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Revision as of 00:28, 22 January 2010
2010 Pingry S.M.A.R.T. Team, Protein Engineering; AKR's for Biofuel Cells2010 Pingry S.M.A.R.T. Team, Protein Engineering; AKR's for Biofuel Cells
The 2010 Pingry School S.M.A.R.T. Team (Students Modeling A Research Topic) is working with Dr. Scott Banta and graduate student Elliot Campbell at Columbia University to learn about enzymes being engineered for use in biofuel cells. Features being engineered into these enzymes include (1) self-assembly into hydrogels, (2) alternate cofactor use, and (3) broader substrate specificity. AdhD alcohol dehydrogenase from the thermophile Pyrococcus furiosus is one of the enzymes being engineered with these features by the Banta Lab. AdhD is a member of the aldo-keto reductase (AKR) family of oxidoreductases. Taking advantage of its innate thermostable properties, the Banta Lab is engineering AdhD for use in biofuel cells.
The logical design and engineering of AdhD is based partially on the solved structures of other enzymes belonging to the AKR family of enzymes. Structures of mutants that bind alternate cofactors and those bound to its substrate provide insight into how to engineer AdhD and other enzymes of use in a biofuel cell. The 2010 Pingry S.M.A.R.T. Team is producing physical models of various AKR's that highlight the enzymes' structural and functional characteristics that are relevant to the Banta Lab's work.
What are S.M.A.R.T. Teams?What are S.M.A.R.T. Teams?
"S.M.A.R.T. Teams (Students Modeling A Research Topic) are teams of high school students and their teachers who are working with research scientists to design and construct physical models of the proteins or other molecular structures that are being investigated in their laboratories. SMART Teams use state-of-the-art molecular design software and rapid prototyping technologies to produce these unique models." -from the MSOE Center for BioMolecular Modeling Website.
The S.M.A.R.T. Team program was supported in part by Grant Number 1 R25 RR022749-01 from the National Center for Research Resources (NCRR), a component of the National Institutes of Health (NIH), awarded to the Center for BioMolecular Modeling.
AdhD and Self-assembly into hydrogelsAdhD and Self-assembly into hydrogels
Cofactor specificityCofactor specificity
Modifying cofactor specificity, 2,5-diketo-d-gluconic acid reductaseModifying cofactor specificity, 2,5-diketo-d-gluconic acid reductase
2,5 Diketo-D-Gluconic acid reductase is found in corynbacterium and is part of the Aldo Keto Reductase family of enzymes. It exists in two variants: DKGR A and DKGR B; however, we talk about DKGR A here due to its higher thermal stability. 2,5 DKGR is an important enzyme in the production of vitamin C, one of the most important chemicals manufactured in the world. 2,5 DKGR does this by catalyzing the reduction of 2,5-diketo-D-gluconic acid (2,5 DKG) to 2-Keto-L-gluconic acid (2-KLG); a precursor to vitamin C. It is commercially less expensive to use NADH as a cofactor (as opposed to NADPH) and the catalyzation of 2,5 DKG into 2-KLG as well as being more abundant.
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PDB ID: 1a80, 2,5-diketo-d-gluconic acid reductase with NADPH (wild-type)PDB ID: 1a80, 2,5-diketo-d-gluconic acid reductase with NADPH (wild-type)
Design description
Cofactor (NADPH) shown in wireframe and colored CPK.
Other residues highlighted by displaying sidechain:
interacts with phosphate group of NADPH. These are changed in the mutant form in order to accommodate for the cofactor NADH.
Not shown:
two residues conserved in all AKR proteins.
Proton donor in AKR and part of catalytic triad that is conserved in all AKR proteins.
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PDB ID: 1m9h, Mutant 2,5-diketo-d-gluconic acid reductase with NADH (mutant)PDB ID: 1m9h, Mutant 2,5-diketo-d-gluconic acid reductase with NADH (mutant)
Design description
Red and blue highlight the (alpha/beta)8 barrel structure found in all AKR's.
