Structures of adenylosuccinate synthetase from Triticum aestivum and Arabidopsis thaliana 1 1Edited by R. Huber

Prade, Lars; Cowan‐Jacob, Sandra W.; Chemla, Philippe; Potter, Sharon; Ward, Eric; Fonné‐Pfister, Raymonde

doi:10.1006/jmbi.1999.3473

Cited by 27 publications

(30 citation statements)

References 17 publications

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“…At subunit concentrations below 10 M, and in the absence of active site ligands, the E. coli synthetase is largely monomeric (12) and presumably inactive, although the latter has yet to be demonstrated. Synthetases from plants reportedly behave as monomers in gel filtration, but light scattering data are consistent with a dimer (19). The basic isozyme is reportedly a stable dimer (2, 3, 21, 39).…”

Section: Resultsmentioning

confidence: 91%

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Recombinant Mouse Muscle Adenylosuccinate Synthetase

Iancu¹,

Borza²,

Choe

et al. 2001

Journal of Biological Chemistry

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Vertebrates possess two isozymes of adenylosuccinate synthetase. The acidic isozyme is similar to the synthetase from bacteria and plants, being involved in the de novo biosynthesis of AMP, whereas the basic isozyme participates in the purine nucleotide cycle. Reported here is the first instance of overexpression and crystal structure determination of a basic isozyme of adenylosuccinate synthetase. The recombinant mouse muscle enzyme purified to homogeneity in milligram quantities exhibits a specific activity comparable with that of the rat muscle enzyme isolated from tissue and K m parameters for GTP, IMP, and L-aspartate (12, 45, and 140 M, respectively) similar to those of the enzyme from Escherichia coli. The mouse muscle and E. coli enzymes have similar polypeptide folds, differing primarily in the conformation of loops, involved in substrate recognition and stabilization of the transition state. Residues 65-68 of the muscle isozyme adopt a conformation not observed in any previous synthetase structure. In its new conformation, segment 65-68 forms intramolecular hydrogen bonds with residues essential for the recognition of IMP and, in fact, sterically excludes IMP from the active site. Observed differences in ligand recognition among adenylosuccinate synthetases may be due in part to conformational variations in the IMP pocket of the ligand-free enzymes.

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Section: Resultsmentioning

confidence: 91%

“…IMP alone may stabilize the synthetase dimer and by itself triggers conformational changes in the active site of the E. coli synthetase. 1 However, recent structures of the synthetase from plants, Arabidopsis thaliana and Triticum aestivum, reveal organized active sites in the presence of GDP alone (19).…”

mentioning

confidence: 99%

Recombinant Mouse Muscle Adenylosuccinate Synthetase

Iancu¹,

Borza²,

Choe

et al. 2001

Journal of Biological Chemistry

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“…The K d value for the mammalian isozymes then, in the absence of ligands, is significantly lower than that of E. coli synthetase (34). The molecular weight (78 kDa) of a yeast synthetase, determined by gel filtration, lies between that of a monomer and dimer (40), whereas plant synthetases are either monomers or dimers, depending on the methodology of mass determination (41 (Table I). AdSS2-Tr has a slightly higher K m value for L-aspartate than that of AdSS2.…”

Section: Sequencementioning

confidence: 99%

Variations in the Response of Mouse Isozymes of Adenylosuccinate Synthetase to Inhibitors of Physiological Relevance

Borza

Iancu

Pike

et al. 2003

Journal of Biological Chemistry

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Vertebrates have acidic and basic isozymes of adenylosuccinate synthetase, which participate in the first committed step of de novo AMP biosynthesis and/or the purine nucleotide cycle. These isozymes differ in their kinetic properties and N-leader sequences, and their regulation may vary with tissue type. Recombinant acidic and basic synthetases from mouse, in the presence of active site ligands, behave in analytical ultracentrifugation as dimers. Active site ligands enhance thermal stability of both isozymes. Truncated forms of both isozymes retain the kinetic parameters and the oligomerization status of the full-length proteins. AMP potently inhibits the acidic isozyme competitively with respect to IMP. In contrast, AMP weakly inhibits the basic isozyme noncompetitively with respect to all substrates. IMP inhibition of the acidic isozyme is competitive, and that of the basic isozyme noncompetitive, with respect to GTP. Fructose 1,6-bisphosphate potently inhibits both isozymes competitively with respect to IMP but becomes noncompetitive at saturating substrate concentrations. The above, coupled with structural information, suggests antagonistic interactions between the active sites of the basic isozyme, whereas active sites of the acidic isozyme seem functionally independent. Fructose 1,6-bisphosphate and IMP together may be dynamic regulators of the basic isozyme in muscle, causing potent inhibition of the synthetase under conditions of high AMP deaminase activity.

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“…Indeed, in crystal structures of adenylosuccinate synthetase from Arabidopsis thaliana and Triticum aestivum, GDP alone is present in ordered active sites (24). Unfortunately, the ligand-free conformations of the plant synthetases are unavailable.…”

Section: Discussionmentioning

confidence: 99%