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We discovered that the hepatitis C virus (HCV) envelope glycoprotein E2 binds to human hepatoma cell lines independently of the previously proposed HCV receptor CD81. Comparative binding studies using recombinant E2 from the most prevalent 1a and 1b genotypes revealed that E2 recognition by hepatoma cells is independent from the viral isolate, while E2–CD81 interaction is isolate specific. Binding of soluble E2 to human hepatoma cells was impaired by deletion of the hypervariable region 1 (HVR1), but the wild‐type phenotype was recovered by introducing a compensatory mutation reported previously to rescue infectivity of an HVR1‐deleted HCV infectious clone. We have identified the receptor responsible for E2 binding to human hepatic cells as the human scavenger receptor class B type I (SR‐BI). E2–SR‐BI interaction is very selective since neither mouse SR‐BI nor the closely related human scavenger receptor CD36, were able to bind E2. Finally, E2 recognition by SR‐BI was competed out in an isolate‐specific manner both on the hepatoma cell line and on the human SR‐BI‐transfected cell line by an anti‐HVR1 monoclonal antibody.

Nipah virus is an emergent paramyxovirus that causes deadly encephalitis and respiratory infections in humans. Two glycoproteins coordinate the infection of host cells, an attachment protein (G), which binds to cell surface receptors, and a fusion (F) protein, which carries out the process of virus-cell membrane fusion. The G protein binds to ephrin B2/3 receptors, inducing G conformational changes that trigger F protein refolding. Using an optical approach based on second harmonic generation, we show that monomeric and dimeric receptors activate distinct conformational changes in G. The monomeric receptor-induced changes are not detected by conformation-sensitive monoclonal antibodies or through electron microscopy analysis of G:ephrinB2 complexes. However, hydrogen/deuterium exchange experiments confirm the second harmonic generation observations and reveal allosteric changes in the G receptor binding and F-activating stalk domains, providing insights into the pathway of receptor-activated virus entry. Nipah virus causes encephalitis in humans. Here the authors use a multidisciplinary approach to study the binding of the viral attachment protein G to its host receptor ephrinB2 and show that monomeric and dimeric receptors activate distinct conformational changes in G and discuss implications for receptor-activated virus entry.

The use of transgenic plants in the production of recombinant proteins for human therapy, including subunit vaccines, is being investigated to evaluate the efficacy and safety of these emerging biopharmaceutical products. We have previously shown that synthesis of recombinant glycoprotein B (gB) of human cytomegalovirus can be targeted to seeds of transgenic tobacco when directed by the rice glutelin 3 promoter, with gB retaining critical features of immunological reactivity (E.S. Tackaberry et al. 1999. Vaccine, 17 : 3020–3029). Here, we report development of second generation transgenic plant lines (T 1 ) homozygous for the transgene. Twenty progeny plants from two lines (A23T 1 -2 and A24T 1 -3) were grown underground in an environmentally contained mine shaft. Based on yields of gB in their seeds, the A23T 1 -2 line was then selected for scale-up in the same facility. Analyses of mature seeds by ELISA showed that gB specific activity in A23T 1 -2 seeds was over 30-fold greater than the best T 0 plants from the same transformation series, representing 1.07% total seed protein. These data demonstrate stable inheritance, an absence of transgene inactivation, and enhanced levels of gB expression in a homozygous second generation plant line. They also provide evidence for the suitability of using this environmentally secure facility to grow transgenic plants producing therapeutic biopharmaceuticals.Key words: transgenic tobacco seeds, homozygous second generation, glycoprotein B, human cytomegalovirus, vaccine, underground mine.