1x39
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(New page: 200px<br /><applet load="1x39" size="450" color="white" frame="true" align="right" spinBox="true" caption="1x39, resolution 1.80Å" /> '''Crystal structure of...)
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Revision as of 23:16, 24 November 2007
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Crystal structure of barley beta-D-glucan glucohydrolase isoenzyme exo1 in complex with gluco-phenylimidazole
Overview
The interactions of a transition state mimic anilinomethyl glucoimidazole, (AmGlcIm), with a K(i) constant of 0.6 x 10(-)(9) M and a Gibbs free, energy value of -53.5 kJ/mol, with a family GH3 beta-d-glucan, glucohydrolase from barley have been analyzed crystallographically and by, ab initio quantum mechanical modeling. AmGlcIm binds 3 times more tightly, to the beta-d-glucan glucohydrolase than a previously investigated phenyl, glucoimidazole. In the enzyme-AmGlcIm complex, an additional residue, Tyr253, and a water molecule positioned between subsites -1 and +1 are, recruited for binding. Analyses of the two binary complexes reveal the, following. (i) An intricate network exists in which hydrogen bonds between, the enzyme's catalytic pocket residues Lys206, His207, Tyr253, Asp285, and, Glu491 and the glucoimidazoles are shorter by 0.15-0.53 A, compared with, distances of hydrogen bonds in the Michaelis complex. (ii) The "glucose", moiety of the glucoimidazoles adopts a (4)E conformation that is vital for, the low-nanomolar binding. (iii) The N1 atoms of the glucoimidazoles are, positioned nearly optimally for in-line protonation by the Oepsilon1 atom, of the catalytic acid/base Glu491. (iv) The enzyme derives binding, energies from both glycone and aglycone components of the glucoimidazoles., (iv) The prevalent libration motion of the two domains of the enzyme could, play a significant role during induced fit closure in the active site. (v), Modeling based on the structural data predicts that protons could be, positioned on the N1 atoms of the glucoimidazoles, and the catalytic, acid/base Glu491 could carry an overall negative charge. (vi) The, enzyme-AmGlcIm complex reveals the likely structure of an early transition, state during hydrolysis. Finally, the high-resolution structures enabled, us to define minimal structures of oligosaccharides attached to Asn221, Asn498, and Asn600 N-glycosylation sites.
About this Structure
1X39 is a Single protein structure of sequence from Hordeum vulgare with SO4, IDE and GOL as ligands. Active as Glucan 1,3-beta-glucosidase, with EC number 3.2.1.58 Full crystallographic information is available from OCA.
Reference
Structural rationale for low-nanomolar binding of transition state mimics to a family GH3 beta-D-glucan glucohydrolase from barley., Hrmova M, Streltsov VA, Smith BJ, Vasella A, Varghese JN, Fincher GB, Biochemistry. 2005 Dec 20;44(50):16529-39. PMID:16342944
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