic resolution (1.11 A) at 293 K (RTUX) and, at ultrahigh resolution (0.89 A) at 100 K (CTUX) using X-ray diffraction, data sets collected on a synchrotron light source, resulting in R/R(free), values of 9.94/12.36 and 9.00/10.61% (for all data), respectively. Both, structures were refined with anisotropic atomic displacement parameters., The 0.89 A structure, with 177 476 observed unique reflections, was, refined without any stereochemical restraints during the final stages. The, salt bridge between Arg124 and Glu232, which is bidentate in RTUX, is, water-mediated in CTUX, suggesting the possibility of plasticity of ion, pairs in proteins, with water molecules mediating some of the alternate, arrangements. Two buried waters present inside the barrel form, hydrogen-bond interactions with residues in strands beta2, beta3, beta4, and beta7 and presumably contribute to structural stability. The, availability of accurate structural information at two different, temperatures enabled the study of the temperature-dependent deformations, of the TIM-barrel fold of the xylanase. Analysis of the deviation of, corresponding C(alpha) atoms between RTUX and CTUX suggests that the, interior beta-strands are less susceptible to changes as a function of, temperature than are the alpha-helices, which are on the outside of the, barrel. betaalpha-loops, which are longer and contribute residues to the, active-site region, are more flexible than alphabeta-loops. The 0.89 A, structure represents one of the highest resolution structures of a protein, of such size with one monomer molecule in the asymmetric unit and also, represents the highest resolution TIM-barrel fold structure to date. It, may provide a useful template for theoretical modelling studies of the, structure and dynamics of the ubiquitous TIM-barrel fold.
About this Structure
1I1X is a Single protein structure of sequence from Thermoascus aurantiacus. Active as Endo-1,4-beta-xylanase, with EC number 3.2.1.8 Full crystallographic information is available from OCA.
Reference
Thermostable xylanase from Thermoascus aurantiacus at ultrahigh resolution (0.89 A) at 100 K and atomic resolution (1.11 A) at 293 K refined anisotropically to small-molecule accuracy., Natesh R, Manikandan K, Bhanumoorthy P, Viswamitra MA, Ramakumar S, Acta Crystallogr D Biol Crystallogr. 2003 Jan;59(Pt 1):105-17. Epub 2002, Dec 19. PMID:12499546
Page seeded by OCA on Tue Nov 20 16:59:01 2007
