title: An ancestral nuclear protein assembly: crystal structure of the Methanopyrus kandleri histone.
abstract: Eukaryotic histone proteins condense DNA into compact structures called nucleosomes. Nucleosomes were viewed as a distinguishing feature of eukaryotes prior to identification of histone orthologs in methanogens. Although evolutionarily distinct from methanogens, the methane-producing hyperthermophile Methanopyrus kandleri produces a novel, 154-residue histone (HMk). Amino acid sequence comparisons show that HMk differs from both methanogenic and eukaryotic histones, in that it contains two histone-fold ms within a single chain. The two HMk histone-fold ms, N and C terminal, are 28% identical in amino acid sequence to each other and approximately 21% identical in amino acid sequence to other histone proteins. Here we present the 1.37-A-resolution crystal structure of HMk and report that the HMk monomer structure is homologous to the eukaryotic histone heterodimers. In the crystal, HMk forms a dimer homologous to [H3-H4](2) in the eukaryotic nucleosome. Based on the spatial similarities to structural ms found in the eukaryotic nucleosome that are important for DNA-binding, we infer that the Methanopyrus histone binds DNA in a manner similar to the eukaryotic histone tetramer [H3-H4](2).
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1570, USA.
authors.forename: R L
authors.initials: RL
authors.lastname: Fahrner
authors.forename: D
authors.initials: D
authors.lastname: Cascio
authors.forename: J A
authors.initials: JA
authors.lastname: Lake
authors.forename: A
authors.initials: A
authors.lastname: Slesarev
mesh_terms: D000595:Amino Acid Sequence; D019843:Archaeal Proteins / Q000737:chemistry* / Q000378:metabolism; D019295:Computational Biology; D018360:Crystallography, X-Ray; D004247:DNA / Q000378:metabolism; D019605:Euryarchaeota / Q000737:chemistry*; D006657:Histones / Q000737:chemistry* / Q000378:metabolism; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid
chemical_list: D019843:Archaeal Proteins; D006657:Histones; D009687:Nuclear Proteins; D004247:DNA