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)

Guanidinoacetate methyltransferase (GAMT) is the enzyme that catalyzes the last step of creatine biosynthesis. The enzyme is found in abundance in the livers of all vertebrates. Recombinant rat liver GAMT has been crystallized with S-adenosylhomocysteine (SAH), and the crystal structure has been determined at 2.5 A resolution. The 36 amino acid residues at the N terminus were cleaved during the purification and the truncated enzyme was crystallized. The truncated enzyme forms a dimer, and each subunit contains one SAH molecule in the active site. Arg220 of the partner subunit forms a pair of hydrogen bonds with Asp134 at the guanidinoacetate-binding site. On the basis of the crystal structure, site-directed mutagenesis on Asp134, and chemical modification and limited proteolysis studies, we propose a catalytic mechanism of this enzyme. The truncated GAMT dimer structure can be seen as a ternary complex of protein arginine methyltransferase (one subunit) complexed with a protein substrate (the partner subunit) and the product SAH. Therefore, this structure provides insight into the structure and catalysis of protein arginine methyltransferases.
J Mol Biol 2002 Jul 05
PMID:Crystal structure of guanidinoacetate methyltransferase from rat liver: a model structure of protein arginine methyltransferase. 1207 81

Maternal mild hyperhomocysteinemia is associated with increased risk for bearing children with neural tube defects (NTD). Folate intake corrects hyperhomocysteinemia and prevents up to 70% of NTD. The curly-tail (ct) mouse, an animal model for NTD, has been suggested to display features that closely resemble the human defect. We therefore investigated folate metabolism in ct mice. On control and folate-/choline-deficient diets, ct mice exhibited higher plasma homocysteine levels than control C57Bl/6 mice. This increase was associated with increased liver S-Adenosylhomocysteine and decreased S-adenosylmethionine:S-adenosylhomocysteine (SAM/SAH) ratios. Since the ct locus maps in close proximity to the gene for methylenetetrahydrofolate reductase (Mthfr), a modifier of homocysteine levels in man, we also assayed Mthfr activity and sequenced the 5(') regulatory region; these experiments suggested that Mthfr is not defective in the ct strain. Finally, we examined the influence of dietary folate on NTD incidence in the ct strain, but did not identify significant differences among the four diets used in the study. Our work suggests that altered homocysteine metabolism may contribute to the pathogenetic mechanism of the ct defect, but, unlike human NTD, nutritional or genetic deficiencies in folate metabolism do not appear to play a significant direct role.
Mol Genet Metab 2002 Aug
PMID:The curly-tail (ct) mouse, an animal model of neural tube defects, displays altered homocysteine metabolism without folate responsiveness or a defect in Mthfr. 1220 34

Our previous studies showed that S-adenosyl-methionine (SAM) induced Parkinson's disease-like changes in rat. It caused death to dopamine neurons in the substantia nigra, which appeared shrunken and fragmented, indicative of apoptosis-like changes (Charlton and Crowell [1995] Mol. Chem. Neuropathol. 26:269-284; Charlton [1997] Life Sci. 61:495-502). In this study, we investigated whether SAM causes apoptosis in both undifferentiated PC12 (PC12) cells and nerve growth factor (NGF)-differentiated PC12 (D-PC12) cells. S-adenosyl-homocysteine (SAH), the nonmethyl analog of SAM, was also tested. SAM and SAH (1.0 nM to 10.0 microM) caused lactate dehydrogenase (LDH) release from the PC12 cells and D-PC12 cells; cells with morphological changes and fluorescent DNA fragmentation staining were detected among both PC12 cell and D-PC12 cell. Compared with the PC12 cell, the D-PC12 cell, a postmitotic cell, was more sensitive to the toxic effects of SAM or SAH and presented much greater LDH release, suggesting a lethal effect; surprisingly, the amounts of apoptotic cells did not differ significantly between the two kinds of cells. In medium deprived of exogenous methionine, a decline in LDH release was observed in PC12 and D-PC12 cells. Also, lower levels of intracellular SAM and SAH were observed in the methionine-deleted media, which were reversed by the addition of either SAM or SAH. An antivitamin B(12) monoclonal antibody was added to methionine-depleted medium, resulting in deficiency of both endogenous and exogenous methionine, which caused further decreases in LDH release and reduction in the levels of intracellular SAM and SAH. The preliminary data showed different sensitivities to SAM or SAH between PC12 cell and D-PC12 cells, which suggests that PC12 cell may be more stable as a metabolic model. Apoptosis of PC12 cells was also assessed by PARP cleavage detection, Western blot analysis of Bax and Bcl-2 proteins, and DNA laddering on agarose gel electrophoresis. The proapoptoic protein Bax was dominantly expressed, whereas Bcl-2 was slightly down-regulated by SAM. SAH weakly induced the expression of Bax and slightly decreased Bcl-2 levels. The effects of SAM and its analog, SAH, were demonstrated conclusively to induce apoptosis in PC12 cells.
 ...
PMID:S-adenosyl-methionine-induced apoptosis in PC12 cells. 1221 Aug 45

