Molecular Playground/Hsp70-Hsp90: Difference between revisions
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<applet load='1elr' size='400' color='white' frame='true' align='right' caption='Dihydrofolate Reductase (DHFR)''/> | |||
Molecular Playground banner: DHFR, a central player in the synthesis of nucleic acids and amino acids | |||
<scene name='User:Karan_Hingorani/sandbox_2/Banner_1/1'>E. coli Dihydrofolate Reductase bound to Dihydrofolate and NADP+</scene> | |||
Dihydrofolate Reductase (DHFR) is a crucial metabolic enzyme whose function is to reduce Dihydrofolate to Tetrahydrofolate, which can then be incorporated into the synthesis of Purines and amino acids. DHFR is classified as an oxidoreductase, which uses NADP+ as the electron acceptor (EC: 1.5.1.3). It is ubiquitously found and is now a popular target for anticancer drugs and antibiotics. <scene name='User:Karan_Hingorani/sandbox_2/Apo_dhfr/5'>Apo-DHFR</scene> free of any of its ligands is displayed here.[http://www.ncbi.nlm.nih.gov/pubmed/2185835?dopt=Abstract] | |||
===Structure=== | |||
E.coli DHFR is a small 159 amino acid protein approximately 18kDa. It has an a/b structure with eight central B strands and four helices. The protein can be thought to be made up of two subdomains, divided by the active site cleft. The <scene name='User:Karan_Hingorani/sandbox_2/Ade_loop_1/1'>Adenosine binding loop</scene> which consists of residues 38-88 and the major subdomain comprised of about 100 residues. Three loops can be found in the major subdomain and they make up about 50% of this domain. They are the <scene name='User:Karan_Hingorani/sandbox_2/Met20_loop_1/1'>Met20 loop</scene> (residues 9-24), the <scene name='User:Karan_Hingorani/sandbox_2/Fg_loop_1/1'>F-G loop</scene> (residues 116-132)and the <scene name='User:Karan_Hingorani/sandbox_2/Gh_loop_1/1'>G-H loop</scene> (residues 142-150). The Met20 loop assumes different conformations during catalysis and accomodation of ligands is made possible by the 'hinge bending' motion about Lys 38 and Val 88 of the Adenosine binding domain.[http://www.ncbi.nlm.nih.gov/pubmed/15139807] | |||
===Catalysis=== | |||
DHFR catalyzes the reduction of 7,8-dihydrofolate to 5,6,7,8-tetrahydrofolate using reduced Nicotinamide Adenine Dinucleotide Phosphate (NADPH). This system has been key model to decipher enzyme catalysis and the intermediates of the catalytic cycle have been identified by crystallography. CPMG relaxation NMR experiments have also revealed that intermediates in the catalytic cycle exist in equilibrium with the preceding or following intermediate. Thus the binding of ligands seems to happen via a conformational selection rather than the traditional view of induced fit which is used to explain conformation change on ligand binding.[http://www.sciencemag.org/content/313/5793/1638.short]. <scene name='User:Karan_Hingorani/sandbox_2/Lig_bound_1/1'>Holo DHFR</scene> shows the ligands Dihydrofolate and NADP+ positioned in the active site cleft.[http://www.ncbi.nlm.nih.gov/pubmed/2185835?dopt=Abstract] | |||
===Drug Target=== | |||
Since DHFR is so critically positioned in the metabolic homeostasis of all organsims it has been the target of choice for anti microbial and anti cancer therapy. Inhibitors of this enzyme are essentially folate mimics, methotrexate which was first designed to inhibit <scene name='User:Karan_Hingorani/sandbox_2/Humandhfr_nad_metho_1/1'>Human DHFR</scene> and used as therapy for cancer and autoimmune disorders. Another folate mimic Trimethoprim was developed as an anti bacterial agent, having much more binding specificity to bacterial DHFR than its mammalian counterpart. Both drugs bind in the active site of the enzyme and are irreversibly bound thus ablating enzyme activity.[http://www.ncbi.nlm.nih.gov/pubmed/3054871] [http://www.ncbi.nlm.nih.gov/pubmed/15681865?dopt=Abstract]. | |||
===PDB structures=== | |||
[[5dfr]] - Apo E.coli DHFR | |||
[[7dfr]] - E.coli DHFR bound to Folate and NADP+ | |||
[[1u72]] - Human DHFR bound to NADP+ and Methotrexate | |||
There are several other structures for DHFR from Human, E.coli and other species but are not shown here. You may refer to the pdb website for those. [http://www.pdb.org/pdb/results/results.do?qrid=FE767C1F&tabtoshow=Current] | |||
===See Also=== | |||
The wikipedia link on DHFR is also pretty useful for a general background.[[http://en.wikipedia.org/wiki/Dihydrofolate_reductase]] | |||
===References=== | |||
1. Bystroff C. et al. Biochemistry 1990 | |||
2. Schnell JR. et al. Annu Rev Biophys Biomol Struct. 2004 | |||
3. Boehr DD. et al. Science 2006 | |||
4. Bystroff C. et al. Biochemistry 1990 | |||
5. Dauber-Osguthorpe P et al. Proteins 1988 | |||
6. Cody V. et al. Acta Crystallogr D Biol Crystallogr. 2005 | |||