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KatB, a cyanobacterial Mn-catalase with unique active site configuration: Implications for enzyme function
Subhash C Bihani1, Dhiman Chakravarty2, Anand Ballal2
1Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India.
Free Radical Biology & Medicine
|January 31, 2016
Summary
Manganese catalases (Mn-catalases) are distinct H2O2 detoxifying proteins. This study characterizes KatB from Anabaena PCC7120, revealing its unique active site and hexameric structure, offering insights into Mn-catalase evolution.
Area of Science:
- Biochemistry
- Structural Biology
- Enzymology
Background:
- Manganese catalases (Mn-catalases) detoxify hydrogen peroxide (H2O2) and differ structurally and mechanistically from heme-containing catalases.
- Understanding Mn-catalase active sites is crucial for developing therapeutic catalase mimetics for oxidative stress disorders.
- Structural data on Mn-catalases are limited compared to heme catalases.
Purpose of the Study:
- To biochemically and structurally characterize KatB, a Mn-catalase from the cyanobacterium Anabaena PCC7120.
- To elucidate the active site structure and assembly of KatB.
- To gain insights into the evolutionary relationships within the Ferritin-like superfamily.
Main Methods:
- Over-expression and purification of KatB protein with a C-terminal his-tag in Escherichia coli.
- Biochemical assays to confirm catalase activity and azide inhibition.
- X-ray crystallography to determine the crystal structure of KatB.
Main Results:
- KatB was efficiently produced as a soluble protein in E. coli with Mn(2+) supplementation.
- Purified KatB exhibited efficient catalase activity and relative insensitivity to azide inhibition.
- Crystal structure revealed KatB as a hexamer with a four-helix bundle fold, characteristic of the Ferritin-like superfamily.
- KatB possesses a unique active site with Glu4His2 coordination and two terminal water ligands, distinct from other Mn-catalases but resembling ruberythrin/bacterioferritin active sites.
- The structure supports the classification of Mn-catalases into two distinct groups based on active site configuration.
Conclusions:
- KatB is an efficient Mn-catalase with a unique active site structure and hexameric assembly.
- The findings provide fundamental insights into the evolutionary diversity within the Ferritin-like superfamily.
- This structural characterization advances the understanding of Mn-catalases and their potential for mimetic development.
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