Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The molecular detection of heterozygotes for hyperphenylalaninemia is difficult due to the large number of mutations in the PAH gene. For this reason, various indexes that measure plasma concentrations of phenylalanine (Phe) and tyrosine (Tyr), as an expression of Phe metabolizing capacity, have been used for the detection of carriers for mutations in the PAH gene. In this study, we contrast the biochemical and the molecular data in order to know if this is an accurate method. Familial genetic analysis of the PAH gene in 93 parents of hyperphenylalaninemia patients allows the study of the biochemical expression of the different mutant alleles. Molecular study was performed by SSCP and DGGE analyses of PAH genes, and plasma amino acid analysis by ion-exchange chromatography. Then the biochemical and molecular data were compared by the Student t test. The results found show a relationship between the severity of PKU/HPA mutations in the PAH gene and their biochemical phenotype (Phe/Tyr, Phe2/Tyr) as an expression of the residual enzymatic activity. The study adds further information about the prevalent Mediterranean allele mutations.
Mol Genet Metab 1999 Jun
PMID:Biochemical phenotype and its relationship with genotype in hyperphenylalaninemia heterozygotes. 1035 15

Phenylalanine hydroxylase (PAH) is the key enzyme in phenylalanine metabolism. PAH deficiency results in hyperphenylalaninemia, leading to severe mental retardation in the classical form of the disease, phenylketonuria (PKU). Previously the expression of PAH could only unambiguously be demonstrated in human liver, whereas in rodents PAH expression has been established in kidney and liver. Reports concerning PAH activity in other human or rodent tissues were severely questioned by subsequent investigations such that they did not gain general recognition. Conducting Northern blot analyses, we detected the PAH transcript in RNA isolated from human liver, kidney, pancreas, and brain. PAH gene expression in human kidney was subsequently investigated by RNase protection assay analyses, RNA in situ hybridization, immunohistochemistry, enzyme assay, and cDNA isolation. These experiments allowed the conclusive verification of a functional PAH enzyme in human kidney. The primary structure of the kidney transcript corresponded to the structure of the liver transcript. Human kidney PAH may play a significant role in phenylalanine homeostasis of the organism, as impaired phenylalanine hydroxylation has been observed in renal failure and differences in the regulation of the kidney versus the liver enzyme have been indicated. These results provide new aspects to research into the basis for the heterogeneity of hyperphenylalaninemia phenotypes and establish that the expression of the human PAH gene is not limited to the liver.
Mol Genet Metab 1999 Aug
PMID:Human phenylalanine hydroxylase gene expression in kidney and other nonhepatic tissues. 1044 41

Phenylketonuria and mild hyperphenylalaninemias are allelic disorders caused by mutations in the phenylalanine hydroxylase (PAH) gene. Following identification of the disease-causing mutation in 11 PAH-deficient patients, we tested the activity of the mutant gene products in an eukaryotic expression system. Two mutations markedly reduced PAH activity (A259V and L333F), one mutation mildly altered the enzyme activity (E390G), while the majority of mutant genotypes reduced the in vitro expression of PAH activity to 15-30% of controls. Comparing the predicted residual activity derived from expression studies to the clinical phenotypes of our PAH-deficient patients, we found that homozygosity for the L333F and E390G mutations resulted in severe and mild PAH deficiencies, respectively, both in vivo and in vitro, while compound heterozygosity (L333F/E390G) resulted in an intermediate dietary tolerance. Similarly, in vitro expression studies largely predicted dietary tolerance in compound heterozygotes for the A259V/IVS12nt1 (typical PKU), A259V/A403V, G218V/I65T, and G218V/R158Q mutations (mild variants). Taken together, these results support the view that expression studies are useful in predicting residual enzyme activity and that the mutant genotype at the PAH locus is the major determinant of metabolic phenotype in hyperphenylalaninemias.
Mol Genet Metab 1999 Sep
PMID:The mutant genotype is the main determinant of the metabolic phenotype in phenylalanine hydroxylase deficiency. 1047 81

