Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.3.1.108 (TAT)
 2,389 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Thyroxine-binding globulin (TBG) is a liver glycoprotein that transports thyroid hormone in serum. In 1987 a variant TBG was discovered in an infant born in Quebec, following an investigation prompted by the finding of low blood thyroxine (T4) level on screening for neonatal hypothyroidism. This variant, TBG-Quebec, has cathodal shift on isoelectric focusing, reduced affinity for thyroxine, and markedly reduced stability. The latter property of the variant molecule is probably responsible for the partial TBG deficiency. We now report the results of sequencing of the entire coding region and exon-intron junctions of TBG-Quebec, which revealed two nucleotide substitutions; one, located in exon 3, changes the normal codon 283 of TTG (leucine) to that of TTT (phenylalanine), and the other, in exon 4, results in the replacement of the normal histidine-331 (CAT) by tyrosine (TAT). Allele-specific amplification (ASA) confirmed the cosegregation of the two nucleotide substitutions with the TBG-Quebec phenotype in individual members of this family. The substitution in codon 283, but not that in codon 331, has been previously described and, when occurring alone, does not alter the properties of the gene product. Thus, it appears that the replacement of histidine-331 by tyrosine is responsible for the observed altered properties of TBG-Quebec. However, the question of whether substitution of both amino acids is necessary for expression of the variant phenotype has yet to be answered.
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PMID:Sequencing of the variant thyroxine-binding globulin (TBG)-Quebec reveals two nucleotide substitutions. 190 89

Tyrosine aminotransferase (TAT, EC 2.6.1.5) from the kinetoplastid, Crithidia fasciculata, was purified over 2000 fold to electrophoretic homogeneity. The native form of the enzyme had a molecular weight of approximately 100,000, whereas under denaturing conditions it produced two polypeptides of approximately 50,000 and 48,000, respectively. Absence of a reaction with the periodic acid-Schiff stain suggested that the crithidial enzyme was not a glycoprotein. It was relatively stable and remained active over a wide range of pH and temperature. It exhibited a broad substrate specificity and was able to utilize L-tyrosine, L-tryptophan, and L-phenylalanine as amino donors. Antiserum produced against partially purified crithidial tyrosine aminotransferase failed to inhibit the enzymatic activity. The same antiserum cross-reacted with a soluble extract from Trypanosoma brucei gambiense, but not with that from normal mouse liver, confirming evolutionary conservatism between the two protozoa.
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PMID:Purification and characterization of a tyrosine aminotransferase from Crithidia fasciculata. 289 Jan 1

The 130 kd transforming protein of Fujinami sarcoma virus (FSV P130gag -fps) possesses a tyrosine-specific protein kinase activity and is itself phosphorylated at several tyrosine and serine residues in FSV-transformed cells. We have used oligonucleotide-directed mutagenesis of the FSV genome to change the TAT codon for tyrosine (1073), the major site of P130gag -fps phosphorylation, to a TTT codon for phenylalanine that cannot be phosphorylated. This mutant FSV induces the transformation of rat-2 cells but with a long latent period as compared with wild-type FSV. The P130gag -fps protein encoded by the mutant retains the ability to phosphorylate tyrosine, but is five times less active as a kinase in vitro than wild-type FSV P130gag -fps. These data indicate that tyrosine phosphorylation stimulates the biochemical and biological activities of FSV P130gag -fps, and they set a precedent for the ability of this amino acid modification to modulate protein function.
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PMID:Mutagenesis of Fujinami sarcoma virus: evidence that tyrosine phosphorylation of P130gag-fps modulates its biological activity. 632 76

Mouse immunoglobulin heavy-chain variable region (Ig VH) genes apparently arose from the approximately 600-base-pair-long (approximately 12 tandem repeats of the 48-base-pair-long primordial building block sequence TTC-AGC-AGC-CTG-ACT-GGA-TAT-GAC-CTG-GAG-TGG-ACT-TAC-TGC-GCA-AGA) that in the original reading frame specified the amino acid sequence Phe-Ser-Ser-Leu-Thr-Gly-Tyr-Asp-Leu-Glu-Trp-Thr-Tyr-Cys-Ala-Arg. The previously identified, shorter prototype building blocks merely represented particular portions of the above primordial sequence. Even today, the direct descendant in toto of this primordial sequence specifies the last one-sixth of each VH coding sequence: the 83rd to 98th amino acid residues. Furthermore, its four truncated derivatives specify the 4th to 14th, 17th to 23rd, 29th to 37th, and 38th to 48th amino acid residues. Accordingly, all three relatively invariant--therefore, conserved--framework regions (FW-1, FW-2, and FW-3) of VHs are specified by recognizable--therefore, conserved--descendants of the primordial sequence.
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PMID:Identification of the 48-base-long primordial building block sequence of mouse immunoglobulin variable region genes. 680 49