Kinetic analysis of methyl group transfer from S-adenosyl-L-methionine (SAM) to the GATC recognition site catalyzed by the phage T4 DNA-[N6-adenine]-methyltransferase (MTase) [EC 2.1.1.72] showed that the reverse reaction is at least 500 times slower than the direct one. The overall pattern of product inhibition corresponds to an ordered steady-state mechanism following the sequence SAM decreases DNA decreases metDNA increases SAH increases (S-adenosyl-L-homocysteine). Pronounced inhibition was observed at high concentrations of the 20-meric substrate duplex, which may be attributed to formation of a dead-end complex MTase-SAH-DNA. In contrast, high SAM concentrations proportionally accelerated the reaction. Thus, the reaction may include a stage whereby the binding of SAM and the release of SAH are united into one concerted event. Computer fitting of alternative kinetic schemes to the aggregate of experimental data revealed that the most plausible mechanism involves isomerization of the enzyme.
Mol Biol (Mosk)
PMID:[The kinetic mechanism of phage T4 DNA-[N6-adenine]-methyltransferase]. 1239 49

Kinetic analysis of methyl group transfer from S-adenosyl-L-methionine (SAM) to the 5'-GGATCC recognition site catalyzed by the DNA-[N4-cytosine]-methyltransferase from Bacillus amyloliquefaciens [EC 2.1.1.113] has shown that the dependence of the rate of methylation of the 20-meric substrate duplex on SAM and DNA concentration are normally hyperbolic, and the maximal rate is attained upon enzyme saturation with both substrates. No substrate inhibition is observed even at concentrations many times higher than the Km values (0.107 microM for DNA and 1.45 microM for SAM), which means that no nonreactive enzyme-substrate complexes are formed during the reaction. The overall pattern of product inhibition corresponds to an ordered steady-state mechanism following the sequence SAM decreases DNA decreases metDNA increases SAH increases (S-adenosyl-L-homocysteine). However, more detailed numerical analysis of the aggregate experimental data admits an alternative order of substrate binding, DNA decreases SAM decreases, though this route is an order of magnitude slower.
Mol Biol (Mosk)
PMID:[DNA-[N4-cytosine]-methyltransferase from Bacillus amyloliquefaciens: mechanism of action derived from steady state kinetics]. 1262 55

Extracellular ATP, adenosine (Ado), and adenosine plus homocysteine (Ado/HC) cause apoptosis of cultured pulmonary artery endothelial cells through the enhanced formation of intracellular S-adenosylhomocysteine and disruption of focal adhesion complexes. Because an increased intracellular ratio of S-adenosylhomocysteine/S-adenosylmethionine favors inhibition of methylation, we hypothesized that Ado/HC might act by inhibition of isoprenylcysteine-O-carboxyl methyltransferase (ICMT). We found that N-acetyl-S-geranylgeranyl-L-cysteine (AGGC) and N-acetyl-S-farnesyl-L-cysteine (AFC), which inhibit ICMT by competing with endogenous substrates for methylation, caused apoptosis. Transient overexpression of ICMT inhibited apoptosis caused by Ado/HC, UV light exposure, or tumor necrosis factor-alpha. Because the small GTPase, Ras, is a substrate for ICMT and may modulate apoptosis, we also hypothesized that inhibition of ICMT with Ado/HC or AGGC might cause endothelial apoptosis by altering Ras activation. We found that ICMT inhibition decreased Ras methylation and activity and the activation of the downstream signaling molecules Akt, ERK-1, and ERK-2. Furthermore, overexpression of wild-type or dominant active H-Ras blocked Ado/HC-induced apoptosis. These findings suggest that inhibition of ICMT causes endothelial cell apoptosis by attenuation of Ras GTPase methylation and activation and its downstream antiapoptotic signaling pathway.
Mol Biol Cell 2003 Mar
PMID:Isoprenylcysteine carboxyl methyltransferase activity modulates endothelial cell apoptosis. 1263 8

