title: The PRC-barrel: a widespread, conserved domain shared by photosynthetic reaction center subunits and proteins of RNA metabolism.
abstract: BACKGROUND
  The H subunit of the purple bacterial photosynthetic reaction center (PRC-H) is important for the assembly of the photosynthetic reaction center and appears to regulate electron transfer during the reduction of the secondary quinone. It contains a distinct cytoplasmic beta-barrel domain whose fold has no close structural relationship to any other well known beta-barrel domain.
  
  
  RESULTS
  We show that the PRC-H beta-barrel domain is the prototype of a novel superfamily of protein domains, the PRC-barrels, approximately 80 residues long, which is widely represented in bacteria, archaea and plants. This domain is also present at the carboxyl terminus of the pan-bacterial protein RimM, which is involved in ribosomal maturation and processing of 16S rRNA. A family of small proteins conserved in all known euryarchaea are composed entirely of a single stand-alone copy of the domain. Versions of this domain from photosynthetic proteobacteria contain a conserved acidic residue that is thought to regulate the reduction of quinones in the light-induced electron-transfer reaction. Closely related forms containing this acidic residue are also found in several non-photosynthetic bacteria, as well as in cyanobacteria, which have reaction centers with a different organization. We also show that the domain contains several determinants that could mediate specific protein-protein interactions.
  
  
  CONCLUSIONS
  The PRC-barrel is a widespread, ancient domain that appears to have been recruited to a variety of biological systems, ranging from RNA processing to photosynthesis. Identification of this versatile domain in numerous proteins could aid investigation of unexplored aspects of their biology.
authors.affiliation: National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894, USA.
authors.forename: Vivek
authors.initials: V
authors.lastname: Anantharaman
authors.forename: L
authors.initials: L
authors.lastname: Aravind
mesh_terms: D000595:Amino Acid Sequence; D001419:Bacteria / Q000737:chemistry; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D017124:Conserved Sequence / Q000235:genetics / Q000502:physiology*; D030562:Databases, Protein; D019143:Evolution, Molecular; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D008969:Molecular Sequence Data; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics / Q000502:physiology; D021122:Protein Subunits / Q000235:genetics / Q000502:physiology*; D020560:Proteobacteria / Q000737:chemistry; D012329:RNA, Bacterial / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D018909:src Homology Domains / Q000235:genetics / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; D045322:Photosynthetic Reaction Center Complex Proteins; D021122:Protein Subunits; D012329:RNA, Bacterial; D016601:RNA-Binding Proteins