Aspartate aminotransferase structure

Liver. In humans, chronic Cd exposure does not typically result in hepatotoxicity. In laboratory animals, the liver accumulates the largest concentrations of Cd after acute or chronic exposures. In chronically exposed rats, liver injury occurs prior to renal dysfunction. Chronic Cd effects in the liver include increased plasma activities of alanine and aspartate aminotransferases, structural irregularities in hepatocytes, and decreased microsomal mixed function oxidase and CYP450 activities. Acute exposures in rats result in hepatic necrosis, particularly in parenchymal cells. Additionally, rough endoplasmic reticulum deteriorates, while smooth endoplasmic reticulum proliferates. Mitochondria are also degraded. As is the case with chronic exposure, microsomal mixed function oxidases and CYP450s are inhibited. 

Brunger AT (1988) Crystallographic refinement by simulated annealing. Application to a 2.8 A resolution structure of aspartate aminotransferase. J Mol Biol 203(3) 803-816... 

Figure 2-10 Ramachandran plot for cytosolic aspartate aminotransferase. The angles and / were determined experimentally from X-ray diffraction data at 0.16 nm resolution and model building. The majority of conformations are those of a helices or of P structure. Glycine residues are indicated by filled circles, while all other residues are denoted by an "x". One of these (green) lies quite far from an allowed area and must give rise to localized strain.104b Extreme lower limit "allowed" regions by the hard-sphere criteria are shown in outline. From coordinates of Arthur Amone et al. (unpublished).106...

Many enzymes exist within a cell as two or more isoenzymes, enzymes that catalyze the same chemical reaction and have similar substrate specificities. They are not isomers but are distinctly different proteins which are usually encoded by different genes.22 23 An example is provided by aspartate aminotransferase (Fig. 2-6) which occurs in eukaryotes as a pair of cytosolic and mitochondrial isoenzymes with different amino acid sequences and different isoelectric points. Although these isoenzymes share less than 50% sequence identity, their internal structures are nearly identical.24-27 The two isoenzymes, which also share structural homology with that of E. coli,28 may have evolved separately in the cytosol and mitochondria, respectively, from an ancient common precursor. Tire differences between them are concentrated on the external surface and may be important to as yet unknown interactions with other protein molecules. 

Figure 14-6 Drawing showing pyridoxal phosphate (shaded) and some surrounding protein structure in the active site of cytosolic aspartate aminotransferase. This is the low pH form of the enzyme with an N-protonated Schiff base linkage of lysine 258 to the PLP. The tryptophan 140 ring lies in front of the coenzyme. Several protons, labeled Ha, Hb, and Hd are represented in NMR spectra by distinct resonances whose chemical shifts are sensitive to changes in the active site.169...

Aspartate aminotransferase 57s, 135s, 753 absorption spectra 749 active site structure 744 atomic structure 750 catalytic intermediates, models 752 NMR spectra 149 quinonoid intermediate 750 Ramachandran plot 61 sequence 57 transamination 742 Aspartate ammonia-lyase 685 Aspartate carbamoyltransferase 348s active sites 348 regulation 540... 

Thiosulfate cyanide sulfurtransferase symmetry in 78 TTiiouridine 234 Three-dimensional structures of aconitase 689 adenylate kinase 655 aldehyde oxido-reductase 891 D-amino acid oxidase 791 a-amylase, pancreatic 607 aspartate aminotransferase 57,135 catalytic intermediates 752 aspartate carbamyltransferase 348 aspartate chemoreceptor 562 bacteriophage P22 66 cadherin 408 calmodulin 317 carbonic acid anhydrase I 679 carboxypeptidase A 64 catalase 853 cholera toxin 333, 546 chymotrypsin 611 citrate synthase 702, 703 cutinase 134 cyclosporin 488 cytochrome c 847 cytochrome c peroxidase 849 dihydrofolate reductase 807 DNA 214, 223,228,229, 241 DNA complex... 

Most of the synthetic androgens and anabolic agents are 17-alkyl-substituted steroids. Administration of drugs with this structure is often associated with evidence of hepatic dysfunction, eg, increase in sulfobromophthalein retention and aspartate aminotransferase (AST) levels. Alkaline phosphatase values are also elevated. These changes usually occur early in the course of treatment, and the degree is proportionate to the dose. Bilirubin levels occasionally increase until clinical jaundice is apparent. The cholestatic jaundice is reversible upon cessation of therapy, and permanent changes do not occur. In older males, prostatic hyperplasia may develop, causing urinary retention. 

Active site structure of Escherichia coli aspartate aminotransferase (see Chapter 5 for details). 

Jansonius, J. N., and Vincent, M. G. (1987). Structural Basis for Catalysis by Aspartate Aminotransferase. (Biological Macromolecules and Assemblies, Vol. 

A. T. Brunger, J. Mol. Biol., 203, 803 (1988). Crystallographic Refinement by Simulated Annealing. Application to a 2.8 A Resolution Structure of Aspartate Aminotransferase. 

Fig. 8.10 X-ray crystal structure of an aspartate aminotransferase (AspAT) bound to its cofactor pyridoxal 5 -phosphate and aspartate. Directed evolution techniques produced changes in ligand specificity due to substitution of the disparate positions indicated. Coordinates from lART [25].

Fasella P and Turano C (1970) Structure and catalytic role of the functional groups of aspartate aminotransferase. Vitamins and Hormones 157-94. 

Many of the enzymes that catalyze these reactions, such as serine hy- droxymethyltransferase, which converts serine into glycine, have the same fold as that of aspartate aminotransferase and are clearly related by divergent evolution. Others, such as tryptophan synthetase, have quite different overall structures. Nonetheless, the active sites of these enzymes are remarkably similar to that of aspartate aminotransferase, revealing the effects of convergent evolution. 

J. Jager, M. Moser, U. Sauder, and J.N. Jansonius. 1994. Crystal structures of Escherichia coli aspartate aminotransferase in two conformations Comparison of an unliganded open and two liganded closed forms J. Mol. Biol. 239 285-305. (PubMed)... 

Aspartate aminotransferase is the prototype of a large family of PLP-dependent enzymes. Comparisons of amino acid sequences as well as several three-dimensional structures reveal that almost all transaminases having roles in amino acid biosynthesis are related to aspartate aminotransferase by divergent evolution. An examination of the aligned amino acid sequences reveals that two residues are completely conserved. These residues are the lysine residue that forms the Schiff base with the pyridoxal phosphate cofactor (lysine 258 in aspartate aminotransferase) and an arginine residue that interacts with the a-carboxylate group of the ketoacid (see Figure 23.11). 

The a subunit catalyzes the formation of indole from indole-3-glycerol phosphate, whereas each P subunit has a PLP-containing active site that catalyzes the condensation of indole and serine to form tryptophan. The overall three-dimensional structure of this enzyme is distinct from that of aspartate aminotransferase and the other PLP enzymes already discussed. Serine forms a Schiff base with this PLP, which is then dehydrated to give the Schiffbase of aminoacrylate. This reactive intermediate is attacked by indole to give tryptophan. 

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