Catalytic inhibition of human DNA topoisomerase IIalpha by hypericin, a naphthodianthrone from St. John's wort (Hypericum perforatum).

St. John's wort (Hypericum perforatum) is the most widely used herbal medicine for the treatment of depression. However, concerns have arisen about the potential of its interaction with other drugs due to the induction of cytochrome P450 isozymes 1A2 and 3A4 by the components hypericin and hyperforin, respectively. Structurally similar natural products are often employed as antitumor agents due to their action as inhibitors of DNA topoisomerases, nuclear enzymes that modify DNA during cellular proliferation. Preliminary findings that hypericin inhibited the DNA relaxation activity of topoisomerase IIalpha (topo II; EC 5.99.1.3) led us to investigate the mechanism of enzyme inhibition. Rather than stabilizing the enzyme in covalent complexes with DNA (cleavage complexes), hypericin inhibited the enzyme prior to DNA cleavage. In vitro assays indicate that hypericin is a potent antagonist of cleavage complex stabilization by the chemotherapeutics etoposide and amsacrine. This antagonism appears to be due to the ability of hypericin to intercalate or distort DNA structure, thereby precluding topo II binding and/or DNA cleavage. Supporting its non-DNA damaging, catalytic inhibition of topo II, hypericin was shown to be equitoxic to both wild-type and amsacrine-resistant HL-60 leukemia cell lines. Moreover, hypericin was incapable of stimulating DNA damage-responsive gene promoters that are activated by etoposide. As with the in vitro topo II assay, antagonism of DNA damage stimulated by 30 microM etoposide was evident in leukemia cells pretreated with 5 microM hypericin. Since many cancer patients experience clinical depression and concomitantly self-medicate with herbal remedies, extracts of St. John's wort should be investigated further for their potential to antagonize topo II-directed chemotherapy regimens.

Core structure of the envelope glycoprotein GP2 from Ebola virus at 1.9-A resolution.

Ebola virions contain a surface transmembrane glycoprotein (GP) that is responsible for binding to target cells and subsequent fusion of the viral and host-cell membranes. GP is expressed as a single-chain precursor that is posttranslationally processed into the disulfide-linked fragments GP1 and GP2. The GP2 subunit is thought to mediate membrane fusion. A soluble fragment of the GP2 ectodomain, lacking the fusion-peptide region and the transmembrane helix, folds into a stable, highly helical structure in aqueous solution. Limited proteolysis studies identify a stable core of the GP2 ectodomain. This 74-residue core, denoted Ebo-74, was crystallized, and its x-ray structure was determined at 1.9-A resolution. Ebo-74 forms a trimer in which a long, central three-stranded coiled coil is surrounded by shorter C-terminal helices that are packed in an antiparallel orientation into hydrophobic grooves on the surface of the coiled coil. Our results confirm the previously anticipated structural similarity between the Ebola GP2 ectodomain and the core of the transmembrane subunit from oncogenic retroviruses. The Ebo-74 structure likely represents the fusion-active conformation of the protein, and its overall architecture resembles several other viral membrane-fusion proteins, including those from HIV and influenza.

An assessment of treatment outcome in American Board of Orthodontics cases.

In a retrospective study, 90 American Board of Orthodontic (ABO) cases were evaluated for treatment outcome. Changes in occlusion, cephalometric skeletal and dental variables, soft tissue variables, and root resorption were evaluated. The occlusions of completed ABO cases were compared with 147 naturally occurring good-to-excellent occlusions from the Andrews Foundation for Education and Research, using the Ideal Tooth Relationship Index (ITRI). Cephalometric variables were evaluated in relation to an "acceptable range" based on established standards. Photographs were evaluated for lip posture at rest and at closure, and the incidence and the severity of root resorption of maxillary and mandibular teeth excluding second molars were evaluated from panoramic radiographs. After treatment, occlusions of ABO cases scored significantly higher overall and for all ITRI segments except the anterior interarch segment when compared with Andrew's sample. In all the ABO cases, ideal overjet and overbite were attained. Cephalometrically, the mandibular plane and the Y-axis angle showed no significant change as a result of treatment. However, skeletal dysplasia (ANB) and skeletal convexity (Na-A-Po) showed improvement. Dentally, the maxillary incisor position and inclination, the interincisal angle, and the lower incisor position ended within the acceptable range, whereas the lower incisors were proclined. Soft tissue variables also improved, lip balance and harmony, closure at rest, and closure without strain all improved. The nasolabial angle showed little change. Most of the root resorption was minor in nature and involved the maxillary and mandibular central and lateral incisors. In conclusion, the ABO cases were well treated and showed marked improvement in occlusion, cephalometric, and soft tissue changes, although experiencing minor iatrogenic effects.