the enzyme belongs to the 5-hydroxyisourate hydrolase/transthyretin superfamily: evolutionary and functional analyses, overview. Teleosts have highly diverged genomes that resulted from whole genome duplication, which leads to an extensive diversity of paralogous genes. Transthyretin, an extracellular thyroid hormone binding protein, is thought to have evolved from an ancestral 5-hydroxyisourate hydrolase by gene duplication at some stage of chordate evolution. Phylogenetic analysis of the teleost aa sequences reveals the presence of two HIUHase subfamilies, HIUHase 1 (which has an N-terminal peroxisomal targeting signal-2) and HIUHase 2 (which does not have an N-terminal PTS2), and one transthyretin family
point mutation Y98Cin the gene encoding mouse HIU hydrolase, Urah, results in undetectable protein expression. Mice homozygous for this mutation develop elevated platelet counts secondary to excess thrombopoietin production and hepatomegaly. The majority of homozygous mutant mice also develop hepatocellular carcinoma, and tumor development is accelerated by exposure to radiation
reaction is likely to be initiated by a water molecule that is first activated by deprotonation. The hydrogen-bonding interactions between the water molecule and residues His7 and His92 would serve to orient the water ideally for attack at C6 of the purine ring. The C-terminal serine residue, Ser108, is in position to form a hydrogen bond to His7 and may indirectly participate in catalysis by inductively activating this residue. Deprotonation of the water by His7 creates a hydroxide nucleophile that attacks C6 of the purine ring, leading to a tetrahedral oxyanion intermediate. The charge on the resulting oxyanion would be stabilized by the positively charged guanidinium group of Arg41. Arg41 from the neighboring chain helps to stabilize the charge on the oxyanion intermediate.Collapse of the oxyanion would then lead to ring opening, with the final proton coming from the nearby Arg41. The original proton abstracted from a water molecule by His7 would then be transferred to Arg41 to complete the catalytic cycle
reaction is likely to be initiated by a water molecule that is first activated by deprotonation. The hydrogen-bonding interactions between the water molecule and residues His7 and His92 would serve to orient the water ideally for attack at C6 of the purine ring. The C-terminal serine residue, Ser108, is in position to form a hydrogen bond to His7 and may indirectly participate in catalysis by inductively activating this residue. Deprotonation of the water by His7 creates a hydroxide nucleophile that attacks C6 of the purine ring, leading to a tetrahedral oxyanion intermediate. The charge on the resulting oxyanion would be stabilized by the positively charged guanidinium group of Arg41. Arg41 from the neighboring chain helps to stabilize the charge on the oxyanion intermediate.Collapse of the oxyanion would then lead to ring opening, with the final proton coming from the nearby Arg41. The original proton abstracted from a water molecule by His7 would then be transferred to Arg41 to complete the catalytic cycle
reaction is likely to be initiated by a water molecule that is first activated by deprotonation. The hydrogen-bonding interactions between the water molecule and residues His7 and His92 would serve to orient the water ideally for attack at C6 of the purine ring. The C-terminal serine residue, Ser108, is in position to form a hydrogen bond to His7 and may indirectly participate in catalysis by inductively activating this residue. Deprotonation of the water by His7 creates a hydroxide nucleophile that attacks C6 of the purine ring, leading to a tetrahedral oxyanion intermediate. The charge on the resulting oxyanion would be stabilized by the positively charged guanidinium group of Arg41. Arg41 from the neighboring chain helps to stabilize the charge on the oxyanion intermediate.Collapse of the oxyanion would then lead to ring opening, with the final proton coming from the nearby Arg41. The original proton abstracted from a water molecule by His7 would then be transferred to Arg41 to complete the catalytic cycle
mutants Y116T, I16A/Y116T and mutant I16A/Y116T in complex with thyroxine, to 1.7 A, 2.3 A., and 1.95 A resoultion. Structural comparison of HIUase and transthyretin, TTR. Mutations Y116T and I16A are likely to be crucial events in order to induce, after a gene duplication event, the conversion of the enzyme HIUase into a binding protein, transthyretin. The mutations at the active sites of HIUase open up the two ends of the channel that transverses the entire tetrameric protein, generating two cavities accessible to the thyroxine molecule and abrogating, at the same time, the enzymatic activity
to 1.8 A resolution, and modeling of substrate 5-hydroxyisourate into the active site. The four chains of the enzyme come together to form a homotetramer with 222 symmetry. The tetramer is a dimer of dimers, with two protomers arranged to create an extended beta-sheet that makes up the dimerdimer interface
mutation at the active sites of HIUase, opens up one end of the channel that transverses the entire tetrameric protein, generating a cavity accessible to the thyroxine molecule and abrogating, at the same time, the enzymatic activity
mutations at the active sites of HIUase open up the two ends of the channel that transverses the entire tetrameric protein, generating two cavities accessible to the thyroxine molecule and abrogating, at the same time, the enzymatic activity
mutation at the active sites of HIUase, opens up one end of the channel that transverses the entire tetrameric protein, generating a cavity accessible to the thyroxine molecule and abrogating, at the same time, the enzymatic activity
point mutation in the gene encoding mouse HIU hydrolase, Urah, that perturbes uric acid metabolism within the liver. The substitution of cysteine for tyrosine in a conserved helical region results in undetectable protein expression. Mice homozygous for this mutation develop elevated platelet counts secondary to excess thrombopoietin production and hepatomegaly. The majority of homozygous mutant mice also develop hepatocellular carcinoma, and tumor development is accelerated by exposure to radiation
point mutation Y98Cin the gene encoding mouse HIU hydrolase, Urah, results in undetectable protein expression. Mice homozygous for this mutation develop elevated platelet counts secondary to excess thrombopoietin production and hepatomegaly. The majority of homozygous mutant mice also develop hepatocellular carcinoma, and tumor development is accelerated by exposure to radiation