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L-threonine to glycine degradation consists of a two-step biochemical pathway which involvs the enzymes L-threonine dehydrogenase and 2-amino-3-ketobutyrate coenzyme A ligase. L-Threonine is initially converted into 2-amino-3-ketobutyrate by L-threonine dehydrogenase. Glycine C-Acetyltransferase (GCAT) is the 2nd enzyme in this pathway, which subsequently catalyzes the reaction between 2-amino-3-ketobutyrate and coenzyme A to form glycine and acetyl-CoA. The GCAT enzyme is regard as a class II pyridoxal-phosphate-dependent aminotransferase. GCAT is strongly expressed in the heart, brain, liver and pancreas. GCAT is also found in lung.

GGCT is a member of the family of transferases, specifically the aminoacyltransferases. GGCT protein catalyzes the formation of 5-oxoproline from gamma-glutamyl dipeptides and takes an important part in glutathione homeostasis. GGCT induces release of cytochrome c from mitochondria with resultant induction of apoptosis.

Thiosulfate Sulfurtransferase Like Domain Containing 3, also known as TSTD3 contains 1 rhodanese domain which is characterized by an active site cysteine residue that has the ability to bind sulfane sulfur and catalyse sulfur transfer.

3-Hydroxy-3-Methylglutaryl-CoA Synthase 1, also known as HMGCS1 is a member of the Belongs to the HMG-CoA synthase family. HMGCS1 condenses acetyl-CoA with acetoacetyl-CoA to form HMG-CoA, which is the substrate for HMG-CoA reductase.

Aspartoacylas or ASPA, is a protein, found in several tissues such as skeletal muscle, cerebral white matter, kidney, liver & lungs. ASPA is a homodimer that catalyses the deacetylation of Nacetylaspartic acid. In order to create L-aspartate & acetate.

O-Sialoglycoprotein Endopeptidase, also known as OSGEP is a member of the KAE1 / TsaD family. OSGEP is essential for the formation of threonylcarbamoyl group on adenosine at position 37 (t6A37) in tRNAs which read codons beginning with adenine. OSGEP take a direct catalytic part in the above reaction, however other proteins of the complex are required to fulfill this activity.

QPRT is a key enzyme in the catabolism of quinolinate. QPRT is in between the tryptophannicotinamide adenine dinucleotide (NAD) pathway, resulting in the production of nicotinic acid, carbon dioxide and pyrophosphate. Rise of QPRT levels in the brain is related to the pathogenesis of neurodegenerative disorders such as epilepsy, Alzheimer's disease, and Huntington's disease.

Formylglutathione hydrolase (Esterase D) is a member of the esterase D family. Esterase D is a serine hydrolase involved in the detoxification of formaldehyde. Esterase D is active toward various substrates including O-acetylated sialic acids, and it may possibly be involved in the recycling of sialic acids. Esterase D is used as a genetic marker for retinoblastoma and Wilson's disease.

HPRT1 has a main part in the generation of purine nucleotides through the purine salvage pathway. HPRT1 primarily functions to salvage purines from degraded DNA to renewed purine synthesis. Therefore, it performs as a catalyst in the reaction between guanine and phosphoribosyl pyrophosphate to form GMP.

Uracil DNA glycosylase (UDG), or uracil-DNA glycosylase 1, is a crucial enzyme found in all life forms, involved in repairing damaged DNA by specifically removing uracil bases that are misincorporated into DNA during replication or deaminated cytosine. In various organisms, UDG goes by different names, such as b2580, JW2564, EC 3.2.2.27, DGU, UNG15, HIGM5, EC 3.2.2, HIGM4, and UNG2. Here, we delve into the E. coli UDG, examining its structure, function, and applications in molecular biology.

