1xym: Difference between revisions

Revision as of 15:40, 3 May 2008

THE ROLE OF THE DIVALENT METAL ION IN SUGAR BINDING, RING OPENING, AND ISOMERIZATION BY D-XYLOSE ISOMERASE: REPLACEMENT OF A CATALYTIC METAL BY AN AMINO-ACID

OverviewOverview

The distinct roles of the two magnesium ions essential to the activity of D-xylose isomerase from Streptomyces olivochromogenes were examined. The enzyme-magnesium complex was isolated, and the stoichiometry of cation binding determined by neutron activation analysis to be 2 mol of magnesium per mole of enzyme. A plot of Mg2+ added versus Mg2+ bound to enzyme is consistent with apparent KD values of < or = 0.5-1.0 mM for one Mg2+ and < or = 2-5 mM for the second. A site-directed mutant of D-xylose isomerase was designed to remove the tighter, tetracoordinated magnesium binding site (site 1, Mg-1); Glu180 was replaced with Lys180. The stoichiometry of metal binding to this mutant, E180K, is 1 mol of magnesium per mole of enzyme. Ring-opening assays with 1-thioglucose (H2S released upon ring opening) show E180K catalyzes the opening of the sugar ring at 20% the rate of the wild-type, but E180K does not catalyze isomerization of glucose to fructose. Thus, the magnesium bound to Glu180 is essential for isomerization but not essential for ring opening. The X-ray crystallographic structures of E180K in the absence of magnesium and in the presence and absence of 250 mM glucose were obtained to 1.8-A resolution and refined to R factors of 17.7% and 19.7%, respectively. The wild-type and both E180K structures show no significant structural differences, except the epsilon-amino group of Lys180, which occupies the position usually occupied by the Mg-1.(ABSTRACT TRUNCATED AT 250 WORDS)

About this StructureAbout this Structure

1XYM is a Single protein structure of sequence from Streptomyces olivochromogenes. Full crystallographic information is available from OCA.

ReferenceReference

Role of the divalent metal ion in sugar binding, ring opening, and isomerization by D-xylose isomerase: replacement of a catalytic metal by an amino acid., Allen KN, Lavie A, Glasfeld A, Tanada TN, Gerrity DP, Carlson SC, Farber GK, Petsko GA, Ringe D, Biochemistry. 1994 Feb 15;33(6):1488-94. PMID:7906142 Page seeded by OCA on Sat May 3 15:40:13 2008

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OCA

@@ Line 1: / Line 1: @@
 [[Image:1xym.gif|left|200px]]
- {{Structure
+<!--
-|PDB= 1xym |SIZE=350|CAPTION= <scene name='initialview01'>1xym</scene>, resolution 1.8&Aring;
+The line below this paragraph, containing "STRUCTURE_1xym", creates the "Structure Box" on the page.
-|SITE=
+You may change the PDB parameter (which sets the PDB file loaded into the applet)
-|LIGAND= <scene name='pdbligand=GLO:D-GLUCOSE+IN+LINEAR+FORM'>GLO</scene>, <scene name='pdbligand=MG:MAGNESIUM+ION'>MG</scene>, <scene name='pdbligand=OH:HYDROXIDE+ION'>OH</scene>
+or the SCENE parameter (which sets the initial scene displayed when the page is loaded),
-|ACTIVITY= <span class='plainlinks'>[http://en.wikipedia.org/wiki/Xylose_isomerase Xylose isomerase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=5.3.1.5 5.3.1.5] </span>
+or leave the SCENE parameter empty for the default display.
-|GENE=
+-->
-|DOMAIN=
+{{STRUCTURE_1xym|  PDB=1xym  |  SCENE=  }}
-|RELATEDENTRY=
-|RESOURCES=<span class='plainlinks'>[http://oca.weizmann.ac.il/oca-docs/fgij/fg.htm?mol=1xym FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=1xym OCA], [http://www.ebi.ac.uk/pdbsum/1xym PDBsum], [http://www.rcsb.org/pdb/explore.do?structureId=1xym RCSB]</span>
-}}
 '''THE ROLE OF THE DIVALENT METAL ION IN SUGAR BINDING, RING OPENING, AND ISOMERIZATION BY D-XYLOSE ISOMERASE: REPLACEMENT OF A CATALYTIC METAL BY AN AMINO-ACID'''
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 [[Category: Petsko, G A.]]
 [[Category: Ringe, D.]]
-[[Category: isomerase(intramolecular oxidoreductase)]]
+''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sat May  3 15:40:13 2008''
-''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Mar 31 00:56:24 2008''