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Information on aldose reductase is also available at [http://en.wikipedia.org/wiki/Aldose_reductase Wikipedia] | Information on aldose reductase is also available at [http://en.wikipedia.org/wiki/Aldose_reductase Wikipedia] | ||
==Introduction== | ==Introduction== | ||
<scene name='Sandbox_Reserved_339/Default_scene/1'>Aldose reductase</scene> is an | <scene name='Sandbox_Reserved_339/Default_scene/1'>Aldose reductase</scene> is an enzyme that can reduce the aldehyde group of aldoses, aliphatic, aromatic aldehydes and some keto groups from aromatic and aliphatic ketones to their corresponding alcohol products using NADPH as a cofactor.<ref name="Steuber"> PMID 17368668 </ref><ref name="review"> PMID 15094999 </ref> Aldose reductase is most well known in the first step of the polyol pathway of glucose metabolism (Figure 1).<ref name="Steuber"/><ref name="review"/> | ||
[[Image:Polyol_pathway.jpg|left|400px|thumb|Figure 1. Polyol pathway of glucose metabolism. Adapted from Petrash JM. All in the family: aldose reductase and closely related aldo-keto reductases. Cell Mol Life Sci. 2004 Apr;61(7-8):737-49. PMID:15094999 doi:10.1007/s00018-003-3402-3]] | |||
==Polyol Pathway and Diabetes== | |||
As figure 1 shows, the polyol pathway involves the synthesis of fructose from glucose.<ref name="Steuber"/><ref name="review"/> The first step of the pathway is the production of sorbitol from glucose, catalyzed by aldose reductase and using NADPH as a reducing cofactor.<ref name="Steuber"/><ref name="review"/> The second step in the pathway is the production of fructose from sorbitol, catalyzed by sorbitol dehydrogenase using NAD+.<ref name="Steuber"/><ref name="review"/> Under normal blood glucose levels most glucose is metabolized through glycolysis or the pentose phosphate pathway while only a small amount of glucose is metabolized through the polyol pathway.<ref name="review"/> Under the hyperglycemic conditions of diabetes the flux of glucose through the polyol pathway is increased.<ref name="Steuber"/><ref name="review"/> This causes osmotic and oxidative stress, which can cause pathological interferences with cytokine signalling, regulation of apoptosis, and activation of kinase cascades.<ref name="Steuber"/> For example, under increased glucose flux through the polyol pathway protein kinase C activivty increases, which causes smooth muscle cell proliferation of blood vessels in agreement with atherosclerosis.<ref name="Steuber"/> This explains estimates that 75-80% of adults with diabetes die from complications of atherosclerosis.<ref name="Steuber"/> Aldose reductase is also linked to long-term diabetic complications such as retinopathy, nephropathy, neuropathy, cataracts, and angiopathy.<ref name="Steuber"/> Aldose reductase inhibitors are possible beneficial treatment options for diabetes.<ref name="Steuber"/> | |||
==Structure== | ==Structure== | ||
Aldose reductase is a 36kDa aldo-keto reductase made of a single 315 amino acid residue polypeptide chain.<ref name="Steuber"/><ref name="review"/> It has a (β/α)8-<scene name='Sandbox_Reserved_339/Tim_barrel/ | Aldose reductase is a 36kDa aldo-keto reductase made of a single 315 amino acid residue polypeptide chain.<ref name="Steuber"/><ref name="review"/> It has a (β/α)8-<scene name='Sandbox_Reserved_339/Tim_barrel/2'>TIM-barrel</scene> structural motif made of 8 parallel β-strands connected to 8 peripheral α-helices running anti-parallel to the β-strands.<ref name="Steuber"/><ref name="review"/> Including the β-strands and α-helices of the TIM barrel, aldose reductase has a total of 10 <scene name='Sandbox_Reserved_339/Helices_and_strands/1'>α-helices and 13 β-strands</scene>. The catalytic active site is located at the C-terminal loop of the enzyme deeply buried inside the barrel core.<ref name="Steuber"/><ref name="review"/> This site consists of residues that are most likely involved in the catalytic reaction (including residues Tyr48, Lys77, His110).<ref name="Steuber"/> The <scene name='Sandbox_Reserved_339/Nadph/2'>NADPH</scene> cofactor is situated at the top of the barrel with the nicotinamide ring projecting down the center of the barrel and the pyrophosphate straddling the lip of the barrel.<ref name="review"/> Trp111 and the nicotinamide moiety of NADPH interact with the head group of most <scene name='Sandbox_Reserved_339/Ligand/1'>ligands</scene>.<ref name="Steuber"/> Hydrophobic contacts can be formed by the side-chains of Trp20, Val47, Trp79, and Trp219.<ref name="Steuber"/> | ||
===Aldose Reductase Structure and Inhibitors=== | ===Aldose Reductase Structure and Inhibitors=== | ||
