1mhm: Difference between revisions

[[Image:1mhm.jpg|left|200px]]<br /><applet load="1mhm" size="350" color="white" frame="true" align="right" spinBox="true"  

S-Adenosylmethionine decarboxylase has been implicated in cell growth and differentiation and is synthesized as a proenzyme, which undergoes autocatalytic cleavage to generate an active site pyruvoyl group. In mammals, S-adenosylmethionine decarboxylase is active as a dimer in which each protomer contains one alpha subunit and one beta subunit. In many higher organisms, autocatalysis and decarboxylation are stimulated by putrescine, which binds in a buried site containing numerous negatively charged residues. In contrast, plant S-adenosylmethionine decarboxylases are fully active in the absence of putrescine, with rapid autocatalysis that is not stimulated by putrescine. We have determined the structure of the S-adenosylmethionine decarboxylase from potato, Solanum tuberosum, to 2.3 A resolution. Unlike the previously determined human enzyme structure, the potato enzyme is a monomer in the crystal structure. Ultracentrifugation studies show that the potato enzyme is also a monomer under physiological conditions, with a weak self-association constant of 6.5 x 10(4) M(-)(1) for the monomer-dimer association. Although the potato enzyme contains most of the buried charged residues that make up the putrescine binding site in the human enzyme, there is no evidence for a putrescine binding site in the potato enzyme. Instead, several amino acid substitutions, including Leu13/Arg18, Phe111/Arg114, Asp174/Val181, and Phe285/His294 (human/potato), provide side chains that mimic the role of putrescine in the human enzyme. In the potato enzyme, the positively charged residues form an extensive network of hydrogen bonds bridging a cluster of highly conserved negatively charged residues and the active site, including interactions with the catalytic residues Glu16 and His249. The results explain the constitutively high activity of plant S-adenosylmethionine decarboxylases in the absence of putrescine and are consistent with previously proposed models for how putrescine together with the buried, negatively charged site regulates enzyme activity.

1MHM is a [http://en.wikipedia.org/wiki/Protein_complex Protein complex] structure of sequences from [http://en.wikipedia.org/wiki/Solanum_tuberosum Solanum tuberosum]. Active as [http://en.wikipedia.org/wiki/Adenosylmethionine_decarboxylase Adenosylmethionine decarboxylase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=4.1.1.50 4.1.1.50] Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1MHM OCA].  

[[Category: Bennett, E M.]]

[[Category: Ealick, S E.]]

[[Category: Ekstrom, J L.]]

[[Category: Pegg, A E.]]

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