Intrinsically Disordered Protein: Difference between revisions
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Christian B. Anfinsen and coworkers. In the 1960's, they showed that RNAse, when denatured so that 99% of its enzymatic activity was lost, could regain enzymatic activity within seconds when the denaturing agent was removed under proper conditions<ref>For the sake of brevity, this description is oversimplified. RNAse needed to be reduced to break disulfide bonds, as well as using 8 M urea, for denaturation. Oxidation without the denaturant then left an inactive enzyme because the disulfide bonds formed randomly, precluding proper folding except very slowly (many hours). Only when protein disulfide isomerase was added did the re-folding occur at a physiological rate (about a minute). The fact that RNAse could thus be trapped in an inactive conformation under physiological conditions contributed to the insights developed by Anfinsen and his team. Proteins lacking disulfides renatured in seconds. For details, see [http://nobelprize.org/nobel_prizes/chemistry/laureates/1972/anfinsen-lecture.html Anfinsen's Nobel Lecture.]</ref>. They concluded that the amino acid sequence is sufficient for a protein to fold into its functional, lowest energy conformation. This work won the [[Nobel_Prizes_for_3D_Molecular_Structure|1972 Nobel Prize]], and was subsequently confirmed and extended by many researchers. | Christian B. Anfinsen and coworkers. In the 1960's, they showed that RNAse, when denatured so that 99% of its enzymatic activity was lost, could regain enzymatic activity within seconds when the denaturing agent was removed under proper conditions<ref>For the sake of brevity, this description is oversimplified. RNAse needed to be reduced to break disulfide bonds, as well as using 8 M urea, for denaturation. Oxidation without the denaturant then left an inactive enzyme because the disulfide bonds formed randomly, precluding proper folding except very slowly (many hours). Only when protein disulfide isomerase was added did the re-folding occur at a physiological rate (about a minute). The fact that RNAse could thus be trapped in an inactive conformation under physiological conditions contributed to the insights developed by Anfinsen and his team. Proteins lacking disulfides renatured in seconds. For details, see [http://nobelprize.org/nobel_prizes/chemistry/laureates/1972/anfinsen-lecture.html Anfinsen's Nobel Lecture.]</ref>. They concluded that the amino acid sequence is sufficient for a protein to fold into its functional, lowest energy conformation. This work won the [[Nobel_Prizes_for_3D_Molecular_Structure|1972 Nobel Prize]], and was subsequently confirmed and extended by many researchers. | ||
Recently, it has been recognized that not all proteins function in a folded state<ref>PMID: 10550212</ref><ref>PMID: 11381529</ref><ref>PMID: 11784292</ref><ref name="tompa2002">PMID: 12368089</ref><ref>Summary of the previous paper (Tompa, 2002): The disorder of intrinsically unstructured proteins (IUP's) is crucial to their functions. They may adopt defined but extended structures when bound to cognate ligands. Their amino acid compositions are less hydrophobic than those of soluble proteins. They lack hydrophobic cores, and hence do not become insoluble when heated. About 40% of eukaryotic proteins have at least one long (>50 residues) disordered region. Roughly 10% of proteins in various genomes have been predicted to be fully disordered. Presently over 100 IUP's have been identified; none are enzymes. Obviously, IUP's are greatly underrepresented in the Protein Data Bank, although there are a few cases of an IUP bound to a folded (intrinsically structured) protein. Here, Tompa suggests five functional categories for intrinsically unstructured proteins and domains: entropic chains (bristles to ensure spacing, springs, flexible spacers/linkers), effectors (inhibitors and disassemblers), scavengers, assemblers, and display sites. (Summary by Eric Martz.)</ref><ref>PMID: 18952168</ref>. Some proteins must be unfolded or disordered in order to perform their functions, and others fold only in complex with target structures<ref name="gunasekaran2003">PMID: 12575995</ref><ref>Summary of the previous paper (Gunasekaran ''et al.'', 2003): Argues that proteins involved in extensive protein-protein interactions can function effectively despite having their structure depend upon such interactions, so that as monomers they are natively disordered. Dispensing with the structural framework (scaffold) needed to maintain a stable fold in the monomer increases efficiency by reducing size. This may account for the large percentage (roughly half) of all proteins that are predicted to be natively disordered. (Summary by Eric Martz.)</ref><ref>PMID: 15738986</ref>. These are termed '''intrinsically disordered protein (IDP), intrinsically unstructured protein (IUP), or natively unfolded protein'''. | Recently, it has been recognized that not all proteins function in a folded state<ref>PMID: 10550212</ref><ref>PMID: 11381529</ref><ref>PMID: 11784292</ref><ref name="tompa2002">PMID: 12368089</ref><ref>Summary of the previous paper (Tompa, 2002): The disorder of intrinsically unstructured proteins (IUP's) is crucial to their functions. They may adopt defined but extended structures when bound to cognate ligands. Their amino acid compositions are less hydrophobic than those of soluble proteins. They lack hydrophobic cores, and hence do not become insoluble when heated. About 40% of eukaryotic proteins have at least one long (>50 residues) disordered region. Roughly 10% of proteins in various genomes have been predicted to be fully disordered. Presently over 100 IUP's have been identified; none are enzymes. Obviously, IUP's are greatly underrepresented in the Protein Data Bank, although there are a few cases of an IUP bound to a folded (intrinsically structured) protein. Here, Tompa suggests five functional categories for intrinsically unstructured proteins and domains: entropic chains (bristles to ensure spacing, springs, flexible spacers/linkers), effectors (inhibitors and disassemblers), scavengers, assemblers, and display sites. (Summary by Eric Martz.)