title: Evolutionary relationships between heme-binding ferredoxin α + β barrels.
abstract: BACKGROUND
  The α + β barrel superfamily of the ferredoxin-like fold consists of a functionally diverse group of evolutionarily related proteins. The barrel architecture of these proteins is formed by either homo-/hetero-dimerization or duplication and fusion of ferredoxin-like domains. Several members of this superfamily bind heme in order to carry out their functions.
  
  
  RESULTS
  We analyze the heme-binding sites in these proteins as well as their barrel topologies. Our comparative structural analysis of these heme-binding barrels reveals two distinct modes of packing of the ferredoxin-like domains to constitute the α + β barrel, which is typified by the Type-1/IsdG-like and Type-2/OxdA-like proteins, respectively. We examine the heme-binding pockets and explore the versatility of the α + β barrels ability to accommodate heme or heme-related moieties, such as siroheme, in at least three different sites, namely, the mode seen in IsdG/OxdA, Cld/DyP/EfeB/HemQ and siroheme decarboxylase barrels.
  
  
  CONCLUSIONS
  Our study offers insights into the plausible evolutionary relationships between the two distinct barrel packing topologies and relate the observed heme-binding sites to these topologies.
authors.affiliation: CSIR-Institute of Microbial Technology (IMTECH), Sector 39-A, Chandigarh, India.
authors.forename: Giriraj
authors.initials: G
authors.lastname: Acharya
authors.affiliation: CSIR-Institute of Microbial Technology (IMTECH), Sector 39-A, Chandigarh, India.
authors.forename: Gurmeet
authors.initials: G
authors.lastname: Kaur
authors.affiliation: CSIR-Institute of Microbial Technology (IMTECH), Sector 39-A, Chandigarh, India. krishna@imtech.res.in.
authors.forename: Srikrishna
authors.initials: S
authors.lastname: Subramanian
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics; D019143:Evolution, Molecular; D005288:Ferredoxins / Q000737:chemistry* / Q000235:genetics; D006418:Heme / Q000031:analogs & derivatives / Q000737:chemistry / Q000235:genetics; D008958:Models, Molecular; D055503:Protein Multimerization; D017433:Protein Structure, Secondary
chemical_list: D002352:Carrier Proteins; D005288:Ferredoxins; D006418:Heme; C009272:siroheme
keywords: Barrel packing; Heme; Hemoprotein; Iron metabolism; Protein evolution