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4lvc

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== Publication Abstract from PubMed ==
== Publication Abstract from PubMed ==
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S-Adenosyl-L-homocysteine hydrolase (SAHase) catalyzes the reversible breakdown of S-adenosyl-L-homocysteine (SAH) to adenosine and homocysteine. SAH is formed in methylation reactions that utilize S-adenosyl-L-methionine (SAM) as a methyl donor. By removing the SAH byproduct, SAHase serves as a major regulator of SAM-dependent biological methylation reactions. Here, the first crystal structure of SAHase of plant origin, that from the legume yellow lupin (LlSAHase), is presented. Structures have been determined at high resolution for three complexes of the enzyme: those with a reaction byproduct/substrate (adenosine), with its nonoxidizable analog (cordycepin) and with a product of inhibitor cleavage (adenine). In all three cases the enzyme has a closed conformation. A sodium cation is found near the active site, coordinated by residues from a conserved loop that hinges domain movement upon reactant binding. An insertion segment that is present in all plant SAHases is located near a substrate-pocket access channel and participates in its formation. In contrast to mammalian and bacterial SAHases, the channel is open when adenosine or cordycepin is bound and is closed in the adenine complex. In contrast to SAHases from other organisms, which are active as tetramers, the plant enzyme functions as a homodimer in solution.
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S-Adenosyl-L-homocysteine hydrolase (SAHase) is involved in the enzymatic regulation of S-adenosyl-L-methionine (SAM)-dependent methylation reactions. After methyl-group transfer from SAM, S-adenosyl-L-homocysteine (SAH) is formed as a byproduct, which in turn is hydrolyzed to adenosine (Ado) and homocysteine (Hcy) by SAHase. The crystal structure of BeSAHase, an SAHase from Bradyrhizobium elkanii, which is a nitrogen-fixing bacterial symbiont of legume plants, was determined at 1.7 A resolution, showing the domain organization (substrate-binding domain, NAD(+) cofactor-binding domain and dimerization domain) of the subunits. The protein crystallized in its biologically relevant tetrameric form, with three subunits in a closed conformation enforced by complex formation with the Ado product of the enzymatic reaction. The fourth subunit is ligand-free and has an open conformation. The BeSAHase structure therefore provides a unique snapshot of the domain movement of the enzyme induced by the binding of its natural ligands.
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High-resolution structures of complexes of plant S-adenosyl-L-homocysteine hydrolase (Lupinus luteus).,Brzezinski K, Dauter Z, Jaskolski M Acta Crystallogr D Biol Crystallogr. 2012 Mar;68(Pt 3):218-31. Epub 2012 Feb 7. PMID:22349223<ref>PMID:22349223</ref>
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An enzyme captured in two conformational states: crystal structure of S-adenosyl-L-homocysteine hydrolase from Bradyrhizobium elkanii.,Manszewski T, Singh K, Imiolczyk B, Jaskolski M Acta Crystallogr D Biol Crystallogr. 2015 Dec 1;71(Pt 12):2422-32. doi:, 10.1107/S1399004715018659. Epub 2015 Nov 26. PMID:26627650<ref>PMID:26627650</ref>
From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>

Revision as of 06:59, 16 December 2015

Crystal structure of S-adenosyl-L-homocysteine hydrolase from Bradyrhizobium elkanii in complex with adenosine

4lvc, resolution 1.74Å

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