EF-hand like Region in the N-terminus of Anoctamin 1 Modulates Channel Activity by Ca²⁺ and Voltage

Anoctamin1 (ANO1) also known as TMEM16A is a transmembrane protein that functions as a Ca²⁺ activated chloride channel. Recently, the structure determination of a fungal Nectria haematococca TMEM16 (nhTMEM16) scramblase by X-ray crystallography and a mouse ANO1 by cryo-electron microscopy has provided the insight in molecular architecture underlying phospholipid scrambling and Ca²⁺ binding. Because the Ca²⁺ binding motif is embedded inside channel protein according to defined structure, it is still unclear how intracellular Ca²⁺ moves to its deep binding pocket effectively. Here we show that EF-hand like region containing multiple acidic amino acids at the N-terminus of ANO1 is a putative site regulating the activity of ANO1 by Ca²⁺ and voltage. The EF-hand like region of ANO1 is highly homologous to the canonical EF hand loop in calmodulin that contains acidic residues in key Ca²⁺-coordinating positions in the canonical EF hand. Indeed, deletion and Ala-substituted mutation of this region resulted in a significant reduction in the response to Ca²⁺ and changes in its key biophysical properties evoked by voltage pulses. Furthermore, only ANO1 and ANO2, and not the other TMEM16 isoforms, contain the EF-hand like region and are activated by Ca²⁺. Moreover, the molecular modeling analysis supports that EF-hand like region could play a key role during Ca²⁺ transfer. Therefore, these findings suggest that EF-hand like region in ANO1 coordinates with Ca²⁺ and modulate the activation by Ca²⁺ and voltage.

Effect of pH on weakly acidic and basic model drugs and determination of their ex vivo transdermal permeation routes

ABSTRACT The aim of the present study was to investigate the effect of donor pH on the transdermal permeability of the model drugs across rat skin and also to determine the major route of transport of the drugs. Weakly acidic drugs (partition coefficient) ibuprofen (3.6), aceclofenac (3.9), glipizide (1.9) and weakly basic drugs olanzapine (3.6), telmisartan (6.0), and sildenafil citrate (1.9) were selected for the study. The ex vivo permeation studies of these drugs at different donor pH (pH - 1.2, 4, 5, 6.8, 7.4, and 8) using Franz diffusion cell (area, 7.54 cm2) has shown a pH-dependent permeability. Among these drugs the weakly acidic drugs has shown higher permeation rates compared to the weakly basic drugs. The permeability coefficient and the distribution coefficient of the weakly basic drugs increased on increasing the pH whereas the weakly acidic drugs showed an inverse relation. The weakly basic drugs also showed an increase in permeation with increase in the fraction of unionized species indicating dominance of transcellular route of permeation. With an exception of sildenafil citrate, a weakly basic salt form of the drug which showed a high permeation value at pH 7.4 where 57% of the drug was unionized, indicating the involvement of both paracellular and transcellular route in its permeation.

Essential roles for ID-1 motif of interleukin-4 receptor alpha chain in interleukin-4 signaling / 천식및알레르기

BACKGROUND: Interleukin (IL)-4 is a pleiotropic cytokine that plays an important role in the pathogenesis of the allergic inflammation and asthma. Upon IL-4 receptor (IL-4R) engagement, a variety of signaling mediators, such as JAK kinases and STAT-6 are activated, leading to induction of IL-4 target gene expression including CD23 and germline C epsilon transcription. The function of a membrane-proximal domain of IL-4Ra, termed ID-1, remains to be characterized to date. OBJECTIVE: To assess whether the ID-1 domain mediates the induction of IL-4 target gene expression in a STAT-6-dependent manner. METHODS: The intracellular region of IL-4Ralpha was translationally fused to the extracellular region of IL-2Rbeta to provide ligand specificity to IL-2. Acidic amino acids and serine residues in the ID-1 domain of the chimeric receptor were substituted by site-directed mutagenesis. These receptor cDNAs were stably transfected to M12.4.1 murine B lymphoma cells. Following IL-2 stimulation, wild type and mutant clones for the ID-1 motif were subjected to FACS. RNA blotting and elecroporetic mobility shift assays to address the levels of CD23, germline C epsilon and STAT-6 inductions, respectively. RESULTS: ID-1 mutant clones were defective in gene induction of CD23 and germline C epsilon in response to IL-2 stimulation, as compared with wildtype clones. Moreover, IL-2-mediated STAT-6 activation was abolished in ID-1 mutant clones. CONCLUSION: These results demonstrate that the ID-1 domain of IL-4Ra is essential to induce IL-4 target gene expression through a STAT-6-dependent pathway.