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| ==NrdH of ''Mycobacterium tuberculosis''== | | {{Sandbox_Reserved_Butler_CH462_Sp2015_#}}<!-- PLEASE ADD YOUR CONTENT BELOW HERE --> |
| | ==Your Protein Name here== |
| | <StructureSection load='1stp' size='340' side='right' caption='Caption for this structure' scene=''> |
| | This is a default text for your page ''''''. Click above on '''edit this page''' to modify. Be careful with the < and > signs. |
| | You may include any references to papers as in: the use of JSmol in Proteopedia <ref>DOI 10.1002/ijch.201300024</ref> or to the article describing Jmol <ref>PMID:21638687</ref> to the rescue. |
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| <StructureSection load='4K8M' size='350' side='right' caption='NrdH of ''Mycobacterium tuberculosis''' (PDB entry [[4K8M]])' scene=''>
| | == Biological Function == |
| ==Introduction==
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| [http://proteopedia.org/wiki/index.php/4k8m NrdH] is a redox protein and is part of a family of redox proteins. The other proteins that maintain the redox balance of NrdH are three [http://en.wikipedia.org/wiki/Thioredoxin thioredoxin] and three [http://en.wikipedia.org/wiki/Glutaredoxin glutaredoxins]-like proteins. Prokaryotes typically maintain redox homeostasis through low-molecular weight thiols (glutathione) and through proteins involved in disulfide exchange (thioredoxins)<ref name="Phulera" />. NrdH is found in many types of bacteria, such as [http://www.nature.com/nature/journal/v393/n6685/full/393537a0.html ''Mycobacterium tuberculosis'']. This bacteria causes the disease [http://en.wikipedia.org/wiki/Tuberculosis tuberculosis] <ref name="Cole"> DOI: 10.1038/31159</ref>.
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| ===Background=== | | == Structural Overview == |
| [http://www.mayoclinic.org/diseases-conditions/tuberculosis/basics/definition/con-20021761 Tuberculosis (TB)] is a contagious, fatal disease if not treated properly. It affects the lungs mostly, but can have detrimental affects on other organs of the body as well. TB bacteria can be latent and live inside the body in a dormant state without causing any symptoms. When it becomes active, it results in symptoms of bad coughing, chest pain, and others. It is typically treated with several drugs taken for 6-9 months.It was the leading cause of death in the United States in the past, and it can be spread through the air from one person to another by coughing, sneezing, or speaking <ref>Tuberculosis (TB). ''PubMed Health''. Retrieved from http://www.ncbi.nlm.nih.gov/pubmedhealth/PMHT0024668/</ref>.
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| ==Structure== | | == Mechanism of Action == |
| [[Image:Image_2_(2).png|350px|left|thumb|'''Figure 1:'''Binding site specific for aromatic amino acids. The hole that is located in the center of this image of NrdH shows the binding site.]]
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| The <scene name='69/694226/Tertiary_structure/4'>tertiary structure</scene> of NrdH has a thioredoxin fold with 79 residues with a glutaredoxin-like sequence. Unlike glutaredoxins, NrdH of ''Mycobacterium tuberculosis'' can accept electrons from thioredoxin reductase<ref name="Phulera" />. It contains two bound ligands, three alpha helices, and four beta sheets. The two ligands are colored by element, red representing oxygen and gray representing carbon. The binding site of NrdH is specific for aromatic amino acids. The image on the left shows the specific binding site. The specificity for aromatic amino acids is vital because aromatic-aromatic interactions have shown to have great importance for protein folding, ligand binding, and protein stability <ref name="Lanzarotti">DOI: 10.1021/ci200062e</ref>.
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| NrdH has a typical thioredoxin fold and is a monomer that has the ability to form a stable dimer when there is a high concentration of protein. The thioredoxin fold composes three alpha helices with four beta sheets.
| | == Zinc Ligand(s) == |
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| ===Conserved Motifs=== | | == Other Ligands == |
| Members of the NrdH family are typically characterized by CVQC and WSGFRP <scene name='69/694226/Conserved_motifs/2'>conserved sequence motifs</scene>.
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| [[Image:Conserved Motifs.png|300px|left|thumb|'''Figure 2:'''The two conserved sequence motifs: CVQC and WSGFRP have a network of hydrogen bonding that stabilizes the redox active site in NrdH. This hydrogen bonding network allows for specific interactions with substrates.]]
| | This is a sample scene created with SAT to <scene name="/12/3456/Sample/1">color</scene> by Group, and another to make <scene name="/12/3456/Sample/2">a transparent representation</scene> of the protein. You can make your own scenes on SAT starting from scratch or loading and editing one of these sample scenes. |
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| The <scene name='69/694226/Cvqc_motif/3'>CVQC motif</scene>, is an active site and it is located at the N terminus of the first alpha helix<ref name="Laer" />. It is one of the best characterized redox motifs within the thioredoxin-like proteins. The N-terminal cysteine acts as a nucleophile and the C-terminal cysteine acts as the resolving cysteine. Valine is known to be exposed to the solvent. The hydrogen bonding network is important for stability to the redox active site <ref name="Phulera" />.
| | </StructureSection> |
| | | == References == |
| The <scene name='69/694226/Wsgfrp_conserved_motif/3'>WSGFRP motif</scene> is stabilized by glutamine of the CVQC motif and phenylalanine is exposed to the solvent. Phe-64 and Val-12 with Ala-16 and Ala-20 create a distinct hydrophobic patch that is exposed to the solvent. This patch is of functional significance that could potentially interact with the C-terminus of RNR<ref name="Phulera" />.
