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| {{STRUCTURE_1vpr| PDB=1vpr | SCENE= }} | | {{STRUCTURE_2d1s| PDB=2d1s | SCENE= }} |
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| == Introduction == | | == Introduction == |
| | | Bioluminescence is utilized by several nocturnal japanese firely species during mate selection, with males and females illuminating equally. Several common signals appear to be used to communicate everything from "male awaiting a mate" to "female here". <ref name="main">PMID:8813052</ref> While the reaction is quite similiar to that of other bioluminescent luciferases, firefly luciferase has a unique structure in both the protein and luciferin required to produce the bioluminescence. In research, the firefly luciferase from Luciola cruciata is one of many commonly utilized for such purposes as such as sensing cellular ATP levels or visualizing the effects of a promoter sequence, among several others. |
| ''Lingulodinium polyedrum'', a marine dinoflagellate often responsible for red tide, posesses a unique luciferase enyzme. When mechanically stimulated, the organism uses this enzyme to produce a blue light, likely for use in quorum sensing. Other luciferase enzymes typically produce green-yellow to red light. Also, while all luciferase enzymes produce light through oxidation of luciferin, the biochemical mechanism by which this is achieved is different, so the lack of similarity to firefly and bacterial luciferases is expected.
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| In ''L. polyedrum'', the luciferase enzyme is a single polypeptide chain folded into 3 similar domains. Interestingly, all three domains appear to be distinct luciferase centres with their own catalytic activities <ref name="main">PMID:15665092</ref>
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| == Structure == | | == Structure == |
| | Generally, firefly luciferases have some similarities with Acyl-CoA ligases and some peptide synthetases despite having different cellular effects. In fixing the structure of L. cruciata luciferase, the analog of a potent aminoacyl-tRNA synthetases (DLSA) was successfuly utilized to represent a stable oxyluciferin intermediate.<ref name="structure">PMID:16541080 </ref>. |
| | The DLSA occupied the active site of the luciferase, which is composed of an α-helix (residues 248-260) and four short β-sheets (residues 286-289, 313-316, 339-342 and 351-353. Ile288 has been implicated as an important residue in determining the hydrophobicity of the active site environment, and through orientation of the product oxyluciferin, the bioluminescent colour. <ref name="structure" />. |
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| Composed of residues 868-1218, domain 3 (D3) also consists of a 20aa C-terminal unresolved domain. Containing 7 α-helices and 16 β-strands, D3 is further organized into subdomains. The main portion of the enzyme appears to be a β-barrel structure composed of 10 anti-parallel strands connected via a Gly rich sequence to a 3 helix bundle. This bundle is stabilized by a hydrophobic core region as well as a multitude of H-bonding patterns<ref name="main" />. The β-barrel structure actually has some homology with the human muscle fatty acid binding protein (m-FABP, pdb= 1HMT). Both are part of a "β-clam" subdomain family, responsible for binding of hydrophobic molecules. However, other known β-clam structures do not possess enzymatic activity<ref name="main" />.
| | [[Image:2d1s active site with ILE288.jpg | thumb |none | upright=3.0 | Figure 1: PYMOL image of 2D1S highlighting active site and Ile288, putatively identified in hydrophobic control of bioluminescent colour.]] |
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| [[Image:Structure_trihelix_barrel.jpg | thumb |none | upright=3.0 | Figure 1: Cropped Pymol image of 1vpr highlighting the β-barrel structure and tri-helix. The four histidine residues implied in pH-dependant activity regulation are highlighted in pink.]] | |
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| Note the position of the tri-helix in front of the β-barrel opening, blocking substrate entry. Under a pH of 8, the protonation states of the four histidines are thought to drive a conformational change that opens and expands the β-barrel. Interestingly, the four histidines(H899, H909, H924 and H930) are conserved in another dinoflagellate, ''Pyrocystis lunula''<ref name="papertwo">PMID:11747464</ref>. This seems to suggest a pH-dependant luciferase contol mechanism similiar to the proposed mechanism in ''L. polyedrum''. While related at the primary structure level, the structure of ''P. lunula'' luciferase has yet to be solved, so further structural similarities cannot be easily resolved.
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| == Luciferase Reaction ==
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| Typically, luciferases produce light through a high energy complex with a luciferin cofactor, and Mg-ATP. The structure of luciferin is different from organism to organism, and in ''L. polyedrum'', is a chlorophyll-derived open-tetrapyrrole. Below is the dinoflagellate luciferase reaction, showing the oxidation site.
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| [[Image:Luciferase_reaction.jpg]]
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| ''Image courtesy of L. Wayne Schultz.''
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| == Related Links == | | == Related Links == |
| [http://www.pymol.org/ Pymol molecular viewer] | | [http://www.pymol.org/ Pymol molecular viewer] |
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| [http://www.pdb.org/pdb/explore/explore.do?structureId=1VPR Protein Data Bank file on 1VPR] | | [http://www.pdb.org/pdb/explore/explore.do?structureId=2D1S Protein Data Bank file on 2D1S] |
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| | [http://www.ncbi.nlm.nih.gov/protein/CAA59282.1 NCBI protein entry on ''Photinus pyralis'' luciferase, the american firefly] |
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| == References == | | == References == |
| <references /> | | <references /> |