1mhm
Crystal structure of S-adenosylmethionine decarboxylase from potato
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OverviewOverview
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.
About this StructureAbout this Structure
1MHM is a Protein complex structure of sequences from Solanum tuberosum. Active as Adenosylmethionine decarboxylase, with EC number 4.1.1.50 Full crystallographic information is available from OCA.
ReferenceReference
Monomeric S-adenosylmethionine decarboxylase from plants provides an alternative to putrescine stimulation., Bennett EM, Ekstrom JL, Pegg AE, Ealick SE, Biochemistry. 2002 Dec 10;41(49):14509-17. PMID:12463749
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