title: KatB, a cyanobacterial Mn-catalase with unique active site configuration: Implications for enzyme function.
abstract: Manganese catalases (Mn-catalases), a class of H2O2 detoxifying proteins, are structurally and mechanistically distinct from the commonly occurring catalases, which contain heme. Active site of Mn-catalases can serve as template for the synthesis of catalase mimetics for therapeutic intervention in oxidative stress related disorders. However, unlike the heme catalases, structural aspects of Mn-catalases remain inadequately explored. The genome of the ancient cyanobacterium Anabaena PCC7120, shows the presence of two Mn-catalases, KatA and KatB. Here, we report the biochemical and structural characterization of KatB. The KatB protein (with a C-terminal his-tag) was over-expressed in Escherichia coli and purified by affinity chromatography. On the addition of Mn(2+) to the E. coli growth medium, a substantial increase in production of the soluble KatB protein was observed. The purified KatB protein was an efficient catalase, which was relatively insensitive to inhibition by azide. Crystal structure of KatB showed a hexameric assembly with four-helix bundle fold, characteristic of the Ferritin-like superfamily. With canonical Glu4His2 coordination geometry and two terminal water ligands, the KatB active site was distinctly different from that of other Mn-catalases. Interestingly, the KatB active site closely resembled the active sites of ruberythrin/bacterioferritin, bi-iron members of the Ferritin-like superfamily. The KatB crystal structure provided fundamental insights into the evolutionary relationship within the Ferritin-like superfamily and further showed that Mn-catalases can be sub-divided into two groups, each with a distinct active site configuration.
authors.affiliation: Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India. Electronic address: scbihani@barc.gov.in.
authors.forename: Subhash C
authors.initials: SC
authors.lastname: Bihani
authors.affiliation: Molecular Biology Division, Bhabha Atomic Research Centre, Mumbai 400085, India; Homi Bhabha National Institute, Anushakti Nagar, Mumbai 400094, India.
authors.forename: Dhiman
authors.initials: D
authors.lastname: Chakravarty
authors.affiliation: Molecular Biology Division, Bhabha Atomic Research Centre, Mumbai 400085, India; Homi Bhabha National Institute, Anushakti Nagar, Mumbai 400094, India. Electronic address: aballal@barc.gov.in.
authors.forename: Anand
authors.initials: A
authors.lastname: Ballal
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D002374:Catalase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D000458:Cyanobacteria / Q000737:chemistry / Q000201:enzymology*; D003573:Cytochrome b Group / Q000737:chemistry*; D004926:Escherichia coli / Q000235:genetics; D005293:Ferritins / Q000737:chemistry*; D015971:Gene Expression Regulation, Enzymologic; D008345:Manganese / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D011487:Protein Conformation; D013329:Structure-Activity Relationship
chemical_list: D001426:Bacterial Proteins; D003573:Cytochrome b Group; D008345:Manganese; D005293:Ferritins; C018032:bacterioferritin; D002374:Catalase
keywords: Catalase; Cyanobacteria; Hydrogen peroxide; Manganese catalase