Most inhibitors that bind tightly to aldose reductase have a polar group, which is usually a carboxylate, that is attached to a hydrophobic core.<ref name="review"/> Inhibitors bind with their polar head group oriented close to the pyridine ring and usually form hydrogen bonds with Tyr48, His110, and Tyr111.<ref name="review"/> Hydrophobic interactions between the inhibitor and the residues that line the active site help to stabilize the ternary enzyme-coenzyme-inhibitor complex. <ref name="review"/> | Most inhibitors that bind tightly to aldose reductase have a polar group, which is usually a carboxylate, that is attached to a hydrophobic core.<ref name="review"/> Inhibitors bind with their polar head group oriented close to the pyridine ring and usually form hydrogen bonds with Tyr48, His110, and Tyr111.<ref name="review"/> Hydrophobic interactions between the inhibitor and the residues that line the active site help to stabilize the ternary enzyme-coenzyme-inhibitor complex. <ref name="review"/> | ||
==Mechanism== | ==Mechanism== | ||
The exact mechanism of the operation of the enzyme is under discussion.<ref name="Steuber"/> NADPH binds to the polypeptide first, followed by the substrate.<ref name="review"/> The binding of NADPH induces a conformational change that involves a hinge-like movement of the surface loop (residues 213-217) so it covers part of the NADPH like a safety belt.<ref name="review"/> NADPH donates a hydride ion to the carbonyl carbon of the aldehyde. | The exact mechanism of the operation of the enzyme is under discussion.<ref name="Steuber"/> NADPH binds to the polypeptide first, followed by the substrate.<ref name="review"/> The binding of NADPH induces a conformational change that involves a hinge-like movement of the surface loop (residues 213-217) so it covers part of the NADPH like a safety belt.<ref name="review"/> NADPH donates a hydride ion to the carbonyl carbon of the aldehyde.<ref name="Steuber"/> The hydride transferred from NADPH to glucose comes from C-4 of the nicotinamide ring at the base of the hydrophobic cavity.<ref name="review"/> Most likely then the transfer of a proton from one of the neighbouring acidic residues to the intermediately formed substrate ion occurs.<ref name="Steuber"/> Tyr48, His110, and Cys298 are all within a proper distance of C-4 to be potential proton donors.<ref name="review"/> Evolutionary, thermodynamic, and molecular modeling evidence predicted that Tyr48 was the proton donor, which was later confirmed by mutagenesis studies.<ref name="review"/> Hydrogen-bonding interactions between the phenolic hydroxyl group of Tyr48 and the ammonium side chain of Lys77 are thought to help facilitate hydride transfer.<ref name="review"/> Lys 77 is salt linked to the carboxylate of Asp43.<ref name="review"/> After the reaction occurs and the alcohol product has been released another conformational change occurs to release the NADP+.<ref name="review"/> Kinetic studies have shown that the reorientation of the loop to release the NADP+ may be the rate-limiting step.<ref name="review"/> Thus, disturbing the interactions that stabilize the coenzyme binding can have dramatic effects on the maximum rate of the reaction.<ref name="review"/> | ||
==References== | ==References== | ||
<references/> | <references/> | ||
Latest revision as of 06:29, 1 April 2011
| This Sandbox is Reserved from January 10, 2010, through April 10, 2011 for use in BCMB 307-Proteins course taught by Andrea Gorrell at the University of Northern British Columbia, Prince George, BC, Canada. |
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Aldose Reductase (2IKH)Aldose Reductase (2IKH)
|
Information on aldose reductase is also available at Wikipedia
IntroductionIntroduction
is an enzyme that can reduce the aldehyde group of aldoses, aliphatic, aromatic aldehydes and some keto groups from aromatic and aliphatic ketones to their corresponding alcohol products using NADPH as a cofactor.[1][2] Aldose reductase is most well known in the first step of the polyol pathway of glucose metabolism (Figure 1).[1][2]
Polyol Pathway and DiabetesPolyol Pathway and Diabetes
