Biology Reference
In-Depth Information
infection by the Ebola and SARS-CoV pseudotypes, respectively. In addition,
the thiocarbazate inhibited
in vitro
propagation of malaria parasite
Plasmodium
falciparum
., 2008).
Finally, another natural entry inhibitor is provided by monoclonal
neutralizing antibodies. Many monoclonal antibodies can be isolated from
immortalized B-cells recovered from patients or from mice hybridomas following
immunization. The antibodies can be selected by ELISA assay using soluble
envelope proteins or pseudoparticles. The neutralizing potential of these anti-
bodies can be easily screened using pseudoparticles with high-throughput infec-
tion assays, and the inhibitory effect can be verified with replicating viruses.
In the case of HCV, using an antibody antigen-binding fragment phagedisplay
library generated from a donor chronically infected with HCV, of 115 clones
showing specific binding to HCV E2 glycoprotein, 5 monoclonal antibodies
presented neutralizing activities against cell-culture HCV (HCVcc), JFH-1
virus, and a panel of HCVpp displaying E1-E2 from diverse genotypes (Law
et al
and inhibited
Leishmania
major (Shah
et al
., 2008). Overall, neutralizing antibodies can inhibit the different steps of the
entry process from binding to membrane fusion by targeting the domains
involved in this step or by limiting the conformational changes of the envelope
complex. Interestingly, one study has recently highlighted the feasibility of
targeting short-lived envelope glycoprotein intermediates for inhibition of mem-
brane fusion using monoclonal antibodies (York
., 2010). This action is very
similar to the peptides against HIV membrane fusion on the market. Such
strategies to effectively target fusion peptide function in the endosome may
lead to the discovery of novel classes of antiviral agents, and screens using
pseudoparticles will provide an easily wielded system to identify such infrequent
antibodies.
et al
V. CONCLUSIONS
All viruses have developed varied mechanisms to reach the same goal. They vary
greatly in structure, but all seem to have a common mechanism of action, in
which a ligand-triggered large-scale conformational change in the fusion protein
is coupled to apposition and merger of the two bilayers. In spite of the different
mechanisms to activate the fusion peptide, fusion proteins are distributed into
three classes based on their structural homologies. Future experiments must aim
to elucidate the molecular mechanisms and the dynamics of the conformational
changes driving virus entry. This will require the development of new
approaches to study the rapid conformational changes of a small number of
membrane interacting protein molecules and domains. A more realistic goal is
the determination of all the structures of proteins that mediate the entry of all
human viruses, either at a prebinding or postfusion stage.
