Emergence of avian origin and equine origin canine influenza viruses (CIVs) in Asia and the United States brings important concerns. Humans are in closer and more frequent contact with dogs than other common hosts of influenza. Thus, CIV is a potential threat to human health. However, little is known about the determinants of CIV host tropism or the transmissibility of CIVs to humans. An amino acid change (W222L) was implicated in modifying hemagglutinin receptor binding by CIV. This was tested using reverse genetics, glycan microarray and virus histochemistry. Glycan microarray demonstrated that avian-origin CIV (H3N2-222W) bind predominantly to alpha-2, 3 linked glycans. Virus histochemistry indicated that rH3N2-222L had higher binding affinity with epithelial cilia of canine tracheal tissue and weaker binding with avian tracheal tissue. Ferret infection demonstrated that the avian-origin H3N2 CIV could cause infection and limited to rhinitis, suggesting that CIV could infect humans.

<p> This study addresses the issue of how to convert peptides into drug-like non-peptides while retaining the biological activity at peptide receptors. Angiotensin II (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe, Ang II) was used as a model peptide.</p><p> Small bioactive peptides are in most cases conformationally flexible molecules. Rigidified peptide analogues or peptidomimetic scaffolds can be introduced into the peptide, to enforce a particular backbone conformation, and thereby locate the side-chains at defined positions in space. The conformationally constrained analogues are of considerable value in determining biologically active conformation(s) of the studied peptide. The strategy applied in this thesis includes identification of non-pharmacophoric amino acid residues, rigidification, conformational analysis and incorporation of turn mimicking scaffolds in </p><p>Ang II. Several side-chain cyclized (disulfide and methylendithioether) Ang II analogues have been synthesized. The binding studies of the rigidified analogues demonstrated that the compounds designed for the AT₁-receptor had affinity for both receptor subtypes, while the compounds designed for the AT₂-receptor displayed high selectivity only for this receptor subtype. Conformational evaluation revealed that several of the cyclized Ang II analogues most probably adopt a <i>γ</i>-turn like conformation around Tyr-4 while interacting with the </p><p>Ang II receptor. Based on this hypothesis, three different <i>γ</i>-turn mimetics replacing amino acid residues 3-5 were designed, synthesized and incorporated into Ang II. One of the synthesized pseudopeptides, incorporating an azepine-containing <i>γ</i>-turn mimetic, exerted high binding affinity and agonistic activity. These results strongly support the theory that Ang II adopts a <i>γ</i>-turn like conformation when activating the AT₁ receptor. The other Ang II analogues, incorporating bicyclic and aromatic <i>γ</i>-turn mimetics, did not display any binding to the AT₁ receptor.</p>

This study addresses the issue of how to convert peptides into drug-like non-peptides while retaining the biological activity at peptide receptors. Angiotensin II (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe, Ang II) was used as a model peptide. Small bioactive peptides are in most cases conformationally flexible molecules. Rigidified peptide analogues or peptidomimetic scaffolds can be introduced into the peptide, to enforce a particular backbone conformation, and thereby locate the side-chains at defined positions in space. The conformationally constrained analogues are of considerable value in determining biologically active conformation(s) of the studied peptide. The strategy applied in this thesis includes identification of non-pharmacophoric amino acid residues, rigidification, conformational analysis and incorporation of turn mimicking scaffolds in Ang II. Several side-chain cyclized (disulfide and methylendithioether) Ang II analogues have been synthesized. The binding studies of the rigidified analogues demonstrated that the compounds designed for the AT1-receptor had affinity for both receptor subtypes, while the compounds designed for the AT2-receptor displayed high selectivity only for this receptor subtype. Conformational evaluation revealed that several of the cyclized Ang II analogues most probably adopt a γ-turn like conformation around Tyr-4 while interacting with the Ang II receptor. Based on this hypothesis, three different γ-turn mimetics replacing amino acid residues 3-5 were designed, synthesized and incorporated into Ang II. One of the synthesized pseudopeptides, incorporating an azepine-containing γ-turn mimetic, exerted high binding affinity and agonistic activity. These results strongly support the theory that Ang II adopts a γ-turn like conformation when activating the AT1 receptor. The other Ang II analogues, incorporating bicyclic and aromatic γ-turn mimetics, did not display any binding to the AT1 receptor.