As figure 1 shows, the polyol pathway involves the synthesis of fructose from glucose.[1][2] The first step of the pathway is the production of sorbitol from glucose, catalyzed by aldose reductase and using NADPH as a reducing cofactor.[1][2] The second step in the pathway is the production of fructose from sorbitol, catalyzed by sorbitol dehydrogenase using NAD+.[1][2] Under normal blood glucose levels most glucose is metabolized through glycolysis or the pentose phosphate pathway while only a small amount of glucose is metabolized through the polyol pathway.[2] Under the hyperglycemic conditions of diabetes the flux of glucose through the polyol pathway is increased.[1][2] This causes osmotic and oxidative stress, which can cause pathological interferences with cytokine signalling, regulation of apoptosis, and activation of kinase cascades.[1] For example, under increased glucose flux through the polyol pathway protein kinase C activivty increases, which causes smooth muscle cell proliferation of blood vessels in agreement with atherosclerosis.[1] This explains estimates that 75-80% of adults with diabetes die from complications of atherosclerosis.[1] Aldose reductase is also linked to long-term diabetic complications such as retinopathy, nephropathy, neuropathy, cataracts, and angiopathy.[1] Aldose reductase inhibitors are possible beneficial treatment options for diabetes.[1]
StructureStructure
Aldose reductase is a 36kDa aldo-keto reductase made of a single 315 amino acid residue polypeptide chain.[1][2] It has a (β/α)8- structural motif made of 8 parallel β-strands connected to 8 peripheral α-helices running anti-parallel to the β-strands.[1][2] Including the β-strands and α-helices of the TIM barrel, aldose reductase has a total of 10 . The catalytic active site is located at the C-terminal loop of the enzyme deeply buried inside the barrel core.[1][2] This site consists of residues that are most likely involved in the catalytic reaction (including residues Tyr48, Lys77, His110).[1] The cofactor is situated at the top of the barrel with the nicotinamide ring projecting down the center of the barrel and the pyrophosphate straddling the lip of the barrel.[2] Trp111 and the nicotinamide moiety of NADPH interact with the head group of most .[1] Hydrophobic contacts can be formed by the side-chains of Trp20, Val47, Trp79, and Trp219.[1]
Aldose Reductase Structure and InhibitorsAldose Reductase Structure and Inhibitors
Most inhibitors that bind tightly to aldose reductase have a polar group, which is usually a carboxylate, that is attached to a hydrophobic core.[2] Inhibitors bind with their polar head group oriented close to the pyridine ring and usually form hydrogen bonds with Tyr48, His110, and Tyr111.[2] Hydrophobic interactions between the inhibitor and the residues that line the active site help to stabilize the ternary enzyme-coenzyme-inhibitor complex. [2]
MechanismMechanism
The exact mechanism of the operation of the enzyme is under discussion.[1] NADPH binds to the polypeptide first, followed by the substrate.[2] The binding of NADPH induces a conformational change that involves a hinge-like movement of the surface loop (residues 213-217) so it covers part of the NADPH like a safety belt.[2] NADPH donates a hydride ion to the carbonyl carbon of the aldehyde.[1] The hydride transferred from NADPH to glucose comes from C-4 of the nicotinamide ring at the base of the hydrophobic cavity.[2] Most likely then the transfer of a proton from one of the neighbouring acidic residues to the intermediately formed substrate ion occurs.[1] Tyr48, His110, and Cys298 are all within a proper distance of C-4 to be potential proton donors.[2] Evolutionary, thermodynamic, and molecular modeling evidence predicted that Tyr48 was the proton donor, which was later confirmed by mutagenesis studies.[2] Hydrogen-bonding interactions between the phenolic hydroxyl group of Tyr48 and the ammonium side chain of Lys77 are thought to help facilitate hydride transfer.[2] Lys 77 is salt linked to the carboxylate of Asp43.[2] After the reaction occurs and the alcohol product has been released another conformational change occurs to release the NADP+.[2] Kinetic studies have shown that the reorientation of the loop to release the NADP+ may be the rate-limiting step.[2] Thus, disturbing the interactions that stabilize the coenzyme binding can have dramatic effects on the maximum rate of the reaction.[2]
ReferencesReferences
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19 Steuber H, Heine A, Klebe G. Structural and thermodynamic study on aldose reductase: nitro-substituted inhibitors with strong enthalpic binding contribution. J Mol Biol. 2007 May 4;368(3):618-38. Epub 2006 Dec 15. PMID:17368668 doi:10.1016/j.jmb.2006.12.004
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 2.14 2.15 2.16 2.17 2.18 2.19 2.20 2.21 2.22 2.23 Petrash JM. All in the family: aldose reductase and closely related aldo-keto reductases. Cell Mol Life Sci. 2004 Apr;61(7-8):737-49. PMID:15094999 doi:10.1007/s00018-003-3402-3