title: The catalytic power of magnesium chelatase: a benchmark for the AAA(+) ATPases.
abstract: In the first committed reaction of chlorophyll biosynthesis, magnesium chelatase couples ATP hydrolysis to the thermodynamically unfavorable Mg(2+) insertion into protoporphyrin IX (ΔG°' of circa 25-33 kJ·mol(-1) ). We explored the thermodynamic constraints on magnesium chelatase and demonstrate the effect of nucleotide hydrolysis on both the reaction kinetics and thermodynamics. The enzyme produces a significant rate enhancement (kcat /kuncat of 400 × 10(6) m) and a catalytic rate enhancement, kcat/KmDIXK0.5Mgkuncat, of 30 × 10(15) m(-1) , increasing to 300 × 10(15) m(-1) with the activator protein Gun4. This is the first demonstration of the thermodynamic benefit of ATP hydrolysis in the AAA(+) family.
authors.affiliation: Department of Molecular Biology and Biotechnology, University of Sheffield, UK.
authors.forename: Nathan B P
authors.identifier: 0000-0003-3080-3448
authors.initials: NB
authors.lastname: Adams
authors.affiliation: Department of Molecular Biology and Biotechnology, University of Sheffield, UK.
authors.forename: Amanda A
authors.initials: AA
authors.lastname: Brindley
authors.affiliation: Department of Molecular Biology and Biotechnology, University of Sheffield, UK.
authors.forename: C Neil
authors.initials: CN
authors.lastname: Hunter
authors.affiliation: Department of Chemistry, University of Sheffield, UK.
authors.forename: James D
authors.initials: JD
authors.lastname: Reid
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000737:chemistry* / Q000378:metabolism; D002384:Catalysis; D008190:Lyases / Q000737:chemistry* / Q000378:metabolism; D008274:Magnesium / Q000737:chemistry* / Q000378:metabolism; D011524:Protoporphyrins / Q000096:biosynthesis / Q000737:chemistry*; D046939:Synechocystis / Q000201:enzymology*
chemical_list: D011524:Protoporphyrins; D000255:Adenosine Triphosphate; C028025:protoporphyrin IX; D000251:Adenosine Triphosphatases; D008190:Lyases; C086788:magnesium chelatase; D008274:Magnesium
keywords: ATP hydrolysis; ATPases associated with various cellular activities (AAA) magnesium protoporphyrin IX; Gun4; chelatase; chlorophyll biosynthesis