title: The solution structure of the amino-terminal HHCC domain of HIV-2 integrase: a three-helix bundle stabilized by zinc.
abstract: BACKGROUND
  Integrase mediates a crucial step in the life cycle of the human immunodeficiency virus (HIV). The enzyme cleaves the viral DNA ends in a sequence-dependent manner and couples the newly generated hydroxyl groups to phosphates in the target DNA. Three domains have been identified in HIV integrase: an amino-terminal domain, a central catalytic core and a carboxy-terminal DNA-binding domain. The amino-terminal region is the only domain with unknown structure thus far. This domain, which is known to bind zinc, contains a HHCC motif that is conserved in retroviral integrases. Although the exact function of this domain is unknown, it is required for cleavage and integration.
  
  
  RESULTS
  The three-dimensional structure of the amino-terminal domain of HIV-2 integrase has been determined using two-dimensional and three-dimensional nuclear magnetic resonance data. We obtained 20 final structures, calculated using 693 nuclear Overhauser effects, which display a backbone root-mean square deviation versus the average of 0.25 A for the well defined region. The structure consists of three alpha helices and a helical turn. The zinc is coordinated with His 12 via the N epsilon 2 atom, with His16 via the N delta 1 atom and with the sulfur atoms of Cys40 and Cys43. The alpha helices form a three-helix bundle that is stabilized by this zinc-binding unit. The helical arrangement is similar to that found in the DNA-binding domains of the trp repressor, the prd paired domain and Tc3A transposase.
  
  
  CONCLUSIONS
  The amino-terminal domain of HIV-2 integrase has a remarkable hybrid structure combining features of a three-helix bundle fold with a zinc-binding HHCC motif. This structure shows no similarity with any of the known zinc-finger structures. The strictly conserved residues of the HHCC motif of retroviral integrases are involved in metal coordination, whereas many other well conserved hydrophobic residues are part of the protein core.
authors.affiliation: Bijvoet Center for Biomolecular Research, Utrecht University, The Netherlands.
authors.forename: A P
authors.initials: AP
authors.lastname: Eijkelenboom
authors.forename: F M
authors.initials: FM
authors.lastname: van den Ent
authors.forename: A
authors.initials: A
authors.lastname: Vos
authors.forename: J F
authors.initials: JF
authors.lastname: Doreleijers
authors.forename: K
authors.initials: K
authors.lastname: Hård
authors.forename: T D
authors.initials: TD
authors.lastname: Tullius
authors.forename: R H
authors.initials: RH
authors.lastname: Plasterk
authors.forename: R
authors.initials: R
authors.lastname: Kaptein
authors.forename: R
authors.initials: R
authors.lastname: Boelens
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002712:Chlorides / Q000494:pharmacology; D003545:Cysteine / Q000737:chemistry; D004247:DNA / Q000378:metabolism; D004795:Enzyme Stability; D019427:HIV Integrase / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D006639:Histidine / Q000737:chemistry; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017510:Protein Folding; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D012996:Solutions; D015032:Zinc / Q000737:chemistry*; D017967:Zinc Compounds / Q000494:pharmacology
chemical_list: D002712:Chlorides; D011993:Recombinant Fusion Proteins; D012996:Solutions; D017967:Zinc Compounds; D006639:Histidine; C016837:zinc chloride; D004247:DNA; D019427:HIV Integrase; D015032:Zinc; D003545:Cysteine