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GPI or Glucose-6-phosphate isomerase, is a protein, part of the multifunctional phosphoglucose isomerase family, which its members take part in energy pathways. GPI is a dimeric enzyme that enhances the isomerization of glucose-6-phosphate and fructose-6- phosphate (both reversible). In mammals, GPI acts as an angiogenic factor & tumor-secreted cytokine. The enzyme also acts as a neurotrophic factor for spinal & sensory neurons.

Glucose-6-phosphate isomerase (GPI) is a part of the GPI family whose members encode multifunctional phosphoglucose isomerase proteins involved in energy pathways. GPI is a dimeric enzyme which catalyzes the reversible isomerization of glucose-6-phosphate and fructose-6-phosphate. Mammalian GPI also functions as a tumor-secreted cytokine and an angiogenic factor (AMF) which stimulates endothelial cell motility. In addition, GPI is a neurotrophic factor (Neuroleukin) for spinal and sensory neurons. GPI performs in different capacities inside and outside the cell. In the cytoplasm, GPI is involved in glycolysis and gluconeogenesis, while outside the cell it acts as a neurotrophic factor for spinal and sensory neurons.
Defects in the GPI gene cause the nonspherocytic hemolytic anemia and a severe enzyme deficiency can be linked to hydrops fetalis, immediate neonatal death and neurological impairment.

Dsb proteins (DsbA, DsbB, DsbC, and DsbD) catalyze formation and isomerization of protein disulfide bonds in the periplasm of Escherichia coli. DsbC is periplasmic enzyme known as a disulfide isomerase and can convert aberrant disulfide bonds to correct ones.

Isopentenyl-diphosphate isomerase 1 (IDI1) belongs to the IPP isomerase type I family and is involved in cholesterol biosynthesis. IDI1 is a peroxisomally-localized enzyme which catalyzes the interconversion of isopentenyl diphosphate (IPP) to its highly electrophilic isomer, dimethylallyl diphosphate (DMAPP), which is the substrate for the sequential reaction that results in the synthesis of farnesyl diphosphate and, eventually, cholesterol. Peroxisomal deficiency diseases such as Zellweger syndrome and neonatal adrenoleukodystrophy show a reduction in IPP isomerase activity.

MPI is a member of the mannose-6-phosphate isomerase type 1 family. Although MPI is expressed in all tissues, it can be found more abundantly in heart, brain and skeletal muscle. Localized to the cytoplasm, MPI exploits zinc as a cofactor and catalyzes the interconversion of fructose-6-phosphate and mannose-6-phosphate. Mutations in the MPI gene are the cause of carbohydrate-deficient glycoprotein syndrome, type Ib.

Peptidyl-prolyl cis-trans isomerase NIMA-interacting 4 (PIN4) is a peptidyl-prolyl cis/trans isomerase (PPIase) which interacts with NIMA and is vital for cell cycle regulation. PIN4 has 2 different isoforms: PAR14 and PAR17. Furthermore, Pin4 protein binds to double-stranded DNA under physiological salt conditions.

Enoyl-CoA Delta Isomerase 1 (ECI1) is a main mitochondrial enzyme which takes part in beta-oxidation of unsaturated fatty acids. ECI1 is a member of the hydratase/isomerase superfamily. ECI1 catalyzes the transformation of 3-cis and 3-trans-enoyl-CoA esters to the 2-trans-enoylCoA intermediates.

TPI1 is one of the triosephosphate isomerase family. TPI1 catalyzes the isomerization of glyceraldehydes 3-phosphate (G3P) and dihydroxy-acetone phosphate (DHAP) in glycolysis and gluconeogenesis. Mutations in TPI1 causes triosephosphate isomerase deficiency (TPI deficiency). TPI deficiency is an autosomal recessive disorder which is the most severe clinical disorder of glycolysis and is related to neonatal jaundice, chronic hemolytic anemia, progressive neuromuscular dysfunction, cardiomyopathy and increased susceptibility to infection.

