No abstract

Channel-forming colicins are bacterial toxins that spontaneously insert into the inner cell membrane of sensitive bacteria to form voltage-gated ion channels. It has been shown that the channel current and the conformational flexibility of colicin E1 channel domain depend on the membrane surface potential, which is regulated by the anionic lipid content and the ion concentration. To better understand the dependence of colicin structure and dynamics on the membrane surface potential, we have used solid-state NMR to investigate the topology and segmental motion of the closed state of colicin Ia channel-forming domain in membranes of different anionic lipid contents and ion concentrations. Colicin Ia channel domain was reconstituted into membranes with different POPG and KCl concentrations. 1H spin diffusion experiments indicate that the protein contains a small domain that inserts into the hydrophobic center of the 70% anionic membrane, similar to when it binds to the 25% anionic membrane. Measurements of C-H and N-H dipolar couplings indicate that, on the sub-microsecond time scale, the protein has the least segmental mobility under the high-salt and low-anionic lipid condition, which has the most physiological membrane surface potential. Measurement of millisecond time scale motions yielded similar results. These suggest that optimal channel activity requires the protein to have sufficient segmental rigidity so that entire helices can undergo cooperative conformational motions that are required for translocating the channel-forming helices across the lipid bilayer upon voltage activation.

MiR-34a promotes the apoptosis of HLE-B3 cells by down-regulating Bcl-2 and SIRT1, suggesting that miR-34a may involve in the pathogenesis of cataract formation and targeting miR-34a may be a potentially therapeutic approach for treatment of cataract.

The proposed strategies present statistical evidence of its diagnostic performance and can be used to aid TCM physicians in making single pattern diagnosis according to Zang-Fu theory.