Sandbox Reserved 192: Difference between revisions
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=='''Structure'''== | =='''Structure'''== | ||
RNase A is made up of a single polypeptide chain of 124 residues. Of the 20 natural amino acids, RNase A possesses 19 of them, excluding tryptophan. This single polypeptide chain is cross-linked internally by four <scene name='Sandbox_Reserved_192/Disulfide_linkages/4'>disulfide linkages</scene>, which contribute to the stability of RNase A. Long four-stranded anti-parallel <scene name='Sandbox_Reserved_192/Beta_sheet/4'>ß-sheets</scene> and three short <scene name='Sandbox_Reserved_192/Alpha_helices/2'>α-helices</scene> make up the <scene name='Sandbox_Reserved_192/Secondary_structure/3'>secondary structure</scene> of RNase A. The structure of RNase A is often described as kidney shaped, with the active-site residues located within the cleft. <scene name='Sandbox_Reserved_192/Catalytic_residues/2'>His12, Lys41, and His119</scene> residues aid in catalysis. <scene name='Sandbox_Reserved_192/Lysine_41/3'>Lys41</scene> stabilizes the negative charge in the transition state, while <scene name='Sandbox_Reserved_192/His_12/3'>His12</scene> acts as a base and <scene name='Sandbox_Reserved_192/Histidine_119/2'>His119</scene> acts as an acid in catalysis. The amino acid sequence | RNase A is made up of a single polypeptide chain of 124 residues. Of the 20 natural amino acids, RNase A possesses 19 of them, excluding tryptophan. This single polypeptide chain is cross-linked internally by four <scene name='Sandbox_Reserved_192/Disulfide_linkages/4'>disulfide linkages</scene>, which contribute to the stability of RNase A. Long four-stranded anti-parallel <scene name='Sandbox_Reserved_192/Beta_sheet/4'>ß-sheets</scene> and three short <scene name='Sandbox_Reserved_192/Alpha_helices/2'>α-helices</scene> make up the <scene name='Sandbox_Reserved_192/Secondary_structure/3'>secondary structure</scene> of RNase A. The structure of RNase A is often described as kidney shaped, with the active-site residues located within the cleft. <scene name='Sandbox_Reserved_192/Catalytic_residues/2'>His12, Lys41, and His119</scene> residues aid in catalysis. <scene name='Sandbox_Reserved_192/Lysine_41/3'>Lys41</scene> stabilizes the negative charge in the transition state, while <scene name='Sandbox_Reserved_192/His_12/3'>His12</scene> acts as a base and <scene name='Sandbox_Reserved_192/Histidine_119/2'>His119</scene> acts as an acid in catalysis. | ||
The amino acid sequence was found to determine the three-dimensional structure of RNase A by Christian Anfinsen in the 1950s. Urea was used to denature RNase A, and mercaptoethanol was used to reduce and cleave the four disulfide bonds in RNase A to yield eight Cys residues. When the urea and mercaptoethanol were removed, the denatured ribonuclease refolded spontaneously into its correct tertiary structure, with restoration of its catalytic activity. Disulfide bonds were also reformed in the same position. The Anfinsen experiment provided evidence that the amino acid sequence contained all the information required for the protein to fold into its native three-dimensional structure. | |||
=='''History'''== | =='''History'''== | ||