The human phenylalanine hydroxylase gene (PAH) (locus on human chromosome 12q24.1) contains the expressed nucleotide sequence which encodes the hepatic enzyme phenylalanine hydroxylase (PheOH). The PheOH enzyme hydroxylates the essential amino acid l-phenylalanine resulting in another amino acid, tyrosine. This is the major pathway for catabolizing dietary l-phenylalanine and accounts for approximately 75% of the disposal of this amino acid. The autosomal recessive disease phenylketonuria (PKU) is the result of a deficiency of PheOH enzymatic activity due to mutations in the PAH gene. Of the mutant alleles that cause hyperphenylalaninemia or PKU 99% map to the PAH gene. The remaining 1% maps to several genes that encode enzymes involved in the biosynthesis or regeneration of the cofactor ((6R)-l-erythro-5,6,7,8-tetrahydrobiopterin) regenerating the cofactor (tetrahydrobiopterin) necessary for the hydroxylation reaction. The recently solved crystal structures of human phenylalanine hydroxylase provide a structural scaffold for explaining the effects of some of the mutations in the PAH gene and suggest future biochemical studies that may increase our understanding of the PKU mutations.
Mol Genet Metab 1999 Oct
PMID:The structural basis of phenylketonuria. 1052 63

Mutations in the arylsulfatase E gene, located on the X chromosome, have been shown to cause chondrodysplasia punctata (CDP). A substitution of arginine with serine at amino acid 12 (R12S) was identified in a patient with typical features of mild symmetrical CDP including mild mental retardation. The proband was institutionalized and was found to have seven full and half siblings all of whom were microcephalic. Six siblings are alive and all are mentally retarded. The mother is borderline retarded. The mother and three daughters are carriers of the R12S change, but do not appear to have CDP. A son and three other daughters do not carry the R12S change. Further studies revealed that the mother had phenylketonuria (PKU) and the children maternal PKU. This suggests that the R12S change is not the primary cause of short stature, microcephaly, and mental retardation in this family. The relationship between CDP and PKU, both of which can cause short statue and mental retardation, is discussed.
Mol Genet Metab 1999 Dec
PMID:Late diagnosis of maternal PKU in a family segregating an arylsulfatase [corrected] E mutation causing symmetrical chondrodysplasia punctata. 1060 80

Phenylalanine hydroxylase (PAH) is a tetrahydrobiopterin and non-heme iron-dependent enzyme that hydroxylates L-Phe to l-Tyr using molecular oxygen as additional substrate. A dysfunction of this enzyme leads to phenylketonuria (PKU). The conformation and distances to the catalytic iron of both L-Phe and the cofactor analogue L-erythro-7,8-dihydrobiopterin (BH2) simultaneously bound to recombinant human PAH have been estimated by (1)H NMR. The resulting bound conformers of both ligands have been fitted into the crystal structure of the catalytic domain by molecular docking. In the docked structure L-Phe binds to the enzyme through interactions with Arg270, Ser349 and Trp326. The mode of coordination of Glu330 to the iron moiety seems to determine the amino acid substrate specificity in PAH and in the homologous enzyme tyrosine hydroxylase. The pterin ring of BH2 pi-stacks with Phe254, and the N3 and the amine group at C2 hydrogen bond with the carboxylic group of Glu286. The ring also establishes specific contacts with His264 and Leu249. The distance between the O4 atom of BH2 and the iron (2.6(+/-0.3) A) is compatible with coordination, a finding that is important for the understanding of the mechanism of the enzyme. The hydroxyl groups in the side-chain at C6 hydrogen bond with the carbonyl group of Ala322 and the hydroxyl group of Ser251, an interaction that seems to have implications for the regulation of the enzyme by substrate and cofactor. Some frequent mutations causing PKU are located at residues involved in substrate and cofactor binding. The sites for hydroxylation, C4 in L-Phe and C4a in the pterin are located at a distance of 4.2 and 4.3 A from the iron moiety, respectively, and at 6.3 A from each other. These distances are adequate for the intercalation of iron-coordinated molecular oxygen, in agreement with a mechanistic role of the iron moiety both in the binding and activation of dioxygen and in the hydroxylation reaction.
J Mol Biol 1999 Dec 03
PMID:The structural basis of the recognition of phenylalanine and pterin cofactors by phenylalanine hydroxylase: implications for the catalytic mechanism. 1061 Jul 98

