The catalytic power of magnesium chelatase: a benchmark for the AAA+ ATPases

• Published in: FEBS letters Vol. 590; no. 12; pp. 1687 - 1693
• Main Authors: Adams, Nathan B. P., Brindley, Amanda A., Hunter, C. Neil, Reid, James D.
• Format: Journal Article
• Language: English
• Published: England John Wiley and Sons Inc 01-06-2016
• Subjects: Adenosine Triphosphatases - chemistry; Adenosine Triphosphatases - metabolism; Adenosine Triphosphate - chemistry; Adenosine Triphosphate - metabolism; ATP hydrolysis; ATPases associated with various cellular activities (AAA) magnesium protoporphyrin IX; Catalysis; chelatase; chlorophyll biosynthesis; Gun4; Lyases - chemistry; Lyases - metabolism; Magnesium - chemistry; Magnesium - metabolism; Protoporphyrins - biosynthesis; Protoporphyrins - chemistry; Research Letter; Research Letters; Synechocystis - enzymology; ATPases associated with various cellular activities (AAA) magnesium protoporphyrin IX; chelatase; ATP hydrolysis; chlorophyll biosynthesis; Gun4
• ISSN: 0014-5793; 1873-3468
• DOI: 10.1002/1873-3468.12214

In the first committed reaction of chlorophyll biosynthesis, magnesium chelatase couples ATP hydrolysis to the thermodynamically unfavorable Mg2+ 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 × 106 m) and a catalytic rate enhancement, kcat/KmDIXK0.5Mgkuncat, of 30 × 1015 m−1, increasing to 300 × 1015 m−1 with the activator protein Gun4. This is the first demonstration of the thermodynamic benefit of ATP hydrolysis in the AAA+ family.