TPI1 is one of the triosephosphate isomerase family. TPI1 catalyzes the isomerization of glyceraldehydes 3-phosphate (G3P) and dihydroxy-acetone phosphate (DHAP) in glycolysis and gluconeogenesis. Mutations in TPI1 causes triosephosphate isomerase deficiency (TPI deficiency). TPI deficiency is an autosomal recessive disorder which is the most severe clinical disorder of glycolysis and is related to neonatal jaundice, chronic hemolytic anemia, progressive neuromuscular dysfunction, cardiomyopathy and increased susceptibility to infection.

Ribose-5-phosphate isomerase (RPIA) is a member of the ribose 5-phosphate isomerase family. RPIA is an enzyme which catalyzes the conversion between ribose-5-phosphate (R5P) and ribulose-5-phosphate (Ru5P). RPI occurs as 2 separate proteins forms, termed RPIA and RPIB. RPIA has a vital role in the metabolism of plants and animals, as it is involved in the Calvin cycle which takes place in plants, and the pentose phosphate pathway which occurs in plants as well as animals.

PECI is an enzyme that localized to the peroxisomal matrix and encloses one ACB (acyl-CoA-binding) domain. PECI is expressed abundantly in liver, heart and skeletal muscle. PECI functions to catalyze the isomerization of both 3-cis and 3-trans double bonds into the 2-trans form in an array of enoyl-CoA species. PECI takes part in the beta-oxidation of unsaturated fatty acids.

Protein disulfide isomerases (PDIs) constitute a family of structurally related enzymes which catalyze disulfide bonds formation, reduction, or isomerization of newly synthesized proteins in the lumen of the endoplasmic reticulum (ER). They act also as chaperones, and are, therefore, part of a quality-control system for the correct folding of the proteins in the same subcellular compartment. PDI has been found to have moderate effects (25-fold) on the rate of oxidative folding of proteins in vitro.
Recombinant Human Protein Disulfide Isomerase is involved in disulphide-bond formation and isomerization, as well as the reduction of disulphide bonds in proteins. Recombinant PDI has been found to have moderate effects (25-fold) on the rate of oxidative folding of proteins in vitro.

SlyD accessiton#: NP_755987 is a putative folding helper protein from the Escherichia coli cytosol, which has N-terminal prolyl isomerase domain of the FKBP type and a most likely unstructured C-terminal tail. SlyD is an important factor in the biosynthesis of the metal cluster in the [NiFe]-hydrogenase enzymes, and exhibits several activities including that of a peptidyl-prolyl isomerase.

PDIA6 belongs to the protein disulfide isomerase family (PDI). PDIA6 is an enzyme in the endoplasmic reticulum in eukaryotes or periplasmic space of prokaryotes which catalyzes the formation and breakage of disulfide bonds between cysteine residues within proteins as they fold. PDIA6 functions as a chaperone that inhibits aggregation of misfolded proteins. PDIA6, also has a role in platelet aggregation and activation by agonists such as convulxin, collagen and thrombin.

Isopentenyl-diphosphate Delta-isomerase 2 (IDI2) is a member of the IPP isomerase type 1 family. IDI2 catalyzes the 1,3-allylic reorganization of the homoallylic substrate isopentenyl (IPP) to its extremely electrophilic allylic isomer, dimethylallyl diphosphate (DMAPP).

PDIA4 is an endoplasmic reticulum luminal protein that is a stress protein as well as a member of the protein disulfide isomerase family of proteins. PDIA4 participates in the catalysis of protein-S-S-bond rearrangement. PDIA4 and PDIA3 function as proteases, protein disulfide isomerases, phospholipases or an arrangement of these.