Missense mutations account for 48% of all reported human disease-causing alleles. Since few are predicted to ablate directly an enzyme's catalytic site or other functionally important amino acid residues, how do most missense mutations cause loss of function and lead to disease? The classic monogenic phenotype hyperphenylalaninemia (HPA), manifesting notably as phenylketonuria (PKU), where missense mutations in the PAH gene compose 60% of the alleles impairing phenylalanine hydroxylase (PAH) function, allows us to examine this question. Here we characterize four PKU-associated PAH mutations (F39L, K42I, L48S, I65T), each changing an amino acid distant from the enzyme active site. Using three complementary in vitro protein expression systems, and 3D-structural localization, we demonstrate a common mechanism. PAH protein folding is affected, causing altered oligomerization and accelerated proteolytic degradation, leading to reduced cellular levels of this cytosolic protein. Enzyme specific activity and kinetic properties are not adversely affected, implying that the only way these mutations reduce enzyme activity within cells in vivo is by producing structural changes which provoke the cell to destroy the aberrant protein. The F39L, L48S, and I65T PAH mutations were selected because each is associated with a spectrum of in vivo HPA among patients. Our in vitro data suggest that interindividual differences in cellular handling of the mutant, but active, PAH proteins will contribute to the observed variability of phenotypic severity. PKU thus supports a newly emerging paradigm both for mechanism whereby missense mutations cause genetic disease and for potential modulation of a disease phenotype.
Mol Genet Metab 2000 Feb
PMID:Characterization of phenylketonuria missense substitutions, distant from the phenylalanine hydroxylase active site, illustrates a paradigm for mechanism and potential modulation of phenotype. 1072 Apr 36

The molecular mechanism underlying the metabolic defect in phenylketonuria (PKU) patients carrying the V388M missense mutation of the phenylalanine hydroxylase (PAH) gene has been characterized. An in vitro prokaryotic expression system has been used to produce both the wild-type and the mutant form of the human PAH (hPAH) protein. The recombinant enzymes, obtained as fusion proteins, were purified by immobilized metal affinity chromatography and recovered in high yields. The wild-type hPAH possessed a high specific activity and its kinetic properties were the same as those reported for the enzyme isolated from human liver and other recombinant wild-type hPAH enzymes. The recombinant V388M mutant form exhibited a reduced specific activity equivalent to 30% of the wild-type hPAH enzyme when assayed using the synthetic cofactor (6-methyltetrahydropterin). Lower values were obtained (23 and 19%) when the mutant enzyme was assayed with the natural cofactor ((6R)-tetrahydrobiopterin) and different concentrations of l-phenylalanine. The enzyme kinetic studies of the V388M mutant protein revealed that this enzyme was a kinetic variant form of hPAH with a reduced affinity for l-phenylalanine and for the natural cofactor ((6R)-tetrahydrobiopterin). The residual activities determined for the V388M form of hPAH were compatible with the phenotype presented by the PKU patients harboring the V388M mutation in the PAH gene.
Mol Genet Metab 2000 Mar
PMID:The V388M mutation results in a kinetic variant form of phenylalanine hydroxylase. 1076 75

It has been postulated that the significant incidence of learning disabilities in well-treated patients with phenylketonuria (PKU) may be due, in part, to reduced production of neurotransmitters as a result of deficient tyrosine transport across the neuronal cell membrane. Hypotyrosinemia has been reported in treated and untreated PKU but virtually no data are available. We decided to examine this in our patient population and to compare it with the published norms, patient data from our hospital clinical biochemical laboratory database, and a group of normal children and adolescents in a private pediatric practice. We found that the mean nonfasting plasma tyrosine in 99 classical PKU patients was 41.1 micromol/L, in 26 mild (atypical) PKU patients 53.3 micromol/L, and in 35 non-PKU mild hyperphenylalaninemia patients 66.6 micromol/L. This compared to nonfasting plasma tyrosine levels in 102 non-PKU subjects of 64.0 micromol/L in our hospital biochemistry database, 69.1 micromol/L in 58 volunteers in the private office practice, and 64-78.8 micromol/L in infants, children, and adolescents in the literature review. Our data support the previously undocumented statements in the literature that plasma tyrosine levels are low in PKU.
Mol Genet Metab 2000 Apr
PMID:"Hypotyrosinemia" in phenylketonuria. 1087 Aug 46

Maternal phenylketonuria (PKU) syndrome results in multiple congenital anomalies in the offspring, usually consisting of microcephaly, intrauterine growth retardation, dysmorphology, and congenital heart disease. Pregnancies treated preconceptionally with a phenylalanine-restricted diet and control of maternal blood phenylalanine levels within the recommended range result in normal offspring. However, in this 15-year study, several significant factors resulted in microcephaly in 27% of the offspring, and 7% exhibited serious congenital heart disease. These results occurred chiefly in women with mean IQ scores of 83 associated with low socioeconomic status and decreased educational achievement. Another important factor associated with suboptimal control of blood phenylalanine levels during pregnancy was the fact that most pregnancies were not carefully planned and occurred in women off dietary treatment with phenylalanine-restricted products. These results indicate that greater effort must be developed to assist women with PKU in remaining on diet during their reproductive years. It appears that continued adherence to the diet, resulting in normal maternal intelligence, is an important contribution to improved fetal development.
Mol Genet Metab
PMID:Maternal phenylketonuria: an international study. 1100 15


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>