Structure: The crystal structure of E. coli UDG has been extensively studied, revealing that it belongs to the uracil DNA glycosylase (UDG) superfamily. The E. coli UDG monomer has 229 amino acids with a molecular weight of 25 kDa. The protein has a beta-sheet-rich structure with an alpha-helix on one side and a groove on the other side that binds to DNA. The active site of E. coli UDG contains a conserved glutamic acid residue that acts as a catalytic base to facilitate the hydrolysis of the N-glycosidic bond between uracil and the sugar phosphate backbone.

Function: E. coli UDG plays a critical role in maintaining the integrity of the genome by preventing the accumulation of mutations that can arise from the incorporation of uracil into DNA. Uracil in DNA can occur spontaneously from the deamination of cytosine or can be incorporated during DNA synthesis when dUTP is used instead of dTTP. Unrepaired uracil bases can lead to DNA damage and genomic instability, possibly resulting in cell death or disease. E. coli UDG specifically recognizes and removes uracil bases from DNA, creating an abasic site that is further processed by other repair enzymes.

Polyribonucleotide nucleotidyltransferase 1, also known as PNPT1 is predominantly localized in the mitochondrial intermembrane space and is implicated in the import of RNA to mitochondria. Mutations in PNPT1 have been connected with combined oxidative phosphorylation deficiency-13 as well as autosomal recessive nonsyndromic deafness-70. Related pseudogenes have been found on chromosomes 3 & 7.

SUMF1 is a member of the SUMF family. SUMF1 catalyzes the hydrolysis of sulfate esters by oxidizing a cysteine residue in the substrate sulfatase to an active site 3-oxoalanine residue called C-alpha-formylglycine. Alterations in this gene result in multiple sulfatase deficiency which is a lysosomal storage disorder.

Alanyl-tRNA synthetase is a member of the aminoacyl-tRNA synthetase family, key enzymes of protein biosynthesis which charge tRNA molecules with the respective amino acids. This 108 kDa protein is an autoantigen recognized by PL-12 antibodies which occur in a subset of patients with polymyositis and dermatomyositis. Preliminary data suggest that epitope spreading occurs in the autoimmune PL-12 response such that even antibodies to an isolated alanyl-tRNA molecule can develop.

Aldo-keto reductase family 1 member D1 (AKR1D1) belongs to the AKR superfamily. The AKR family proteins are soluble NADPH oxidoreductases, which have vital roles in the metabolism of drugs, carcinogens and reactive aldehydes. AKR1D1 is also responsible for the catalysis of the 5-beta-reduction of bile acid intermediates and steroid hormones that carry a delta (4)-3-1 structure. AKR1D1 is highly expressed in the liver, colon and testis. Deficiency of the AKR1D1 enzyme may contribute to hepatic dysfunction.

Heparan Sulfate 3-O-Sulfotransferase 1 (HS3ST1), is sulfotransferase which uses 3'-phospho-5'-adenylyl sulfate (PAPS) to catalyze the transfer of a sulfo group to position 3 of glucosamine residues in heparan. HS3ST1 catalyzes the rate limiting step in the biosynthesis of heparan sulfate (HSact). This modification is a vital part in the biosynthesis of anticoagulant heparan sulfate since it concludes the structure of the antithrombin pentasaccharide binding site.

Carbonic Anhydrase XIII, also known as CA13 is a member of the alpha-carbonic anhydrase family, which catalyzes the rapid interconversion of carbon dioxide and water tobicarbonate and protons, a reversible reaction which occurs relatively slowly in the absence of catalyst. Furthermore, the active siteof nearly all carbonic anhydrases contains a zinc ion; they have been classified as metalloenzymes. At least fivedistinct CA families (?, ?, ?, ? and ?) have been found. These families have no significant a.a sequence resemblance and in just about allcases are considered to be an example of convergent evolution. The ?-CAs have been demonstrated in humans.

