title: One protein, two enzymes revisited: a structural entropy switch interconverts the two isoforms of acireductone dioxygenase.
abstract: Acireductone dioxygenase (ARD) catalyzes different reactions between O2 and 1,2-dihydroxy-3-oxo-5-(methylthio)pent-1-ene (acireductone) depending upon the metal bound in the active site. Ni2+ -ARD cleaves acireductone to formate, CO and methylthiopropionate. If Fe2+ is bound (ARD'), the same substrates yield methylthioketobutyrate and formate. The two forms differ in structure, and are chromatographically separable. Paramagnetism of Fe2+ renders the active site of ARD' inaccessible to standard NMR methods. The structure of ARD' has been determined using Fe2+ binding parameters determined by X-ray absorption spectroscopy and NMR restraints from H98S ARD, a metal-free diamagnetic protein that is isostructural with ARD'. ARD' retains the beta-sandwich fold of ARD, but a structural entropy switch increases order at one end of a two-helix system that bisects the beta-sandwich and decreases order at the other upon interconversion of ARD and ARD', causing loss of the C-terminal helix in ARD' and rearrangements of residues involved in substrate orientation in the active site.
authors.affiliation: Department of Chemistry, Brandeis University, MS 015, Waltham, MA 02454-9110, USA.
authors.forename: Tingting
authors.initials: T
authors.lastname: Ju
authors.forename: Rachel Beaulieu
authors.initials: RB
authors.lastname: Goldsmith
authors.forename: Sergio C
authors.initials: SC
authors.lastname: Chai
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Maroney
authors.forename: Susan Sondej
authors.initials: SS
authors.lastname: Pochapsky
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Pochapsky
mesh_terms: D001665:Binding Sites; D017124:Conserved Sequence; D049308:Dioxygenases / Q000737:chemistry* / Q000378:metabolism*; D019277:Entropy; D007501:Iron / Q000378:metabolism; D007527:Isoenzymes / Q000737:chemistry / Q000378:metabolism; D007709:Klebsiella / Q000201:enzymology*; D008954:Models, Biological; D050505:Mutant Proteins / Q000737:chemistry; D010455:Peptides / Q000737:chemistry; D017433:Protein Structure, Secondary; D013237:Stereoisomerism; D013329:Structure-Activity Relationship
chemical_list: D007527:Isoenzymes; D050505:Mutant Proteins; D010455:Peptides; D007501:Iron; D049308:Dioxygenases; C083734:aci-reductone oxidase (CO-forming)