Aminoacyl tRNA synthetase: Difference between revisions
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=== Aminoacylation of tRNAs === | === Aminoacylation of tRNAs === | ||
[[TRNA|tRNA]] molecules joined to their corresponding [[Amino acid|amino acid]] are called aminoacyl tRNAs, this reaction is called [[Aminoacylation|aminoacylation]] and is a 2 step reaction driven by [[ATP|ATP]] and catalysed by aminoacyl tRNA synthetases. [[Amino acid|Amino acids]] are activated by [[Adenylation|adenylation]] by reacting with [[ATP|ATP]] to form [[Aminoacyl adenylate|aminoacyl adenylate (aminoacyl AMP)]], a high energy intermediate, and [[Pyrophosphate|pyrophosphate]]. The next step is the transfer of the aminoacyl group from [[Aminoacyl adenylate|aminoacyl adenylate]] to a [[TRNA|tRNA]] molecule to make an aminoacyl tRNA and release [[AMP|AMP<ref> | [[TRNA|tRNA]] molecules joined to their corresponding [[Amino acid|amino acid]] are called aminoacyl tRNAs, this reaction is called [[Aminoacylation|aminoacylation]] and is a 2 step reaction driven by [[ATP|ATP]] and catalysed by aminoacyl tRNA synthetases. [[Amino acid|Amino acids]] are activated by [[Adenylation|adenylation]] by reacting with [[ATP|ATP]] to form [[Aminoacyl adenylate|aminoacyl adenylate (aminoacyl AMP)]], a high energy intermediate, and [[Pyrophosphate|pyrophosphate]]. The next step is the transfer of the aminoacyl group from [[Aminoacyl adenylate|aminoacyl adenylate]] to a [[TRNA|tRNA]] molecule to make an aminoacyl tRNA and release [[AMP|AMP]] <ref>Berg JM, Tymoczko JL, Stryer L (2007) Biochemistry p862, 6th edition, WH Freeman, New York</ref>. | ||
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=== Aminoacyl tRNA synthetases === | === Aminoacyl tRNA synthetases === | ||
[[Aminoacylation|Aminoacylation must]] be highly specific as the correct [[Amino acid|amino acids]] must be on the correct [[TRNA|tRNAs]] for a functional [[Protein|protein]] to be synthesised. Aminoacyl tRNA synthetases must be able to distinguish not only between approximately 40 similarly shaped [[TRNA|tRNA]] molecules, but also very similar [[Amino acid|amino acids]] acids such as [[Serine|serine]], [[Threonine|threonine]] and [[Valine|valine]]. These [[Enzyme|enzymes]] use particular 'identity elements' in different [[TRNA|tRNAs]], which can be located in the [[Anticodon|anticodon]] region, [[Amino acid acceptor stem|amino acid acceptor stem]], variable arm, or a mixture of them. In order to discriminate between different [[Amino acid|amino acids]], aminoacyl tRNA synthetases have a proofreading mechanism. They have an acylation (activation) site and some also have an editing site (not all tRNA synthetases have this, only when the [[Enzyme|enzyme]] needs an additional mechanism to distinguish between amino acids). The acylation site rejects [[Amino acid|amino acids]] which are too large to fit in the site, and in doing so will accept the correct [[Amino acid|amino acid]], but also other [[Amino acid|amino acids]] which are smaller than the correct one. [[Amino acid|Amino acids]] which fit into the editing site are [[Hydrolysis|hydrolytically]] cleaved as they are identified as being smaller than the correct [[Amino acid|amino acid]], so only the correct [[Amino acid|amino acid will]] remain. This proofreading mechanism greatly improves[[Protein|protein synthesis]] fidelity so mistakes are less than 1 in 10,000 [[Amino acid|amino acids<ref>Biochemistry | [[Aminoacylation|Aminoacylation must]] be highly specific as the correct [[Amino acid|amino acids]] must be on the correct [[TRNA|tRNAs]] for a functional [[Protein|protein]] to be synthesised. Aminoacyl tRNA synthetases must be able to distinguish not only between approximately 40 similarly shaped [[TRNA|tRNA]] molecules, but also very similar [[Amino acid|amino acids]] acids such as [[Serine|serine]], [[Threonine|threonine]] and [[Valine|valine]]. These [[Enzyme|enzymes]] use particular 'identity elements' in different [[TRNA|tRNAs]], which can be located in the [[Anticodon|anticodon]] region, [[Amino acid acceptor stem|amino acid acceptor stem]], variable arm, or a mixture of them. In order to discriminate between different [[Amino acid|amino acids]], aminoacyl tRNA synthetases have a proofreading mechanism. They have an acylation (activation) site and some also have an editing site (not all tRNA synthetases have this, only when the [[Enzyme|enzyme]] needs an additional mechanism to distinguish between amino acids). The acylation site rejects [[Amino acid|amino acids]] which are too large to fit in the site, and in doing so will accept the correct [[Amino acid|amino acid]], but also other [[Amino acid|amino acids]] which are smaller than the correct one. [[Amino acid|Amino acids]] which fit into the editing site are [[Hydrolysis|hydrolytically]] cleaved as they are identified as being smaller than the correct [[Amino acid|amino acid]], so only the correct [[Amino acid|amino acid will]] remain. This proofreading mechanism greatly improves[[Protein|protein synthesis]] fidelity so mistakes are less than 1 in 10,000 [[Amino acid|amino acids]] <ref>Berg JM, Tymoczko JL, Stryer L (2007) Biochemistry p864-866, 6th edition, WH Freeman, New York</ref>. | ||
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Revision as of 17:40, 29 November 2010
Aminoacyl tRNA synthetases are enzymes which catalyse tRNA molecules linking to their corresponding amino acid to create aminoacyl tRNAs (or charged tRNAs). They can also be referred to as activating enzymes.
Aminoacylation of tRNAs
tRNA molecules joined to their corresponding amino acid are called aminoacyl tRNAs, this reaction is called aminoacylation and is a 2 step reaction driven by ATP and catalysed by aminoacyl tRNA synthetases. Amino acids are activated by adenylation by reacting with ATP to form aminoacyl adenylate (aminoacyl AMP), a high energy intermediate, and pyrophosphate. The next step is the transfer of the aminoacyl group from aminoacyl adenylate to a tRNA molecule to make an aminoacyl tRNA and release AMP [1].
Aminoacyl tRNA synthetases
Aminoacylation must be highly specific as the correct amino acids must be on the correct tRNAs for a functional protein to be synthesised. Aminoacyl tRNA synthetases must be able to distinguish not only between approximately 40 similarly shaped tRNA molecules, but also very similar amino acids acids such as serine, threonine and valine. These enzymes use particular 'identity elements' in different tRNAs, which can be located in the anticodon region, amino acid acceptor stem, variable arm, or a mixture of them. In order to discriminate between different amino acids, aminoacyl tRNA synthetases have a proofreading mechanism. They have an acylation (activation) site and some also have an editing site (not all tRNA synthetases have this, only when the enzyme needs an additional mechanism to distinguish between amino acids). The acylation site rejects amino acids which are too large to fit in the site, and in doing so will accept the correct amino acid, but also other amino acids which are smaller than the correct one. Amino acids which fit into the editing site are hydrolytically cleaved as they are identified as being smaller than the correct amino acid, so only the correct amino acid will remain. This proofreading mechanism greatly improvesprotein synthesis fidelity so mistakes are less than 1 in 10,000 amino acids [2].