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| In all members of the NrdH family, Arg-68 is a highly conserved residue. This residue hydrogen bonds with the main carbonyl oxygen of His-60, which is located before the WSGFRP motif. This suggests that the interaction between Arg-68 and His-60 may be of structural significance. In an alternate conformation of Arg-68, the guanidinyl group of Arg-68 forms a salt bridge with Asp-59. The hydrogen bonds and salt bridge work together to stabilize the WSGFRP motif <ref name="Phulera" />.
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| A buried water molecule binds with the WSGFRP motif. This water is believed to be one of the structural signatures of NrdH proteins. The hydrogen bonding network of the CVQC and WSGFRP motifs also involves the water molecule, and this may suggest that this region is important in the evolution of NrdH <ref name="Phulera" />.
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| ==Function==
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| The main function of NrdH is to act as a reducing partner of class 1B ribonucleotide reductase and for ribonucleotide reduction (RR) and is thought to supply electrons for this biochemical reaction. RR is one of the most fundamental biochemical processes that is required for DNA based life form to exist. Ribonucleotide reductases (RNRs) produce deoxyribonucleotides, which are precursors for DNA synthesis. NrdH is able to accept electrons from ''M. tuberculosis'' thioredoxin reductase and is able to reduce the disulfide bonds that are present in insulin <ref name="Phulera" />.
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| NrdH redoxins are small reductases, and they contain similar amino acid sequences to glutaredoxins and [http://en.wikipedia.org/wiki/Mycoredoxin mycoredoxins]. However, NrdH redoxins are different because of their thioredoxin-like activity. Their main function is to act as the electron donor for class 1b [http://en.wikipedia.org/wiki/Ribonucleotide_reductase ribonucleotide reductases], which are important for the conversion of [http://en.wikipedia.org/wiki/Ribonucleotide ribonucleotides] to [http://en.wikipedia.org/wiki/Deoxyribonucleotide deoxyribonucleotides] <ref name="Laer">DOI: 10.1074/jbc.M112.392688</ref>. The process of ribonucleotide reduction is one of the most fundamental biochemical processes that is required for the existence of DNA-based life. It is the only de novo pathway to synthesize deoxyribonucleotides. Deoxyribonucleotides are the building blocks of DNA and are synthesized from ribonucleotides by reducing the 2’OH in a radical based reaction. The deoxyribonucleotides are then used as precursors for the process of DNA synthesis. This reaction is catalyzed by ribonucleotide reductases <ref name="Phulera">DOI: 10.1021/bi400191z</ref>.
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| ===Ribonucleotide Reductases (RNRs)===
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| All RNRs are related because they are necessary for all living cells, with the exception of a couple types of parasites and obligate endosymbionts. This is evident due to the catalytic core, which is structurally conserved across all extant RNRs. RNRs are essential for the processes of DNA replication and repair <ref name="Lundin">DOI: 10.1186/1471-2148-10-383</ref>.
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| There are three classes of RNRs. These classes are divided based on the mechanism of radical generation in the reaction.
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| [[Image:Classes_of_ribonucleotide_reductases_(RNR).png]]
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| Class I enzymes reduce nucleotide 5’-diphosphates, while the other 2 classes reduce ribonucleotide 5’-triphosphates <ref name="Phulera" />. Class I RNRs are oxygen-dependent enzymes that contain a di-iron cluster <ref name="Laer" />.
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| Class 1 RNRs generate a [http://en.wikipedia.org/wiki/Tyrosine tyrosyl] [http://en.wikipedia.org/wiki/Radical_(chemistry) radical] in another subunit, which is NrdB for class 1a and NrdF in class 1b. The tyrosyl radical is then transferred to the catalytic subunit, which is NrdA in class Ia and NrdE in class 1b <ref name="Lundin" />.
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| At the end of each cycle of ribonucleotide reduction, the ribonucleotide reductase needs to be reduced in order to be ready for the next reduction cycle. For a class 1a RNR, an external cofactor, such as a glutaredoxin or thioredoxin, performs this reduction step. For class 1b RNRs, this cofactor is known as NrdH. NrdH contains a glutaredoxin-like sequence but behaves like a thioredoxin <ref name="Phulera" />.
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| ==Relevance==
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| [[Image:Image_7_(1).png|300px|right|thumb|'''Figure 3:'''Sequence alignment of NrdH from ''Mycobacterium tuberculosis'', ''Corynebacterium glutamicum'', and ''Echerichia coli''. The thioredoxin fold is found in NrdH of ''M. tuberculosis'', and it is similar to NrdH of other organisms.]]
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| NrdH of ''M. tuberculosis'' has a thioredoxin fold, which was predicted due to the fact that NrdH of other organisms have a similar thioredoxin fold. This was shown by superimposing the structure of NrdH of multiple organisms. These superimpositions are important because it allows for analyzation of the similarities and differences of NrdH of ''M. tuberculosis'' with glutaredoxin and thioredoxin. There are slight changes in the series of sequence which in turn leads to a change in the tertiary structure. In the process of modeling NrdH with the glutaredoxin-1b RNR C-terminal peptide complex, it was apparent that the peptide bonds were slightly different within the class 1b RNRs. This also provided more evidence for the specificity of NrdH to NrdE. Genes that encode for NrdE and NrdF are essential for growth, and RR might be an attractive biochemical pathway for antimycobacterial drug discovery. Organisms that depend solely on class 1b RNR could potentially contain the essential genes and serve as potential drug targets for treating tuberculosis <ref name="Phulera" />.
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| ==References== | |
| <references/> | | <references/> |
| </StructureSection>
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