Mutant cofactor (NADH) shown in wireframe and colored CPK.
The backbone of the four residues changed between WT and NADP-binding mutant are colored orange (Lys232Gly, Phe22Tyr, Arg238His, Ala272Gly).
is important because Gly has no sidechain so there is nothing to interact with the absent phosphate group.
reduces the Km for both NADPH and NADH.
forms a pi-stacking interaction to stabilize the AKR with the cofactor.
improves the kinetic properties by making it easier for the substrate to bind with the substrate or by improving the kinetics of cofactor binding and release.
Other residues highlighted by displaying sidechain:
pi-stacking interaction with the nicotinamide ring of the cofactor that stabilizes the reaction.
Not shown:
Ala47 and Trp77; residues conserved in AKR's
Tyr50; Proton donor in AKR and part of catalytic triad
Inherent dual cofactor use, Xylose reductaseInherent dual cofactor use, Xylose reductase
Xylose reductase is an unusual protein from the aldo-keto reductase superfamily in that the wild type is able to efficiently utilize both NADH and NADPH in its reduction of the 5 carbon sugar xylose into xylitol. Normally found in the yeast Candida tenuis, it functions biologically as a homodimer unlike the majority of AKR proteins. While Dr. Banta is not actively researching this protein, Xylose Reductase's dual substrate specificity has influenced his engineering of AdhD. Because of its ability to change the conformation of two major loops, which enable different side chain conformations, Xylose Reductase can accomodate both the presence and absence of a phosphate in the cofactor.
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PDB ID: 1k8c, Xylose reductase with NADP+PDB ID: 1k8c, Xylose reductase with NADP+
Pink and blue highlight the (alpha/beta)8 barrel structure of AKR's. Cofactor (NADP+) shown in wireframe and colored CPK.
Ser275- interacts with an oxygen on the NADP ribose’s phosphate group but does not interact with the NAD cofactor
Asn276-hydrogen bonding interactions with the different cofactors change when the cofactor changes
Arg280-changes position and interacts differently with the two types of cofactors.
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PDB ID: 1mi3, Xylose reductase with NAD+PDB ID: 1mi3, Xylose reductase with NAD+
Substrate specificitySubstrate specificity
A structure of an AKR with its substrate, 3-alpha-hydroxysteroid dihydrodiol dehydrogenaseA structure of an AKR with its substrate, 3-alpha-hydroxysteroid dihydrodiol dehydrogenase
A key component of Dr. Banta’s work is engineering AdhD to accept a broad range of substrates. This is a crucial component of his work, because this enzyme will be required to act upon a wide range of substrates when it is used within a practical biofuel cell. Rat liver 3-alpha-hydroxysteroid dihydrodiol dehydrogenase demonstrates how an enzyme is specific to certain substrates and therefore help show what might be done to broaden the specificity of an enzyme. The function of this enzyme within the rat liver is to regulate/ inactivate steroid hormones. The enzyme does this is by reducing the steroid’s (testosterone) C3 ketone group. The interactions within the active site and testosterone are very specific, because of the structure and positioning of the residues within the cavity. This information is important, because it will help show what might be done to adhd to broaden its substrate specificity.
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PDB ID: 1lwi, Rat liver 3-alpha-hydroxysteroid dihydrodiol dehydrogenase with NADP+ cofactorPDB ID: 1lwi, Rat liver 3-alpha-hydroxysteroid dihydrodiol dehydrogenase with NADP+ cofactor
NADPH (cofactor) is colored CPK.
The catalytic triad is at the distal end of the pocket.
Gln190, Asn167, Ser166 form hydrogen bonds with the nicotinamide ring.
Tyr55 acts as acid, donates proton to steroid-->Tyr55 forms hydrogen bond to Lys84 to stabilize-->Lys84 forms salt link to Asp50 for further stability
Dark Grey highlights the beta barrel and helix structure. The barrel consists of eight parallel beta strands and eight anti-parallel alpha helices. The bottom is sealed by two antiparallel beta strands (6-10 and 13-18).
