1ijh
From Proteopedia
(New page: 200px<br /><applet load="1ijh" size="450" color="white" frame="true" align="right" spinBox="true" caption="1ijh, resolution 1.53Å" /> '''CHOLESTEROL OXIDASE ...) |
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| - | [[Image:1ijh.gif|left|200px]]<br /><applet load="1ijh" size=" | + | [[Image:1ijh.gif|left|200px]]<br /><applet load="1ijh" size="350" color="white" frame="true" align="right" spinBox="true" |
caption="1ijh, resolution 1.53Å" /> | caption="1ijh, resolution 1.53Å" /> | ||
'''CHOLESTEROL OXIDASE FROM STREPTOMYCES ASN485LEU MUTANT'''<br /> | '''CHOLESTEROL OXIDASE FROM STREPTOMYCES ASN485LEU MUTANT'''<br /> | ||
==Overview== | ==Overview== | ||
| - | Cholesterol oxidase catalyzes the oxidation and isomerization of | + | Cholesterol oxidase catalyzes the oxidation and isomerization of cholesterol to cholest-4-en-3-one. An asparagine residue (Asn485) at the active site is believed to play an important role in catalysis. To test the precise role of Asn485, we mutated it to a leucine and carried out kinetic and crystallographic studies. Steady-state kinetic analysis revealed a 1300-fold decrease in the oxidation k(cat)/K(m) for the mutant enzyme whereas the k(cat)/K(m) for isomerization is only 60-fold slower. The primary kinetic isotope effect in the mutant-catalyzed reaction indicates that 3alpha-H transfer remains the rate-determining step. Measurement of the reduction potentials for the wild-type and N485L enzymes reveals a 76 mV decrease in the reduction potential of the FAD for the mutant enzyme relative to wild type. The crystal structure of the mutant, determined to 1.5 A resolution, reveals a repositioning of the side chain of Met122 near Leu485 to form a hydrophobic pocket. Furthermore, the movement of Met122 facilitates the binding of an additional water molecule, possibly mimicking the position of the equatorial hydroxyl group of the steroid substrate. The wild-type enzyme shows a novel N-H...pi interaction between the side chain of Asn485 and the pyrimidine ring of the cofactor. The loss of this interaction in the N485L mutant destabilizes the reduced flavin and accounts for the decreased reduction potential and rate of oxidation. Thus, the observed structural rearrangement of residues at the active site, as well as the kinetic data and thermodynamic data for the mutant, suggests that Asn485 is important for creating an electrostatic potential around the FAD cofactor enhancing the oxidation reaction. |
==About this Structure== | ==About this Structure== | ||
| - | 1IJH is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Streptomyces_sp. Streptomyces sp.] with FAD as [http://en.wikipedia.org/wiki/ligand ligand]. Active as [http://en.wikipedia.org/wiki/Cholesterol_oxidase Cholesterol oxidase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=1.1.3.6 1.1.3.6] Full crystallographic information is available from [http:// | + | 1IJH is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Streptomyces_sp. Streptomyces sp.] with <scene name='pdbligand=FAD:'>FAD</scene> as [http://en.wikipedia.org/wiki/ligand ligand]. Active as [http://en.wikipedia.org/wiki/Cholesterol_oxidase Cholesterol oxidase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=1.1.3.6 1.1.3.6] Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1IJH OCA]. |
==Reference== | ==Reference== | ||
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[[Category: Single protein]] | [[Category: Single protein]] | ||
[[Category: Streptomyces sp.]] | [[Category: Streptomyces sp.]] | ||
| - | [[Category: Lario, P | + | [[Category: Lario, P I.]] |
[[Category: Vrielink, A.]] | [[Category: Vrielink, A.]] | ||
[[Category: FAD]] | [[Category: FAD]] | ||
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[[Category: steroid metabolism]] | [[Category: steroid metabolism]] | ||
| - | ''Page seeded by [http:// | + | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Feb 21 13:12:28 2008'' |
Revision as of 11:12, 21 February 2008
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CHOLESTEROL OXIDASE FROM STREPTOMYCES ASN485LEU MUTANT
Overview
Cholesterol oxidase catalyzes the oxidation and isomerization of cholesterol to cholest-4-en-3-one. An asparagine residue (Asn485) at the active site is believed to play an important role in catalysis. To test the precise role of Asn485, we mutated it to a leucine and carried out kinetic and crystallographic studies. Steady-state kinetic analysis revealed a 1300-fold decrease in the oxidation k(cat)/K(m) for the mutant enzyme whereas the k(cat)/K(m) for isomerization is only 60-fold slower. The primary kinetic isotope effect in the mutant-catalyzed reaction indicates that 3alpha-H transfer remains the rate-determining step. Measurement of the reduction potentials for the wild-type and N485L enzymes reveals a 76 mV decrease in the reduction potential of the FAD for the mutant enzyme relative to wild type. The crystal structure of the mutant, determined to 1.5 A resolution, reveals a repositioning of the side chain of Met122 near Leu485 to form a hydrophobic pocket. Furthermore, the movement of Met122 facilitates the binding of an additional water molecule, possibly mimicking the position of the equatorial hydroxyl group of the steroid substrate. The wild-type enzyme shows a novel N-H...pi interaction between the side chain of Asn485 and the pyrimidine ring of the cofactor. The loss of this interaction in the N485L mutant destabilizes the reduced flavin and accounts for the decreased reduction potential and rate of oxidation. Thus, the observed structural rearrangement of residues at the active site, as well as the kinetic data and thermodynamic data for the mutant, suggests that Asn485 is important for creating an electrostatic potential around the FAD cofactor enhancing the oxidation reaction.
About this Structure
1IJH is a Single protein structure of sequence from Streptomyces sp. with as ligand. Active as Cholesterol oxidase, with EC number 1.1.3.6 Full crystallographic information is available from OCA.
Reference
The presence of a hydrogen bond between asparagine 485 and the pi system of FAD modulates the redox potential in the reaction catalyzed by cholesterol oxidase., Yin Y, Sampson NS, Vrielink A, Lario PI, Biochemistry. 2001 Nov 20;40(46):13779-87. PMID:11705367
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