Nature is condemned to play variations of the same theme in evolution, past commitments progressively restricting freedom of choices in evolutionary directions. While each family of genes evolved by the mechanism of gene duplication, this mechanism is extremely inefficient, the usual fate of redundant copies of the ancestral gene being degeneracy. As a result, the euchromatic DNA of higher organisms became a desert in which still-functioning genes are found scattered like oases at an average distance of 35,000 base-pairs of barren stretch between neighbors in the case of mammals. The 20-base-long sequence (AGCTG) (AGCTG) (AGCTG) (GGGTG) can be considered as one of the few ultimate ancestors of all euchromatic DNAs. Long stretches of intergenic spacers are mostly represented by degenerate subfamilies of repeats derived from the above. Certain 30- 50-base-long units of such degenerate subfamilies apparently served as the primordial building block of the ultimate ancestor of each family of genes. For example, the primordial building block of the ancestor for antigen-binding sites (variable regions) of mammalian immunoglobulin heavy chains apparently was TTC-AGC-AGC-CTG-ACT-GGA-TAT GAC-CTG-GAG-TGG-ACT-TAC-TGC-GCA-AGA, which is the original reading frame specified in the 16-amino-acid-residues-long sequence Phe-Ser-Ser-Leu-Thr-Gly-Tyr-Asp-Leu-Glu-Trp-Thr-Tyr-Cys-Ala-Arg.
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PMID:Evolution is condemned to rely upon variations of the same theme: the one ancestral sequence for genes and spacers. 682 Jan 35

One hundred and eighty-one families with multiple endocrine neoplasia type 2A (MEN-2A) or familial medullary thyroid carcinoma (FMTC) have been investigated for mutations in the ret protooncogene in Germany. In 8 families with FMTC or MEN-2A, no mutation could be detected in the cysteine-rich domain encoded in exons 10 and 11 of the ret protooncogene. DNA sequencing of additional exons (no. 13-15) revealed rare noncysteine mutations in 3 families (codons 631, 768, and 844). In contrast to these rare events, heterozygous missense mutations in exon 13, codons 790 and 791, were found in 5 families (4 with MTC only; 1 family with MTC and pheochromocytoma) and 11 patients with apparently sporadic tumors. Two different mutations in codon 790 (TTG-->TTT, TTG-->TTC; Leu790Phe) and one mutation in codon 791 (TAT-->TTT; Tyr791Phe) created a phenylalanine residue. We conclude that codons 790 and 791 of the ret protooncogene represent a new hot spot for FMTC/MEN-2A causing mutations. With the discovery of these considerably common mutations in codons 790 and 791 and the identification of some rare mutations, 100% of the German FMTC/MEN-2A families could be characterized by a mutation in the ret protooncogene.
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PMID:A new hot spot for mutations in the ret protooncogene causing familial medullary thyroid carcinoma and multiple endocrine neoplasia type 2A. 950 24

Although mouse models have been increasingly used for studies of cardiac pathophysiology, there is little information regarding cultured murine cardiac myocytes. Accordingly, we have developed a cell culture model of neonatal mouse cardiac myocytes by modifying a protocol used to prepare neonatal rat myocytes. The principal change is the substitution of cytosine arabinoside for bromodeoxyuridine to prevent fibroblast proliferation. Neonatal murine myocytes exhibited persistent spontaneous contraction and were viable for up to 14 days in culture. By flow cytometry 85% of the cells were cardiac myocytes. In sparse cultures (average cell density 259 cells/mm(2)), both hypoxic preconditioning (n=5) and phenylephrine pretreatment (n=8) produced significant protection of cardiac myocytes from cell death during a prolonged period of severe hypoxia (<0.5% O(2)for 18-20 h, both P<0.05). The phenylephrine effect was inhibited by the alpha(1)-adrenoceptor antagonist prazosin (n=4, P<0.05) and by an xi PKC peptide antagonist (xi V1-2) coupled to a TAT peptide (n=5, P<0. 05). Interestingly, the mixed alpha(1)- and beta -adrenoceptor agonist norepinephrine, which stimulates hypertrophy as measured by(14)[C]phenylalanine incorporation in neonatal rat cardiac myocytes, did not cause hypertrophy in mouse myocytes, suggesting that the signaling pathways for myocardial protection and hypertrophy are likely to be both divergent and species specific. In cardiac myocytes prepared from transgenic mice either homozygous or heterozygous for human Cu/Zn superoxide dismutase, there was protection from cell death (n=3) and restoration of(14)[C]phenyl- alanine uptake (n=4) during prolonged hypoxia (1% O(2)for 3 days, both P<0.05). We conclude that this cellular model, which is relatively simple to prepare, can be used for in-vitro examination of cardiac protection induced by preconditioning agents, various transgenes, and potentially by targeted gene deletions.
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PMID:Neonatal mouse cardiac myocytes exhibit cardioprotection induced by hypoxic and pharmacologic preconditioning and by transgenic overexpression of human Cu/Zn superoxide dismutase. 1101 22

