title: The crystal structure of Aq_328 from the hyperthermophilic bacteria Aquifex aeolicus shows an ancestral histone fold.
abstract: The structure of Aq_328, an uncharacterized protein from hyperthermophilic bacteria Aquifex aeolicus, has been determined to 1.9 A by using multi-wavelength anomalous diffraction (MAD) phasing. Although the amino acid sequence analysis shows that Aq_328 has no significant similarity to proteins with a known structure and function, the structure comparison by using the Dali server reveals that it: (1) assumes a histone-like fold, and (2) is similar to an ancestral nuclear histone protein (PDB code 1F1E) with z-score 8.1 and RMSD 3.6 A over 124 residues. A sedimentation equilibrium experiment indicates that Aq_328 is a monomer in solution, with an average sedimentation coefficient of 2.4 and an apparent molecular weight of about 20 kDa. The overall architecture of Aq_328 consists of two noncanonical histone domains in tandem repeat within a single chain, and is similar to eukaryotic heterodimer (H2A/H2B and H3/H4) and an archaeal histone heterodimer (HMfA/HMfB). The sequence comparisons between the two histone domains of Aq_328 and six eukaryotic/archaeal histones demonstrate that most of the conserved residues that underlie the Aq_328 architecture are used to build and stabilize the two cross-shaped antiparallel histone domains. The high percentage of salt bridges in the structure could be a factor in the protein's thermostability. The structural similarities to other histone-like proteins, molecular properties, and potential function of Aq_328 are discussed in this paper.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Yang
authors.initials: Y
authors.lastname: Qiu
authors.forename: Valentina
authors.initials: V
authors.lastname: Tereshko
authors.forename: Youngchang
authors.initials: Y
authors.lastname: Kim
authors.forename: Rongguang
authors.initials: R
authors.lastname: Zhang
authors.forename: Frank
authors.initials: F
authors.lastname: Collart
authors.forename: Mohammed
authors.initials: M
authors.lastname: Yousef
authors.forename: Anthony
authors.initials: A
authors.lastname: Kossiakoff
authors.forename: Andrzej
authors.initials: A
authors.lastname: Joachimiak
mesh_terms: D001419:Bacteria / Q000737:chemistry / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D003001:Cloning, Molecular; D003460:Crystallization; D003461:Crystallography; D004926:Escherichia coli / Q000235:genetics; D006657:Histones / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D017510:Protein Folding; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D006657:Histones; D011994:Recombinant Proteins