</ref><ref>PMID: 18952168</ref><ref>PMID: 15284216</ref>. Some proteins must be unfolded or disordered in order to perform their functions, and others fold only in complex with target structures<ref name="gunasekaran2003">PMID: 12575995</ref><ref>Summary of the previous paper (Gunasekaran ''et al.'', 2003): Argues that proteins involved in extensive protein-protein interactions can function effectively despite having their structure depend upon such interactions, so that as monomers they are natively disordered. Dispensing with the structural framework (scaffold) needed to maintain a stable fold in the monomer increases efficiency by reducing size. This may account for the large percentage (roughly half) of all proteins that are predicted to be natively disordered. (Summary by Eric Martz.)</ref><ref>PMID: 15738986</ref>. These are termed '''intrinsically disordered protein (IDP), intrinsically unstructured protein (IUP), or natively unfolded protein'''. | ||
By some estimates, about 10% of all proteins are fully disordered, and about 40% of eukaryotic proteins have at least one long (>50 amino acids) disordered loop<ref name="tompa2002" />. Such sequences, under physiological conditions ''in vitro'', display physicochemical characteristics resembling those of random coils. They possess little or no ordered structure, having instead an extended conformation with high intra-molecular flexibility, lacking any tightly packed core. | By some estimates, about 10% of all proteins are fully disordered, and about 40% of eukaryotic proteins have at least one long (>50 amino acids) disordered loop<ref name="tompa2002" />. Such sequences, under physiological conditions ''in vitro'', display physicochemical characteristics resembling those of random coils. They possess little or no ordered structure, having instead an extended conformation with high intra-molecular flexibility, lacking any tightly packed core. | ||
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Many [[X-ray crystallography|crystallographic]] structures have missing loops -- that is, ranges of amino acids with no [[atomic coordinate file|atomic coordinates]] in the model. These "gaps" in the model are often thought to be artifacts of inadvertant disorder in the crystal. In some cases, these gaps may be alerting us to the presence of intrinsically disordered loops in an otherwise folded protein. Such gaps are the basis for the [[#Protein disorder predictors|DISOPRED2 disorder prediction server]]. [[FirstGlance in Jmol]] offers [[Temperature_value#Missing_Residues|one method for locating and visualizaing such gaps]]. | Many [[X-ray crystallography|crystallographic]] structures have missing loops -- that is, ranges of amino acids with no [[atomic coordinate file|atomic coordinates]] in the model. These "gaps" in the model are often thought to be artifacts of inadvertant disorder in the crystal. In some cases, these gaps may be alerting us to the presence of intrinsically disordered loops in an otherwise folded protein. Such gaps are the basis for the [[#Protein disorder predictors|DISOPRED2 disorder prediction server]]. [[FirstGlance in Jmol]] offers [[Temperature_value#Missing_Residues|one method for locating and visualizaing such gaps]]. | ||
Despite the existence of compelling evidence for IUPs and intrinsically disordered loops beginning in 1990<ref name="struhl1990" /><ref>PMID: 2236048</ref>, many current textbooks of biochemistry and even some monographs on protein structure fail to mention intrinsic disorder and its importance for protein function<ref>PMID: 18831774</ref><ref>Martz, E. Book review of <i>Introduction to protein science—architecture, function, and genomics: Lesk, Arthur M.</i>. <i>Biochem. Mol. Biol. Educ.</i> 33:144-5 (2006). [http://dx.doi.org/10.1002/bmb.2005.494033022442 DOI: 10.1002/bmb.2005.494033022442]</ref>. In 2011, Chouard provided a readable and informative overview of IUPs and how some of them function<ref>PMID: 21390105</ref>. | Despite the existence of compelling evidence for IUPs and intrinsically disordered loops beginning in 1990<ref name="struhl1990" /><ref>PMID: 2236048</ref><ref>For the ''unstructured domain'' interpretation of Pontius' early work, see the 2004 review by Tompa and Csermley, PMID: 15284216</ref>, many current textbooks of biochemistry and even some monographs on protein structure fail to mention intrinsic disorder and its importance for protein function<ref>PMID: 18831774</ref><ref>Martz, E. Book review of <i>Introduction to protein science—architecture, function, and genomics: Lesk, Arthur M.</i>. <i>Biochem. Mol. Biol. Educ.</i> 33:144-5 (2006). [http://dx.doi.org/10.1002/bmb.2005.494033022442 DOI: 10.1002/bmb.2005.494033022442]</ref>. In 2011, Chouard provided a readable and informative overview of IUPs and how some of them function<ref>PMID: 21390105</ref>. | ||
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