Stabilization of poliovirus by capsid-binding antiviral drugs is due to entropic effects.

When poliovirus attaches to its receptor or is heated in hypotonic buffers, the virion undergoes an irreversible conformational transition from the native 160 S (or N) particle to the 135 S (or A) particle, which is believed to mediate cell entry. The first-order rate constants for the thermally induced transition have been measured as a function of temperature for virus alone and for complexes of the virus with capsid-binding drugs that inhibit the receptor and thermally mediated conversion. Although the drugs have minimum inhibitory concentrations (MIC) that differ by almost three orders of magnitude, the activation energies for the N to A transition for the drug complexes (145 kcal/mol) were indistinguishable from each other or from that of the virus alone. We conclude that the antiviral activity of these drugs derives from a novel mechanism in which drug-binding stabilizes the virions through entropic effects.

A structurally biased combinatorial approach for discovering new anti-picornaviral compounds.

BACKGROUND: Picornaviruses comprise a family of small, non-enveloped RNA viruses. A common feature amongst many picornaviruses is a hydrophobic pocket in the core of VP1, one of the viral capsid proteins. The pocket is normally occupied by a mixture of unidentified, fatty acid-like moieties, which can be competed out by a family of capsid-binding, antiviral compounds. Many members of the Picornaviridae family are pathogenic to both humans and livestock, yet no adequate therapeutics exist despite over a decade's worth of research in the field. To address this challenge, we developed a strategy for rapid identification of capsid-binding anti-picornaviral ligands. The approach we took involved synthesizing structurally biased combinatorial libraries that had been targeted to the VP1 pocket of poliovirus and rhinovirus. The libraries are screened for candidate ligands with a high throughput mass spectrometry assay. RESULTS: Using the mass spectrometry assay, we were able to identify eight compounds from a targeted library of 75 compounds. The antiviral activity of these candidates was assessed by (i) measuring the effect on the kinetics of viral uncoating and (ii) the protective effect of each drug in traditional cell-based assays. All eight of the candidates exhibited antiviral activity, but three of them were particularly effective against poliovirus and rhinovirus. CONCLUSIONS: The results illustrate the utility of combining structure-based design with combinatorial chemistry. The success of our approach suggests that assessment of small, targeted libraries, which query specific chemical properties, may be the best strategy for surveying all of chemical space for ideal anti-picornaviral compounds.

Thyroid hemiagenesis accompanying a thyroglossal duct cyst: a case report.

A case of thyroid hemiagenesis discovered incidentally in a patient presenting with a thyroglossal duct cyst is reported. Thyroid embryology is briefly reviewed. Various characteristics of thyroid hemiagenesis and thyroglossal duct cysts are explored.

Reliability and factor structure of the Chinese GHQ-30 for parents with preschool mentally handicapped children.

The Chinese version of the General Health Questionnaire (GHQ-30) was administered to 381 parents of preschool mentally handicapped children, along with other instruments that assessed their stress, mental health, coping styles, and care-giving patterns. The GHQ-30 was found to have high internal consistency as a scale and high item-total correlations for most of the items. Factor analysis with a four-factor solution showed that four factors were abstracted from the scale, namely, anxiety, depression, interpersonal dysfunctioning, and inadequate coping. It also was found that the factors extracted could be reproduced reliably in two random subsamples and that the factor structure derived from the present sample corresponds to the previously reported data on the dimensionality of the Chinese GHQ-30.

Use of MCSS to design small targeted libraries: application to picornavirus ligands.

Computational methods were used to design structure-based combinatorial libraries of antipicornaviral capsid-binding ligands. The multiple copy simultaneous search (MCSS) program was employed to calculate functionality maps for many diverse functional groups for both the poliovirus and rhinovirus capsid structures in the region of the known drug binding pocket. Based on the results of the MCSS calculations, small combinatorial libraries consisting of 10s or 100s of three-monomer compounds were designed and synthesized. Ligand binding was demonstrated by a noncell-based mass spectrometric assay, a functional immuno-precipitation assay, and crystallographic analysis of the complexes of the virus with two of the candidate ligands. The P1/Mahoney poliovirus strain was used in the experimental studies. A comparison showed that the MCSS calculations had correctly identified the observed binding site for all three monomer units in one ligand and for two out of three in the other ligand. The correct central monomer position in the second ligand was reproduced in calculations in which the several key residues lining the pocket were allowed to move. This study validates the computational methodology. It also illustrates that subtle changes in protein structure can lead to differences in docking results and points to the importance of including target flexibility, as well as ligand flexibility, in the design process.

Kinetic analysis of the effect of poliovirus receptor on viral uncoating: the receptor as a catalyst.

We examined the role of soluble poliovirus receptor on the transition of native poliovirus (160S or N particle) to an infectious intermediate (135S or A particle). The viral receptor behaves as a classic transition state theory catalyst, facilitating the N-to-A conversion by lowering the activation energy for the process by 50 kcal/mol. In contrast to earlier studies which demonstrated that capsid-binding drugs inhibit thermally mediated N-to-A conversion through entropic stabilization alone, capsid-binding drugs are shown to inhibit receptor-mediated N-to-A conversion through a combination of enthalpic and entropic effects.

Molecular tectonic model of virus structural transitions: the putative cell entry states of poliovirus.

Upon interacting with its receptor, poliovirus undergoes conformational changes that are implicated in cell entry, including the externalization of the viral protein VP4 and the N terminus of VP1. We have determined the structures of native virions and of two putative cell entry intermediates, the 135S and 80S particles, at approximately 22-A resolution by cryo-electron microscopy. The 135S and 80S particles are both approximately 4% larger than the virion. Pseudoatomic models were constructed by adjusting the beta-barrel domains of the three capsid proteins VP1, VP2, and VP3 from their known positions in the virion to fit the 135S and 80S reconstructions. Domain movements of up to 9 A were detected, analogous to the shifting of tectonic plates. These movements create gaps between adjacent subunits. The gaps at the sites where VP1, VP2, and VP3 subunits meet are plausible candidates for the emergence of VP4 and the N terminus of VP1. The implications of these observations are discussed for models in which the externalized components form a transmembrane pore through which viral RNA enters the infected cell.