Isochorismate pyruvate lyase: Difference between revisions
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==Function== | ==Function== | ||
[[Image:superposition of open and closed.png|300px|right]] | |||
It is involved in the catalysis of the transformation of isochorismate to pyruvate and salicylate. This reaction is the committed step in the biosynthesis of salicylate-based siderophores in several pathogenic bacteria. In plants, salicylate produced from isochorismate is important for the plant defense mechanisms known as local and systemic acquired resistance It has also been found to have secondary activity of catalyzing the transformation of chorismate to prephenate (chorismate mutase activity), although this is weak. The physiological role of IPL or PchB uses a pericyclic hydrogen transfer mechanism to produce salicylate from isochorismate as opposed to the notion that general base or acid catalysis would occur. This property resembles chorismate mutase enzyme that catalyze pericyclic reactions. IPL is a structural homolog of chorismate mutase despite very low sequence identity (approx 20%). The similarity is restricted to the active sites which are conserved (Annu. Rev. Biophys. 2008. 37:153–73) and it has been found that chorismate mutase cannot be mutated to acquire IPL activity. IPL has been considered for improvement of its secondary activity computationally using hybrid quantum mechanics/ Molecular mechanics (J. AM. CHEM. SOC. 2008, 130, 2894-2895).Homologous genes are found in other microorganisms. It is also involved in bacterial siderophore synthesis. | It is involved in the catalysis of the transformation of isochorismate to pyruvate and salicylate. This reaction is the committed step in the biosynthesis of salicylate-based siderophores in several pathogenic bacteria. In plants, salicylate produced from isochorismate is important for the plant defense mechanisms known as local and systemic acquired resistance It has also been found to have secondary activity of catalyzing the transformation of chorismate to prephenate (chorismate mutase activity), although this is weak. The physiological role of IPL or PchB uses a pericyclic hydrogen transfer mechanism to produce salicylate from isochorismate as opposed to the notion that general base or acid catalysis would occur. This property resembles chorismate mutase enzyme that catalyze pericyclic reactions. IPL is a structural homolog of chorismate mutase despite very low sequence identity (approx 20%). The similarity is restricted to the active sites which are conserved (Annu. Rev. Biophys. 2008. 37:153–73) and it has been found that chorismate mutase cannot be mutated to acquire IPL activity. IPL has been considered for improvement of its secondary activity computationally using hybrid quantum mechanics/ Molecular mechanics (J. AM. CHEM. SOC. 2008, 130, 2894-2895).Homologous genes are found in other microorganisms. It is also involved in bacterial siderophore synthesis. | ||
Peter Kast et al, propose for PchB a rare [1,5]-sigmatropic reaction mechanism that invokes electrostatic catalysis in analogy to the [3,3]-pericyclic rearrangement of chorismate in Chorismate mutases (CM). | Peter Kast et al, propose for PchB a rare [1,5]-sigmatropic reaction mechanism that invokes electrostatic catalysis in analogy to the [3,3]-pericyclic rearrangement of chorismate in Chorismate mutases (CM). | ||
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[[Image:nativeopen.png|300px|left]][[Image:closed.png|300px|left]][[Image:open.png|300px|left]] | [[Image:nativeopen.png|300px|left]][[Image:closed.png|300px|left]][[Image:open.png|300px|left]] | ||
This is a 101-residue chain made of three alpha helices. It is found in the apo form, pyruvate bound open anf pyruvate bound closed forms.Some of the regions overlap with the regions of RdgC base domain which is a DNA binding recombination association protein.The quaternary structure of PchB was found to be dimeric as it is for EcCM (the homologous Chorismate Mutase), and most catalytic residues in the active site of EcCM are conserved in PchB. Moreover, it was shown that pchB complements the CM deficiency of an ''E. coli'' mutant strain and that PchB has low CM activity ''in vitro''. | This is a 101-residue chain made of three alpha helices. It is found in the apo form, pyruvate bound open anf pyruvate bound closed forms.Some of the regions overlap with the regions of RdgC base domain which is a DNA binding recombination association protein.The quaternary structure of PchB was found to be dimeric as it is for EcCM (the homologous Chorismate Mutase), and most catalytic residues in the active site of EcCM are conserved in PchB. Moreover, it was shown that pchB complements the CM deficiency of an ''E. coli'' mutant strain and that PchB has low CM activity ''in vitro''. | ||
[[Image:1ecms.png|300px|right]] | |||
==Chemistry== | ==Chemistry== | ||
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==Conserved Residues== | ==Conserved Residues== | ||
5 amino acids that are conserved in the homologous protein 1ECM, which is a chorismate mutase are Arg14, Arg 31, Lys 42(disordered in the open structure), Arg 53 and Gln 90. There are 3 other residues that are not conserved in pchB, however (Tyr 86, Ala 50 and Val 54). | 5 amino acids that are conserved in the homologous protein 1ECM, which is a chorismate mutase are Arg14, Arg 31, Lys 42(disordered in the open structure), Arg 53 and Gln 90. There are 3 other residues that are not conserved in pchB, however (Tyr 86, Ala 50 and Val 54). | ||
[[Image:i87.png|300px|right]] | |||
[[Image:native open.png|300px|left]] | [[Image:native open.png|300px|left]] | ||