title: In silico functional characterization of a double histone fold domain from the Heliothis zea virus 1.
abstract: BACKGROUND
  Histones are short proteins involved in chromatin packaging; in eukaryotes, two H2a-H2b and H3-H4 histone dimers form the nucleosomal core, which acts as the fundamental DNA-packaging element. The double histone fold is a rare globular protein fold in which two consecutive regions characterized by the typical structure of histones assemble together, thus originating a histone pseudodimer. This fold is included in a few prokaryotic histones and in the regulatory region of guanine nucleotide exchange factors of the Sos family. For the prokaryotic histones, there is no direct structural counterpart in the nucleosomal core particle, while the pseudodimer from Sos proteins is very similar to the dimer formed by histones H2a and H2b.
  
  
  RESULTS
  The absence of a H3-H4-like histone pseudodimer in the available structural databases prompted us to search for proteins that could assume such fold. The application of several secondary structure prediction and fold recognition methods allowed to show that the viral protein gi|22788712 is compatible with the structure of a H3-H4-like histone pseudodimer. Further in silico analyses revealed that this protein module could retain the ability of mediating protein-DNA interactions, and could consequently act as a DNA-binding domain.
  
  
  CONCLUSIONS
  Our results suggest a possible functional role in viral pathogenicity for this novel double histone fold domain; thus, the computational analyses here reported will be helpful in directing future biochemical studies on gi|22788712 protein.
authors.affiliation: Dipartimento di Biotecnologie e Bioscienze, Università degli Studi Milano-Bicocca, P.zza della Scienza 2, 20126 Milan, Italy. claudio.greco@unimib.it
authors.forename: Claudio
authors.initials: C
authors.lastname: Greco
authors.forename: Piercarlo
authors.initials: P
authors.lastname: Fantucci
authors.forename: Luca
authors.initials: L
authors.lastname: De Gioia
mesh_terms: D000465:Algorithms; D000595:Amino Acid Sequence; D002843:Chromatin / Q000737:chemistry; D002868:Chromosomal Proteins, Non-Histone; D019295:Computational Biology / Q000379:methods*; D003198:Computer Simulation; D004247:DNA / Q000737:chemistry; D019281:Dimerization; D006657:Histones / Q000737:chemistry*; D046911:Macromolecular Substances; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D009707:Nucleosomes / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011506:Proteins; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity; D014764:Viral Proteins / Q000737:chemistry*; D014780:Viruses / Q000378:metabolism*
chemical_list: D002843:Chromatin; D002868:Chromosomal Proteins, Non-Histone; D006657:Histones; D046911:Macromolecular Substances; D009687:Nuclear Proteins; D009707:Nucleosomes; D011506:Proteins; D014764:Viral Proteins; D004247:DNA