Phosphomannomutase 1 (PMM1) is an enzyme involved in the synthesis of the GDP-mannose and dolichol-phosphate-mannose required for a number of critical mannosyl transfer reactions. PMM1 catalyzes the conversion between D-mannose 6-phosphate and D-mannose 1-phosphate which is a substrate for GDP-mannose synthesis. GDP-mannose is used for the synthesis of dolichol-phosphate-mannose, which is crucial for N-linked glycosylation and accordingly the secretion of several glycoproteins as well as for the synthesis of glycosyl-phosphatidyl-inositol (GPI) anchored proteins. Additionally, PMM1 may be responsible for the degradation of glucose-1,6-bisphosphate in ischemic brain.

Lipase Endothelial (LIPG) has extensive phospholipase activity and may be involved in lipoprotein metabolism and vascular biology. The LIPG protein is considered a member of the TG lipase family through its sequence and characteristic lid region which provides substrate specificity for enzymes of the TG lipase family. In addition, the LIPG has triglyceride lipase activities. LIPG hydrolyzes HDLs more efficiently than other lipoproteins. LIPG also binds heparin.

GPT catalyzes the reversible transamination between alanine and 2-oxoglutarate to create pyruvate and glutamate. GPT has a crucial part in the intermediary metabolism of glucose and amino acids. GPT is broadly used as an indicator of liver reliability or hepatocellular destruction in clinical tests.

UNG is a member of the Uracil-DNA glycosylase family. One of his functions is to prevent mutagenesis by eliminating uracil from DNAmolecules by cleaving the N-glycosylic bond and initiating the base-excision repair (BER) pathway. Uracil basesare formed as a result of cytosine deamination or misincorporation of dUMP residues. After a mutation is formed, the mutagenicthreat of uracil propagates through any subsequent DNA replication steps. Among the diseases associated with UNG are: congenital rubella, and immunodeficiency with hyper igm type 4.

MAO-B is a member of the flavin monoamine oxidase family. MAO-B (Monoamine oxidase B) is a flavin-containing mitochondrial enzyme that catalyzes the oxidative deamination of biogenic and xenobiotic monoamines. MAO-B controls the metabolic degradation of catecholamines and serotonin in neural and other target tissues. MAO-B is located in platelets and in DOPA-secreting neurons in the brain. MAOB and MAOA genes have an imperative function in DOPA degradation. Benzylamine and phenylethylamine are preferentially degraded by MAOB. The MAOB gene is linked to autistic traits, empathy and Asperger syndrome. Amplified levels of MAO B are identified in the brain of Alzheimer’s patients. High phenylethylamine levels in neonates as a result of low MAOB are consistent with phenylketonuria in newborns. Polymorphisms in MAO-B are connected to smoking behavior.

MAT1A catalyzes a two-step reaction that involves the transfer of the adenosyl moiety of ATP to methionine to form S-adenosylmethionine and tripolyphosphate, which is subsequently cleaved to PPi and Pi. S-adenosylmethionine is the source of methyl groups for most biological methylations. MAT1A is found as a homotetramer (MAT I) or a homodimer (MAT III) whereas a third form, MAT II (gamma), is encoded by the MAT2A gene. Mutations in MAT1A gene are associated with methionine adenosyltransferase deficiency. MAT1A expression also correlates with a differentiated phenotype, whereas liver cells expressing MAT2A present a dedifferentiated phenotype and lowered AdoMet synthesis. Likewise, NFκB and TNFα cause a switch from MAT1A to MAT2A expression in human hepatocellular carcinoma (HCC), which facilitates cancer cell growth.

HAAO is a monomeric cytosolic protein which is a member of intramolecular dioxygenases family containing nonheme ferrous iron. The HAAO protein catalyzes the synthesis of quinolinic acid (QUIN) from 3-hydroxyanthranilic acid. QUIN is an excitotoxin whose toxicity is facilitated by its ability to activate glutamate N-methyl-D-aspartate receptors. Amplified cerebral levels of QUIN may contribute to the pathogenesis of neurologic and inflammatory disorders. HAAO is widely distributed in peripheral organs, such as liver and kidney, and is also present in low amounts in the central nervous system.