Immunisation against a serine protease inhibitor reduces intensity of Plasmodium berghei infection in mosquitoes

The mosquito innate immune response is able to clear the majority of Plasmodium parasites. This immune clearance is controlled by a number of regulatory molecules including serine protease inhibitors (serpins). To determine whether such molecules could represent a novel target for a malaria transmission-blocking vaccine, we vaccinated mice with Anopheles gambiae serpin-2. Antibodies against Anopheles gambiae serpin-2 significantly reduced the infection of a heterologous Anopheles species (Anopheles stephensi) by Plasmodium berghei, however this effect was not observed with Plasmodium falciparum. Therefore, this approach of targeting regulatory molecules of the mosquito immune system may represent a novel approach to transmission-blocking malaria vaccines.     

Effect of incorporating a thiophene tail in the scaffold of acetazolamide on the inhibition of human carbonic anhydrase isoforms I,II, IX and XII

The high resolution crystal structure of 5-(2-thienylacetamido)-1,3,4-thiadiazole-2-sulfonamide complexed to human (h) carbonic anhydrase (CA, EC 4.2.1.1) isoform hCA II is reported. The compound binds in a similar manner with acetazolamide when the sulfamoyl–thiadiazolyl–acetamido fragment of the two compounds is considered, but the thienyl tail was positioned in the subpocket 2, rarely observed by other investigated CA inhibitors. This positioning allows interaction with amino acid residues (such as Asn67, Ile91, Gln92 and Val121 which are variable in other isoforms of medicinal chemistry interest, such as hCA I, IX and XII. Indeed, the investigated sulfonamide was a medium potency hCA I and II inhibitor but was highly effective as a hCA IX and XII inhibitor. This different behavior with respect to acetazolamide (a promiscuous inhibitor of all these isoforms) has been explained by resolving the crystal structure, and may be used to design more isoform-selective compounds.     

Development of a pharmacophore model for the catecholamine release-inhibitory peptide catestatin: Virtual screening and functional testing identify novel small molecule therapeutics of hypertension

The endogenous catecholamine release-inhibitory peptide catestatin (CST) regulates events leading to hypertension and cardiovascular disease. Earlier we studied the structure of CST by NMR, molecular modeling, and amino acid scanning mutagenesis. That structure has now been exploited for elucidation of interface pharmacophores that mediate binding of CST to its target, with consequent secretory inhibition. Designed pharmacophore models allowed screening of 3D structural domains. Selected compounds were tested on both cultured catecholaminergic cells and an in vivo model of hypertension; in each case, the candidates showed substantial mimicry of native CST actions, with preserved or enhanced potency and specificity. The approach and compounds have thus enabled rational design of novel drug candidates for treatment of hypertension or autonomic dysfunction.     

Structural study of the location of the phenyl tail of benzene sulfonamides and the effect on human carbonic anhydrase inhibition

The crystal structure of 4-phenylacetamidomethyl-benzenesulfonamide (4ITP) bound to human carbonic anhydrase (hCA, EC 4.2.1.1) II is reported. 4ITP is a medium potency hCA I and II inhibitor (K_Is of 54–75 nM), a strong mitochondrial CA VA/VB inhibitor (K_Is of 8.3–8.6 nM) and a weak transmembrane CA inhibitor (K_Is of 136–212 nM against hCA IX and XII). This elongated compound binds in an extended conformation to hCA II, with its tail lying towards the hydrophobic half of the active site whereas the sulfonamide moiety coordinates the zinc ion. The present structure was compared to that of structurally related aromatic sulfonamides, such as 4-phenylacetamido-benzene-sulfonamide (3OYS), 4-(2-mercaptophenylacetamido)-benzene-sulfonamide (2HD6) and 4-(3-nitrophenyl)-ureido-benzenesulfonamide (3N2P). Homology models of the hCA I, VA, VB, IX and XII structures were build which afforded an understanding of the amino acids involved in the binding of these compounds to these isoforms. The main conclusion of the study is that the orientation of the tail moiety and the presence of flexible linkers as well polar groups in it, strongly influence the potency and the selectivity of the sulfonamides for the inhibition of cytosolic, mitochondrial or transmembrane CA isoforms.     