The gene encoding tyrosine aminotransferase (TAT, EC 2.6.1.5) from the parasitic protozoan Trypanosoma cruzi was amplified from genomic DNA, cloned into the pET24a expression vector and functionally expressed as a C-terminally His-tagged protein in Escherichia coli BL21(DE3)pLysS. Purified recombinant TAT exhibited identical electrophoretic and enzymatic properties as the authentic enzyme from T. cruzi. Both recombinant and authentic T. cruzi TATs were highly resistant to limited tryptic cleavage and contained no disulfide bonds. Comprehensive analysis of its substrate specificity demonstrated TAT to be a broad substrate aminotransferase, with leucine, methionine as well as tyrosine, phenylalanine, tryptophan and alanine being utilized efficiently as amino donors. Valine, isoleucine and dicarboxylic amino acids served as poor substrates while polar aliphatic amino acids could not be transaminated. TAT also accepted several 2-oxoacids, including 2-oxoisocaproate and 2-oxomethiobutyrate, in addition to pyruvate, oxaloacetate and 2-oxoglutarate. The functionality of the expression system was confirmed by constructing two variants; one (Arg389) being a completely inactive enzyme; the other (Arg283) retaining its full activity, as predicted from the recently solved three-dimensional structure of T. cruzi TAT. Thus, only one of the two strictly conserved arginines which are essential for the enzymatic activity of subfamily Ialpha aspartate and aromatic aminotransferases is critical for T. cruzi's TAT activity.
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PMID:Recombinant tyrosine aminotransferase from Trypanosoma cruzi: structural characterization and site directed mutagenesis of a broad substrate specificity enzyme. 1129 33

In most circumstances, NF-kappaB, which is essential for osteoclastogenesis, is activated following serine 32/36 phosphorylation of its cytosolic inhibitory protein, IkappaBalpha. In contrast to other cell types, IkappaBalpha, in bone marrow macrophages (BMMs), which are osteoclast precursors, is tyrosine-phosphorylated by c-Src kinase. To address the role of IkappaBalpha phosphorylation in osteoclastogenesis, we generated TAT fusion proteins containing wild-type IkappaBalpha (TAT-WT-IkappaB), IkappaBalpha lacking its NH(2)-terminal 45 amino acids (TAT-IkappaB(46-317)), and IkappaBalpha in which tyrosine residue 42, the c-Src target, is mutated into phenylalanine (TAT-IkappaB(Y42F)). TAT-IkappaB efficiently enters BMMs, and the NF-kappaB-inhibitory protein, once intracellular, is functional. While TAT-WT-IkappaB only slightly inhibits osteoclastogenesis, osteoclast recruitment is diminished >80% by TAT-IkappaB(46-317), an event mirrored by dentin resorption. The fact that TAT alone does not impact osteoclastogenesis, which also resumes following withdrawal of TAT-IkappaB(46-317), establishes that the mutant's anti-osteoclastogenic properties do not reflect toxicity. Affirming a functional role for IkappaB(Tyr(42)) in osteoclastogenesis, TAT-IkappaB(Y42F) is as efficient as TAT-IkappaB(46-317) in blocking osteoclast differentiation. Thus, dominant-negative IkappaBalpha constructs block osteoclastogenesis, and Tyr(42) is essential to the process, increasing the possibility that nonphosphorylatable forms of IkappaBalpha may be a means of preventing pathological bone loss.
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PMID:TAT fusion proteins containing tyrosine 42-deleted IkappaBalpha arrest osteoclastogenesis. 1140 88

Prophylactic thyroidectomy is recommended for carriers of RET protooncogene mutations owing to their nearly complete penetrance for medullary thyroid carcinoma (MTC). However, this guideline is challenged by mutations exhibiting variable penetrance of C-cell pathology. A 38-year-old woman presented with pathologic basal and pentagastrin-stimulated calcitonin levels. Genetic analysis revealed a heterozygous RET protooncogene germline mutation in codon 791 (exon 13) (TAT(Tyr)-->TTT(Phe)), followed by thyroidectomy and systematic central lymph node dissection. Histology showed C-cell hyperplasia (CCH) only. Three additional carriers were identified among family members. The 71-year-old father refused surgery despite pathologic calcitonin levels. The index patient's 37-year-old sister had normal basal and stimulated calcitonin levels, and her 6-year-old son had a 10-fold rise of calcitonin after pentagastrin stimulation. Both patients underwent the same operation as the index patient. The sister had 25 hyperplastic C-cells, but the her son had extensive CCH without MTC. The eldest uncle of the index patient had died of metastatic MTC at the age of 52 with unknown carrier status. Despite variable penetrance, each carrier of a RET protooncogene germline mutation should undergo thyroidectomy, even if basal and stimulated calcitonin levels are normal because at present no test can exclude or predict the age of development of MTC. Moreover, pathologic calcitonin levels cannot differentiate between CCH and MTC. Central lymph node dissection is recommended, as lymph node metastases occur early, significantly worsening the prognosis.
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PMID:Surgical strategy in a kindred with a rare RET protooncogene mutation of variable penetrance with regard to multiple endocrine neoplasia. 1220 48


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