4kp2 | pdb_00004kp2
Crystal structure of homoaconitase large subunit from methanococcus jannaschii (MJ1003)
Structural highlights
FunctionHACA_METJA Hydro-lyase with broad substrate specificity for cis-unsaturated tricarboxylic acids. Catalyzes both the reversible dehydration of (R)-homocitrate ((R)-2-hydroxybutane-1,2,4-tricarboxylate) to produce cis-homoaconitate ((Z)-but-1-ene-1,2,4-tricarboxylate), and its hydration to homoisocitrate ((1R,2S)-1-hydroxybutane-1,2,4-tricarboxylate). Is also able to hydrate the analogous longer chain substrates cis-homo(2)-aconitate, cis-homo(3)-aconitate, and even the non-physiological cis-homo(4)-aconitate with similar efficiency. These reactions are part of the biosynthesis pathway of coenzyme B. Can also catalyze the hydration of maleate to (R)-malate, and that of cis-aconitate. Can not catalyze the hydration of citraconate and the dehydration of (S)-homocitrate, citramalate, 2-isopropylmalate, 3-isopropylmalate, citrate or threo-DL-isocitrate.[1] [2] [3] Publication Abstract from PubMedThe aconitase family of proteins includes three classes of hydro-lyase enzymes: aconitases, homoaconitases and isopropylmalate (IPM) isomerases. They have a common Fe-S cluster-binding site and catalyze the isomerization of specific substrates by sequential dehydration and hydration. The archaeon Methanococcus jannaschii contains two aconitase family proteins, IPM isomerase and homoaconitase, which have 50% sequence identity. These two enzymes are heterodimeric proteins composed of large and small subunits encoded by separate genes. Although structures have been reported for the small subunits of the two enzymes, the first structures of oxidized and reduced forms of the large subunit of IPM isomerase (ox-MJ0499 and red-MJ0499, respectively) from M. jannaschii are reported here at 1.8 and 2.7 A resolution, respectively, together with the structure of the large subunit of homoaconitase (MJ1003) at 2.5 A resolution. The structures of both proteins have unbound Fe-S clusters and contain a fourth cysteine in the active site. The active site of MJ1003 is homologous to that of aconitase, whereas MJ0499 has significant structural distortion at the active site compared with aconitase. In addition, significant large conformational changes were observed in the active site of red-MJ0499 when compared with ox-MJ0499. The active sites of the two proteins adopt two different states before changing to the Fe-S cluster-bound `activated' state observed in aconitase. MJ1003 has an `open' active site, which forms an active pocket for the cluster, while ox-MJ0499 has a `closed' active site, with four cysteines in disulfide bonds. These data will be helpful in understanding the biochemical mechanism of clustering of the Fe-S protein family. Structural characterization and comparison of the large subunits of IPM isomerase and homoaconitase from Methanococcus jannaschii.,Lee EH, Lee K, Hwang KY Acta Crystallogr D Biol Crystallogr. 2014 Apr 1;70(Pt 4):922-31. doi:, 10.1107/S1399004713033762. Epub 2014 Mar 19. PMID:24699638[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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