Sandbox 156: Difference between revisions
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[[Image:Picture2.jpg|500x400 px|center]] | [[Image:Picture2.jpg|500x400 px|center]] | ||
In the first step of the reaction, Histidine-195 abstracts a proton from the 3-hydroxyl of chloramphenicol, promoting a nucleophilic attack from the oxyanion to the thioester bond of the acetyl-CoA. The intermediate produced, 3-acetylchloramphenicol, then rearranges non-enzymatically to 1-acetylchloramphenicol. Regeneration of the 3-hydroxyl allows another round of CAT III catalyzed nucleophilic attack and a 1,3-diacetylchloramphenicol product is formed | In the first step of the reaction, Histidine-195 abstracts a proton from the 3-hydroxyl of chloramphenicol, promoting a nucleophilic attack from the oxyanion to the thioester bond of the acetyl-CoA. The intermediate produced, 3-acetylchloramphenicol, then rearranges non-enzymatically to 1-acetylchloramphenicol. Regeneration of the 3-hydroxyl allows another round of CAT III catalyzed nucleophilic attack and a 1,3-diacetylchloramphenicol product is formed<ref>PMID:2015231</ref>. | ||
==Structure== | ==Structure== | ||
The general structure of CAT III is dominated by a six stranded antiparallel <scene name='Sandbox_156/Scene_4/4'>β-sheet</scene> and 5 <scene name='Sandbox_156/Scene_4/3'>α-helices</scene> stacked against the ends and face of the protein, forming a structure known as an "open-faced sandwhich" | The general structure of CAT III is dominated by a six stranded antiparallel <scene name='Sandbox_156/Scene_4/4'>β-sheet</scene> and 5 <scene name='Sandbox_156/Scene_4/3'>α-helices</scene> stacked against the ends and face of the protein, forming a structure known as an "open-faced sandwhich"<ref>PMID: 3288984</ref>. | ||
===The Chloramphenicol Binding Site=== | ===The Chloramphenicol Binding Site=== | ||
The <scene name='Sandbox_156/Scene_3/1'>active site</scene> of CAT III is lined with generally hydrophobic residues, allowing only 2 hydrogen bonds with the substrate. A third hydrogen bond is mediated through a <scene name='Sandbox_156/Scene_4/2'>bridging hydrogen bond</scene> between the the 1-hydroxyl of chloramphenicol and the hydroxyl of tyrosine-174 by a water molecule. | The <scene name='Sandbox_156/Scene_3/1'>active site</scene> of CAT III is lined with generally hydrophobic residues, allowing only 2 hydrogen bonds with the substrate. A third hydrogen bond is mediated through a <scene name='Sandbox_156/Scene_4/2'>bridging hydrogen bond</scene> between the the 1-hydroxyl of chloramphenicol and the hydroxyl of tyrosine-174 by a water molecule<ref>PMID:2015231</ref>. | ||
{{STRUCTURE_4CLA | PDB=4CLA | Scene=Sandbox_156/Scene_1/1}} | {{STRUCTURE_4CLA | PDB=4CLA | Scene=Sandbox_156/Scene_1/1}} | ||