Characterization of the host-defense peptides from skin secretions of Merlin's clawed frog Pseudhymenochirus merlini: Insights into phylogenetic relationships among the Pipidae

The family Pipidae comprises the genera Hymenochirus, Pipa, Pseudhymenochirus, Silurana, and Xenopus but phylogenetic relationships within the family are unclear. Peptidomic analysis of norepinephrine-stimulated skin secretions from Pseudhymenochirus merlini Chabanaud, 1920, the single species within the genus Pseudhymenochirus, led to identification of 13 host-defense peptides with antimicrobial activity. Two peptides (hymenochirin-1Pa and -1Pb) show structural similarity to hymenochirin-1B from Hymenochirus boettgeri and eight peptides (hymenochirin-5Pa, -5Pb, -5Pc, -5Pd, -5Pe, -5Pf, 5Pg and -5Ph) are structurally similar to each other and to hymenochirin-5B from H. boettgeri. Two peptides differing by a single amino acid (IKIPSFFRNILKKVGKEAVSLM/I AGALKQS), termed pseudhymenochirin-1Pa and -1Pb, and pseudhymenochirin-2Pa (GIFPIFAKLLGKVIKVASSLISKGRTE) do not resemble host-defense peptides previously isolated from pipid frogs. Hymenochirin-5Pe was the most abundant peptide in the secretions and hymenochirin-1Pa the most potent against Staphylococcus aureus (MIC = 2.5 μM) and Escherichia coli (MIC = 10 μM). The data support a close phylogenetic relationship between Hymenochirus and Pseudhymenochirus that is distinct from the Xenopodinae (Xenopus + Silurana) clade with Pipa sister-group to all other extant pipids.     

Effect of Tenofovir on Nucleotidases and Cytokines in HIV-1 Target Cells

Tenofovir (TFV) has been widely used for pre-exposure prophylaxis of HIV-1 infection with mixed results. While the use of TFV in uninfected individuals for prevention of HIV-1 acquisition is actively being investigated, the possible consequences of TFV exposure for the HIV-target cells and the mucosal microenvironment are unknown. In the current study, we evaluated the effects of TFV treatment on blood-derived CD4⁺ T cells, monocyte-derived macrophages and dendritic cells (DC). Purified HIV-target cells were treated with different concentrations of TFV (0.001-1.0 mg/ml) for 2 to 24hr. RNA was isolated and RT-PCR was performed to compare the levels of mRNA expression of nucleotidases and pro-inflammatory cytokine genes (MIP3α, IL-8 and TNFα) in the presence or absence of TFV. We found that TFV increases 5’-ecto-nucleotidase (NT5E) and inhibits mitochondrial nucleotidase (NT5M) gene expression and increases 5’ nucleotidase activity in macrophages. We also observed that TFV stimulates the expression and secretion of IL-8 by macrophages, DC, and activated CD4⁺ T cells and increases the expression and secretion of MIP3α by macrophages. In contrast, TFV had no effect on TNFα secretion from macrophages, DC and CD4⁺ T cells. Our results demonstrate that TFV alters innate immune responses in HIV-target cells with potential implications for increased inflammation at mucosal surfaces. As new preventive trials are designed, these findings should provide a foundation for understanding the effects of TFV on HIV-target cells in microbicide trials.     

Does the position of the electron-donating nitrogen atom in the ring system influence the efficiency of a dye-sensitized solar cell? A computational study

Electronic structure of the XeOF₂ molecule and its two complexes with HX (X= F, Cl, Br, I) molecules have been studied in the gas phase using quantum chemical topology methods: topological analysis of electron localization function (ELF), electron density, ρ(r), reduced gradient of electron density |RDG(r)| in real space, and symmetry adapted perturbation theory (SAPT) in the Hilbert space. The wave function has been approximated by the MP2 and DFT methods, using APF-D, B3LYP, M062X, and B2PLYP functionals, with the dispersion correction as proposed by Grimme (GD3). For the Xe-F and Xe=O bonds in the isolated XeOF₂ molecule, the bonding ELF-localization basins have not been observed. According to the ELF results, these interactions are not of covalent nature with shared electron density. There are two stable F₂OXe^…HF complexes. The first one is stabilized by the F-H^…F and Xe^…F interactions (type I) and the second by the F-H^…O hydrogen bond (type II). The SAPT analysis confirms the electrostatic term, E_elst ⁽¹⁾ and the induction energy, E_ind ⁽²⁾ to be the major contributors to stabilizing both types of complexes.