The top contains two solvent exposed loops (loop A: 116-142 and loop B: 217-235)
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PDB ID: 1afs, Rat liver 3-alpha-hydroxysteroid dihydrodiol dehydrogenase with cofactor and testosteronePDB ID: 1afs, Rat liver 3-alpha-hydroxysteroid dihydrodiol dehydrogenase with cofactor and testosterone
Testosterone (substrate) and NADPH (cofactor) are colored CPK.
Non-polar cavity for substrate binding is colored CPK. Leu54, Tyr55, Trp86, Phe118, Phe129, and Tyr216 are hydrophobic amino acids found in the pocket. The catalytic triad is at the distal end of the pocket.
Orange highlights the cofactor specificity sidechains. Gln90, Asn167, Ser166 form hydrogen bonds with the nicotinamide ring.
Green highlights the safety belt mechanism in 1AFS.
Cyan highlights the catalytic triad: Tyr55, Asp50, and Lys84. Tyr55 acts as acid, donates proton to steroid-->Tyr55 forms hydrogen bond to Lys84 to stabilize-->Lys84 forms salt link to Asp50 for further stability
Dark Gray highlights the beta barrel and helix structure. The barrel consists of eight parallel beta strands and eight antiparallel alpha helices. The bottom is sealed by two antiparallel beta strands (6-10 and 13-18). The top contains two solvent exposed loops (loop A: 116-142 and loop B: 217-235)
Purple and Blue highlight the two solvent exposed loops (Purple: Loop A, Blue: Loop B)
ReferenceReference
Biofuel cells
- ↑ Minteer SD, Liaw BY, Cooney MJ. Enzyme-based biofuel cells. Curr Opin Biotechnol. 2007 Jun;18(3):228-34. Epub 2007 Mar 30. PMID:17399977 doi:10.1016/j.copbio.2007.03.007
- ↑ Davis F, Higson SP. Biofuel cells--recent advances and applications. Biosens Bioelectron. 2007 Feb 15;22(7):1224-35. Epub 2006 Jun 16. PMID:16781864 doi:10.1016/j.bios.2006.04.029
Aldo-keto reductases
- ↑ Sanli G, Dudley JI, Blaber M. Structural biology of the aldo-keto reductase family of enzymes: catalysis and cofactor binding. Cell Biochem Biophys. 2003;38(1):79-101. PMID:12663943 doi:10.1385/CBB:38:1:79
AdhD and hydrogels
- ↑ Wheeldon IR, Campbell E, Banta S. A chimeric fusion protein engineered with disparate functionalities-enzymatic activity and self-assembly. J Mol Biol. 2009 Sep 11;392(1):129-42. Epub 2009 Jul 3. PMID:19577577 doi:10.1016/j.jmb.2009.06.075
Modifying cofactor specificity, 2,5-diketo-d-gluconic acid reductase
- ↑ Kavanagh KL, Klimacek M, Nidetzky B, Wilson DK. Structure of xylose reductase bound to NAD+ and the basis for single and dual co-substrate specificity in family 2 aldo-keto reductases. Biochem J. 2003 Jul 15;373(Pt 2):319-26. PMID:12733986 doi:10.1042/BJ20030286
Innate dual cofactor use, Xylose reductase
- ↑ Kavanagh KL, Klimacek M, Nidetzky B, Wilson DK. Structure of xylose reductase bound to NAD+ and the basis for single and dual co-substrate specificity in family 2 aldo-keto reductases. Biochem J. 2003 Jul 15;373(Pt 2):319-26. PMID:12733986 doi:10.1042/BJ20030286
Substrate binding by an AKR, Rat liver 3 alpha-hydroxysteroid dihydrodiol dehydrogenase
- ↑ Bennett MJ, Schlegel BP, Jez JM, Penning TM, Lewis M. Structure of 3 alpha-hydroxysteroid/dihydrodiol dehydrogenase complexed with NADP+. Biochemistry. 1996 Aug 20;35(33):10702-11. PMID:8718859 doi:10.1021/bi9604688