It is unresolved whether elevated homocysteine in coronary artery disease (CAD) is the cause of arteriosclerosis or its consequence. In contrast, genetic variants of enzymes that metabolize homocysteine cannot be altered by arteriosclerosis. Consequently, their association with CAD would permit to imply causality. We modeled by regression analysis the effect of 11 variants in the methionine cycle upon CAD manifestation in 591 controls and 278 CAD patients. Among the examined variants only the carriership for the c.844ins68 in the cystathionine beta-synthase (CBS) gene was associated with a significantly lowered risk of CAD (OR=0.56; 95% CI=0.35-0.90 in the univariable, and OR=0.41, 95% CI=0.19-0.89 for obese people in the multivariable analysis, respectively). Healthy carriers of the c.844ins68 variant exhibited, compared to the wild type controls, significantly higher postload ratios of blood S-adenosylmethionine to S-adenosylhomocysteine (61.4 vs. 54.9, p=0.001) and of plasma total cysteine to homocysteine (8.6 vs. 7.3, p=0.004). The changes in these metabolites are compatible with an improved methylation status and with enhanced activity of homocysteine transsulfuration. In conclusion, the coincidence of clinical and biochemical effects of a common c.844ins68 CBS variant supports the hypothesis that compounds relating to homocysteine metabolism may play role in the development and/or progression of CAD.
Mol Genet Metab 2003 Jul
PMID:Genetic variants of homocysteine metabolizing enzymes and the risk of coronary artery disease. 1285 21

DIM-5 is a SUV39-type histone H3 Lys9 methyltransferase that is essential for DNA methylation in N. crassa. We report the structure of a ternary complex including DIM-5, S-adenosyl-L-homocysteine, and a substrate H3 peptide. The histone tail inserts as a parallel strand between two DIM-5 strands, completing a hybrid sheet. Three post-SET cysteines coordinate a zinc atom together with Cys242 from the SET signature motif (NHXCXPN) near the active site. Consequently, a narrow channel is formed to accommodate the target Lys9 side chain. The sulfur atom of S-adenosyl-L-homocysteine, where the transferable methyl group is to be attached in S-adenosyl-L-methionine, lies at the opposite end of the channel, approximately 4 A away from the target Lys9 nitrogen. Structural comparison of the active sites of DIM-5, an H3 Lys9 trimethyltransferase, and SET7/9, an H3 Lys4 monomethyltransferase, allowed us to design substitutions in both enzymes that profoundly alter their product specificities without affecting their catalytic activities.
Mol Cell 2003 Jul
PMID:Structural basis for the product specificity of histone lysine methyltransferases. 1288 87

Guanidinoacetate methyltransferase (GAMT) is the enzyme that catalyzes the last step of creatine biosynthesis. The enzyme is found in abundance in the livers of all vertebrates. Recombinant rat liver GAMT truncated at amino acid 37 from the N-terminus has been crystallized with S-adenosylhomocysteine (SAH) in a monoclinic modification and the crystal structure has been determined at 2.8 A resolution. There are two dimers in the crystallographic asymmetric unit. Each dimer has non-crystallographic twofold symmetry and is related to the other dimer by pseudo-4(3) symmetry along the crystallographic b axis. The overall structure of GAMT crystallized in the monoclinic modification is quite similar to the structure observed in the tetragonal modification [Komoto et al. (2002), J. Mol. Biol. 320, 223-235], with the exception of the loop containing Tyr136. In the monoclinic modification, the loops in three of the four subunits have a catalytically unfavorable conformation and the loop of the fourth subunit has a catalytically favorable conformation as observed in the crystals of the tetragonal modification. From the structures in the monoclinic and tetragonal modifications, we can explain why the Y136F mutant enzyme retains considerable catalytic activity while the Y136V mutant enzyme loses the catalytic activity. The crystal structure of a Gd derivative of the tetragonal modification has also been determined. By comparing the Gd-derivative structure with the native structures in the tetragonal and the monoclinic modifications, useful characteristic features of Gd-ion binding for application in protein crystallography have been observed. Gd ions can bind to proteins without changing the native protein structures and Gd atoms produce strong anomalous dispersion signals from Cu Kalpha radiation; however, Gd-ion binding to protein requires a relatively specific geometry.
 ...
PMID:Monoclinic guanidinoacetate methyltransferase and gadolinium ion-binding characteristics. 1292 89

DNA duplexes containing a single phosphoryldisulfide link in place of the natural internucleotide phosphodiester bond were employed in affinity modification of Cys142 in cytosine-C5 DNA methyltransferase SsoII (M.SsoII). The possibility of duplex-M.SsoII conjugation as a result of disulfide exchange was demonstrated. The crosslinking efficiency proved to depend on the DNA primary structure, modification position, and the presence of S-adenosyl-L-homocysteine, a nonreactive analog of the methylation cofactor. The SH group of M.SsoII Cys142 was assumed to be close to the DNA sugar-phosphate backbone in the DNA-enzyme complex.
Mol Biol (Mosk)
PMID:[Covalent binding of Cys142 from SsoII methyltransferase with DNA duplexes, containing a phosphoryldisulfide internucleotide group]. 1459 29


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