PDIA3 is an enzyme that belongs to the endoplasmic reticulum and interacts with lectin chaperones calreticulin and calnexin to modulate folding of newly synthesized glycoproteins. PDIA3 has protein disulfide isomerase activity. Complexes of lectins and PDIA3 mediate protein folding by promoting formation of disulfide bonds in their glycoprotein substrates. PDIA3 is expressed in the lumbar spinal cord from rats submitted to peripheral lesion during neonatal period. PDIA3 interacts with thiazide-sensitive sodium-chloride cotransporter in the kidney and is induced by glucose deprivation. PDIA3 is part of the major histocompatibility complex (MHC) class I peptide-loading complex (TAP1), which is important for formation of the final antigen conformation and export from the endoplasmic reticulum to the cell surface.

Cyclophilin-D is a member of the peptidyl-prolyl cis-trans isomerase (PPIase) family. PPIases catalyze the cis-trans isomerization of proline imidic peptide bonds in oligopeptides and speeds up the protein folding. Cyclophilin-D possess PPIase activity and binds to the immunosuppressant cyclosporin-A. Cyclophilin-D is very well known that its overexpression suppresses the apoptosis in cancer cell. Cyclophilin-D suppresses apoptotic cell death by the use of mitochondrial hexokinase-2 dependent mechanism in cancer cells.

PDIA4 is an endoplasmic reticulum luminal protein that is a stress protein as well as a member of the protein disulfide isomerase family of proteins. PDIA4 participates in the catalysis of protein-S-S-bond rearrangement. PDIA4 and PDIA3 function as proteases, protein disulfide isomerases, phospholipases or an arrangement of these.

Dopachrome Tautomerase also known as DCT, belongs to the tyrosinase family. DCT takes a significant part in the synthesis of the melanin pigment including tyrosinase (Tyr), tyrosinase-related protein 1 (Tyrp1). Which are highly involved in eumelanin synthesis. The change among the eumelanin and the pheomelanin pathways is assumed to depend on the presence of cysteine. Hence, in the lack of cysteine, dopaquinone, the product of tyrosinase action, is transformed to cyclodopa (leucodopachrome) and afterwards to dopachrome (and DOPA).

TOP1 is an important nuclear enzyme that interconverts supercoiled DNA to the necessary topological conformations for standard DNA replication and transcription. TOP1 is the target antigen for TOP1 autoantibodies. TOP1 antibodies are a specific marker in scleroderma patients (specificity 98-100%) and are related with the existence of diffuse skin involvement and pulmonary fibrosis. In human tissues top1 enzyme is primarily synthesized as a protein with a molecular weight of 100-kDa. Most of this precursor is then proteolytically processed to a 70-kDa size, from which the TOP1 antigen has derived its name.

DNA toposisomerase I is a key nuclear enzyme that interconverts supercoiled DNA to the required topological conformations for normal DNA replication and transcription. This enzyme is the target antigen for the so-called Scl-70 autoantibodies. Scl-70 antibodies are a specific marker in Scleroderma patients (specificity 98-100%) and are associated with the presence of diffuse skin involvement and pulmonary fibrosis.
In human tissues the DNA topoisomerase I is initially synthesized as a protein with 100 kDa molecular weight. Most of this precursor is then proteolytically processed to a species with 70 kDa molecular weight from which the Scl-70 antigen has derived its name.

PDIA6 belongs to the protein disulfide isomerase family (PDI). PDIA6 is an enzyme in the endoplasmic reticulum in eukaryotes or periplasmic space of prokaryotes which catalyzes the formation and breakage of disulfide bonds between cysteine residues within proteins as they fold. PDIA6 functions as a chaperone that inhibits aggregation of misfolded proteins. PDIA6, also has a role in platelet aggregation and activation by agonists such as convulxin, collagen and thrombin.

TOP1 is an important nuclear enzyme that interconverts supercoiled DNA to the necessary topological conformations for standard DNA replication and transcription. TOP1 is the target antigen for TOP1 autoantibodies. TOP1 antibodies are a specific marker in scleroderma patients (specificity 98-100%) and are related with the existence of diffuse skin involvement and pulmonary fibrosis. In human tissues top1 enzyme is primarily synthesized as a protein with a molecular weight of 100-kDa. Most of this precursor is then proteolytically processed to a 70-kDa size, from which the TOP1 antigen has derived its name.