Pharmacology and pore-forming domains of the cystic fibrosis transmembrane conductance regulator

The cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride channel member of the ATP-binding cassette (ABC) superfamily of membrane proteins. CFTR has two homologous halves, each consisting of six transmembrane spanning domains (TM) followed by a nucleotide binding fold, connected by a regulatory (R) domain. This thesis addresses the question of which domains are responsible for Cl^- selectivity, i.e., which domains line the channel pore.

To address this question, novel blockers of CFTR were characterized. CFTR was heterologously expressed in Xenopus oocytes to study the mechanism of block by two closely related arylaminobenzoates, diphenylamine-2-carboxylic acid (DPC) and flufenamic acid (FFA). Block by both is voltage-dependent, with a binding site ≈ 40% through the electric field of the membrane. DPC and FFA can both reach their binding site from either side of the membrane to produce a flickering block of CFTR single channels. In addition, DPC block is influenced by Cl^- concentration, and DPC blocks with a bimolecular forward binding rate and a unimolecular dissociation rate. Therefore, DPC and FFA are open-channel blockers of CFTR, and a residue of CFTR whose mutation affects their binding must line the pore.

Screening of site-directed mutants for altered DPC binding affinity reveals that TM-6 and TM-12 line the pore. Mutation of residue 5341 in TM-6 abolishes most DPC block, greatly reduces single-channel conductance, and alters the direction of current rectification. Additional residues are found in TM-6 (K335) and TM-12 (T1134) whose mutations weaken or strengthen DPC block; other mutations move the DPC binding site from TM-6 to TM-12. The strengthened block and lower conductance due to mutation T1134F is quantitated at the single-channel level. The geometry of DPC and of the residues mutated suggest α-helical structures for TM-6 and TM-12. Evidence is presented that the effects of the mutations are due to direct side-chain interaction, and not to allosteric effects propagated through the protein. Mutations are also made in TM-11, including mutation S1118F, which gives voltage-dependent current relaxations. The results may guide future studies on permeation through ABC transporters and through other Cl^- channels.

Argilas pilarizadas: uma tecnologia limpa na reação de isomerização do óxido de estireno

Neste trabalho, fracionou-se e tratou-se a argila Brasgel. Esta argila foi pilarizada em vários estágios de facionamento e/ou tratamento com 5 meq de Al / g de argila: (i) Al-PILC, a argila passou por todos os estágios de fracionamento e tratamento (ARG), (ii) Al-PILCFe, a argila não passou pela etapa de retirada de Fe livre (ARGFe) e (iii) Al-PILCFe/silte, a argila não passou pelas etapas de retirada de silte e Fe livre (ARGFE/silte). Em análise por DRX observou-se que as Al-PILCs apresentaram uma distância basal maior que as argilas de partida. A análise textural indicou que as argilas Al-PILCs e ARGs são materiais mesoporosos, com poros do tipo fenda estreita e do tipo fenda, respectivamente. Além disso, as Al-PILCs apresentaram área superficial razoavelmente maior que as ARGs correspondentes. Outras análises feitas nas argilas foram: teor de Si, Fe e Al; CTC; FTIR; TGA e TGD. As argilas Brasgel pilarizadas foram usadas como catalisador na reação de isomerização do óxido de estireno em hexano sob refluxo. A reação foi seletiva na formação de fenilacetaldeído. As argilas Al-PILCFe e Al-PILCFe/silte apresentaram melhor desempenho catalítico (100 % de conversão em 20 min de reação). Assim, as argilas Brasgel pilarizadas se apresentaram como uma Tecnologia Limpa na reação de isomerização do óxido de estireno ao fenilacetaldeído. Palavras-chave: Desenvolvimento Sustentável. Tecnologia Limpa. Química Verde. Argilas Pilarizadas. Isomerização de Epóxidos.

Surface plasmon resonance transmission filters at 1053 nm based on metallic grating with narrow slit

Metallic gratings with narrow slits can lead to special optical properties such as strongly enhancing the transmission and considerably strengthening the polarized effect. A narrow-band filter suitable for application in optical communication is designed by sandwiching a metallic grating between two identical dielectric films. The maximum transmission can reach 96% after optimizing the parameters of films and grating at a central wavelength of 1053 nm. It is the first time, to our knowledge, that such high transmission has been reported since the discovery of the extraordinarily high transmission through periodic holes or slits; moreover, the extremely polarized effect is also found in P mode of this symmetric grating.