Evolution of pore structure in microporous silica membranes:sol-gel procedures and strategies

Silica membranes exhibiting excellent molecular sieving capability, which would find applications in fuel‐cell electric vehicles with on‐board hydrogen generation, for example, are the aim of the sol‐gel strategies outlined here. It is shown that optimization of the sol‐gel synthesis parameters is important in order to achieve membranes with minimum defects and hence high selectivity. The preparation of the supported membranes is described and the gas permeation behavior of membranes made from different sol compositions reported

Transfer of rice mitochondrial ribosomal protein L6 gene to the nucleus: acquisition of the 5'-untranslated region via a transposable element

<p>Abstract</p> <p>Background</p> <p>The mitochondria of contemporary organisms contain fewer genes than the ancestral bacteria are predicted to have contained. Because most of the mitochondrial proteins are encoded in the nucleus, the genes would have been transferred from the mitochondrion to the nucleus at some stage of evolution and they must have acquired cis-regulatory elements compatible with eukaryotic gene expression. However, most of such processes remain unknown.</p> <p>Results</p> <p>The ribosomal protein L6 gene (<it>rpl6</it>) has been lost in presently-known angiosperm mitochondrial genomes. We found that each of the two rice <it>rpl6 </it>genes (<it>OsRpl6-1 </it>and <it>OsRpl6-2</it>) has an intron in an identical position within the 5'-untranslated region (UTR), which suggests a duplication of the <it>rpl6 </it>gene after its transfer to the nucleus. Each of the predicted RPL6 proteins lacks an N-terminal extension as a mitochondrial targeting signal. Transient assays using green fluorescent protein indicated that their mature N-terminal coding regions contain the mitochondrial targeting information. Reverse transcription-PCR analysis showed that <it>OsRpl6-2 </it>expresses considerably fewer transcripts than <it>OsRpl6-1</it>. This might be the result of differences in promoter regions because the 5'-noncoding regions of the two <it>rpl6 </it>genes differ at a point close to the center of the intron. There are several sequences homologous to the region around the 5'-UTR of <it>OsRpl6-1 </it>in the rice genome. These sequences have characteristics similar to those of the transposable elements (TE) belonging to the <it>PIF</it>/Harbinger superfamily.</p> <p>Conclusion</p> <p>The above evidences suggest a novel mechanism in which the 5'-UTR of the transferred mitochondrial gene was acquired via a TE. Since the 5'-UTRs and introns within the 5'-UTRs often contain transcriptional and posttranscriptional cis-elements, the transferred rice mitochondrial <it>rpl6 </it>gene may have acquired its cis-element from a TE.</p

Sol-gel synthesis of molecular sieving silica membranes

Polymeric silica sol was synthesized by the acid catalyzed hydrolysis and condensation of tetra-ethyl-ortho-silicate. Calcined unsupported membranes made from this sol showed microporous nature. Supported membranes on alumina were prepared by dipping and calcining. Helium showed activated diffusion with an apparent activation energy of 17 kJ mol−1. H2 permeation was comparable to that of helium under identical conditions. N2, Ar, O2, C3H6, C3H8, n-C4H10 and i-C4H10 permeation values were extremely small and therefore difficult to fit appropriate diffusion models. At 303 K hydrocarbon permeation was about 2 times higher than that of N2, Ar or O2. permselectivity around 1000 and helium permeation in the order of 10−7–10−8 mol m−2 s−1 Pa−1 were measured in the temperature range of 303–460 K. Comparison of Eact, selectivity and He and N2 permeation of different samples evidenced the dependence of nitrogen flux on processing defects. Obviously permeation rate of nitrogen molecule was insignificant through majority pores of the membrane

Inactivation of Vibrio vulnificus hemolysin through mutation of the N- or C-terminus of the lectin-like domain

Vibrio vulnificus is an etiological agent causing serious systemic infections in the immunocompromised humans or cultured eels. This species commonly produces a hemolytic toxin consisting of the cytolysin domain and the lectin-like domain. For hemolysis, the lectin-like domain specifically binds to cholesterol in the erythrocyte membrane, and to form a hollow oligomer, the toxin is subsequently assembled on the membrane. The cytolysin domain is essential for the process to form the oligomer. Three-dimensional structure model revealed that two domains connected linearly and the C-terminus was located near to the joint of the domains. Insertion of amino acid residues between two domains was found to cause inactivation of the toxin. In the C-terminus, deletion, substitution or addition of an amino acid residue also elicited reduction of the activity. However, the cholesterol-binding ability was not affected by the mutations. These results suggest that mutation of the C- or N-terminus of the lectin-like domain may result in blockage of the toxin assembly

Functional expression of the eukaryotic proton pump rhodopsin OmR2 in Escherichia coli and its photochemical characterization

Microbial rhodopsins are photoswitchable seven-transmembrane proteins that are widely distributed in three domains of life, archaea, bacteria and eukarya. Rhodopsins allow the transport of protons outwardly across the membrane and are indispensable for light-energy conversion in microorganisms. Archaeal and bacterial proton pump rhodopsins have been characterized using an Escherichia coli expression system because that enables the rapid production of large amounts of recombinant proteins, whereas no success has been reported for eukaryotic rhodopsins. Here, we report a phylogenetically distinct eukaryotic rhodopsin from the dinoflagellate Oxyrrhis marina (O. marina rhodopsin-2, OmR2) that can be expressed in E. coli cells. E. coli cells harboring the OmR2 gene showed an outward proton-pumping activity, indicating its functional expression. Spectroscopic characterization of the purified OmR2 protein revealed several features as follows: (1) an absorption maximum at 533 nm with all-trans retinal chromophore, (2) the possession of the deprotonated counterion (pK(a)=3.0) of the protonated Schiff base and (3) a rapid photocycle through several distinct photointermediates. Those features are similar to those of known eukaryotic proton pump rhodopsins. Our successful characterization of OmR2 expressed in E. coli cells could build a basis for understanding and utilizing eukaryotic rhodopsins

A blue-shifted anion channelrhodopsin from the Colpodellida alga Vitrella brassicaformis

Microbial rhodopsins, a family of photoreceptive membrane proteins containing the chromophore retinal, show a variety of light-dependent molecular functions. Channelrhodopsins work as light-gated ion channels and are widely utilized for optogenetics, which is a method for controlling neural activities by light. Since two cation channelrhodopsins were identified from the chlorophyte alga Chlamydomonas reinhardtii, recent advances in genomic research have revealed a wide variety of channelrhodopsins including anion channelrhodopsins (ACRs), describing their highly diversified molecular properties (e.g., spectral sensitivity, kinetics and ion selectivity). Here, we report two channelrhodopsin-like rhodopsins from the Colpodellida alga Vitrella brassicaformis, which are phylogenetically distinct from the known channelrhodopsins. Spectroscopic and electrophysiological analyses indicated that these rhodopsins are green- and blue-sensitive pigments (lambda(max) = similar to 550 and similar to 440 nm) that exhibit light-dependent ion channeling activities. Detailed electrophysiological analysis revealed that one of them works as a monovalent anion (Cl-, Br- and NO3-) channel and we named it V. brassicaformis anion channelrhodopsin-2, VbACR2. Importantly, the absorption maximum of VbACR2 (similar to 440 nm) is blue-shifted among the known ACRs. Thus, we identified the new blue-shifted ACR, which leads to the expansion of the molecular diversity of ACRs