Ferritin structure from Mycobacterium tuberculosis: comparative study with homologues identifies extended C-terminus involved in ferroxidase activity

• Published in: PloS one 2011-04, Vol.6 (4), p.e18570-e18570
• Main Authors: Khare, Garima, Gupta, Vibha, Nangpal, Prachi, Gupta, Rakesh K, Sauter, Nicholas K, Tyagi, Anil K
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Amino acids; Analysis; Archaea; Archaeoglobus fulgidus; Automation; Bacteria; Bacterial Proteins - chemistry; Bacterial Proteins - isolation & purification; Bacterial Proteins - metabolism; Bacterioferritin; BASIC BIOLOGICAL SCIENCES; Biochemistry; Biology; C-Terminus; Catalysis; Ceruloplasmin - metabolism; Channel pores; Comparative studies; Conservation; Conserved Sequence; Crystal structure; Crystallography; Crystallography, X-Ray; Cytochrome b Group - chemistry; Cytochrome b Group - isolation & purification; Cytochrome b Group - metabolism; Deoxyribonucleic acid; Detoxification; DNA; electrostatics; Evolution; Ferritin; Ferritins - chemistry; Ferritins - isolation & purification; Ferritins - metabolism; Ferroxidase; fungal structure; Gene expression; Genomes; Homeostasis; Homology; Hydrogen peroxide; Iron; Iron - metabolism; Medicine; Models, Molecular; Molecular Sequence Data; mycobacteria; Mycobacterium smegmatis; Mycobacterium tuberculosis; oxidation; Oxidation-Reduction; Physiology; Prokaryotes; Protein Binding; Protein Denaturation; Protein Stability; Protein structure; Protein Structure, Secondary; Protein Subunits - metabolism; Proteins; Residues; Sequence Alignment; Static Electricity; Structural Homology, Protein; Structure-function relationships; Temperature; Tuberculosis; Virulence; Virulence (Microbiology)
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0018570

Ferritins are recognized as key players in the iron storage and detoxification processes. Iron acquisition in the case of pathogenic bacteria has long been established as an important virulence mechanism. Here, we report a 3.0 Å crystal structure of a ferritin, annotated as Bacterioferritin B (BfrB), from Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis that continues to be one of the world's deadliest diseases. Similar to the other members of ferritin family, the Mtb BfrB subunit exhibits the characteristic fold of a four-helical bundle that possesses the ferroxidase catalytic centre. We compare the structure of Mtb BfrB with representatives of the ferritin family belonging to the archaea, eubacteria and eukarya. Unlike most other ferritins, Mtb BfrB has an extended C-terminus. To dissect the role of this extended C-terminus, truncated Mtb BfrB was purified and biochemical studies implicate this region in ferroxidase activity and iron release in addition to providing stability to the protein. Functionally important regions in a protein of known 3D-structure can be determined by estimating the degree of conservation of the amino-acid sites with its close homologues. Based on the comparative studies, we identify the slowly evolving conserved sites as well as the rapidly evolving variable sites and analyze their role in relation to structure and function of Mtb BfrB. Further, electrostatic computations demonstrate that although the electrostatic environment of catalytic residues is preserved within the family, extensive variability is exhibited by residues defining the channels and pores, in all likelihood keeping up with the diverse functions executed by these ferritins in varied environments.