Photoactive ligands probing the sweet taste receptor. Design and synthesis of highly potent diazirinyl d-phenylalanine derivatives

Some d-Amino acids such as d-tryptophan and d-phenylalanine are well known as naturally-occurring sweeteners. Photoreactive d-phenylalanine derivatives containing trifluoromethyldiazirinyl moiety at 3- or 4-position of phenylalanine, were designed as sweeteners for functional analysis with photoaffinity labeling. The trifluoromethyldiazirinyl d-phenylalanine derivatives were prepared effectively with chemo-enzymatic methods using l-amino acid oxidase and were found to have potent activity toward the human sweet taste receptor.     

Mff is an essential factor for mitochondrial recruitment of Drp1 during mitochondrial fission in mammalian cells

The cytoplasmic dynamin-related guanosine triphosphatase Drp1 is recruited to mitochondria and mediates mitochondrial fission. Although the mitochondrial outer membrane (MOM) protein Fis1 is thought to be a Drp1 receptor, this has not been confirmed. To analyze the mechanism of Drp1 recruitment, we manipulated the expression of mitochondrial fission and fusion proteins and demonstrated that (a) mitochondrial fission factor (Mff) knockdown released the Drp1 foci from the MOM accompanied by network extension, whereas Mff overexpression stimulated mitochondrial recruitment of Drp1 accompanied by mitochondrial fission; (b) Mff-dependent mitochondrial fission proceeded independent of Fis1; (c) a Mff mutant with the plasma membrane-targeted CAAX motif directed Drp1 to the target membrane; (d) Mff and Drp1 physically interacted in vitro and in vivo; (e) exogenous stimuli-induced mitochondrial fission and apoptosis were compromised by knockdown of Drp1 and Mff but not Fis1; and (f) conditional knockout of Fis1 in colon carcinoma cells revealed that it is dispensable for mitochondrial fission. Thus, Mff functions as an essential factor in mitochondrial recruitment of Drp1.     

Dynamics of Golgi matrix proteins after the blockage of ER to Golgi transport

When the ER to Golgi transport is blocked by a GTP-restricted mutant of Sar1p (H79G) in NRK-52E cells, most Golgi resident proteins are transported back into the ER. In contrast, the cis-Golgi matrix proteins GM130 and GRASP65 are retained in punctate cytoplasmic structures, namely Golgi remnants. Significant amounts of the medial-Golgi matrix proteins golgin-45, GRASP55 and giantin are retained in the Golgi remnants, but a fraction of these proteins relocates to the ER. Golgin-97, a candidate trans-Golgi network matrix protein, is retained in Golgi remnant-like structures, but mostly separated from GM130 and GRASP65. Interestingly, most Sec13p, a COPII component, congregates into larger cytoplasmic clusters soon after the microinjection of Sar1p(H79G), and these move to accumulate around the Golgi apparatus. Sec13p clusters remain associated with Golgi remnants after prolonged incubation. Electron microscopic analysis revealed that Golgi remnants are clusters of larger vesicles with smaller vesicles, many of which are coated. GM130 is mainly associated with larger vesicles and Sec13p with smaller coated vesicles. The Sec13p clusters disperse when p115 binding to the Golgi apparatus is inhibited. These results suggest that cis-Golgi matrix proteins resist retrograde transport flow and stay as true residents in Golgi remnants after the inhibition of ER to Golgi transport.     

Gelation behaviors of schizophyllan-sorbitol aqueous solutions

On addition of D-sorbitol, schizophyllan (SPG) aqueous solution forms a thermoreversible gel upon cooling. The gelation process is characterized by rheology, differential scanning calorimetry (DSC), and optical rotation measurement (ORD). It is found that the Winter-Chambon criterion works well in determining the critical gelation point of the present system, although the criterion has been scarcely applicable to systems that show weak-gel properties even before gelation. Moreover, ORD and DSC results indicate that a disordered to ordered conformational change accompanies the gelation process, which is attributed to the transition from SPG triple helix II to I. The gelation temperature of SPG-sorbitol aqueous solution is almost independent of SPG concentration in the examined concentration range and is slightly decreased by lowering SPG molecular weight, while greatly influenced by sorbitol content. The gelation is considered to be induced by the transition from SPG triple helix II to I, which leads to a three-dimensional network constituted by the extremely entangled and stiff SPG triple helices I. Furthermore, it is proved that neither junction zone nor aggregation of SPG triple helices is involved in the SPG-sorbitol gels. The SPG-sorbitol gel is structurally like a solution that is unable to flow within a timescale of usual observation.     

Rheological characterization of schizophyllan aqueous solutions after denaturation-renaturation treatment

Schizophyllan (SPG) with a molecular weight of 2.6x10(6), designated SPG-1, is denatured and then renatured at a concentration of 1.8 wt % by alkalization-neutralization. The prepared denatured-renatured samples (DRSPG-1) are diluted to various concentrations and equilibrated for 10 days before rheological and intrinsic viscosity measurements. When concentration (C(p)) is above 0.75 wt %, DRSPG-1 aqueous systems have weak gel-type rheological properties. However, for 0.28 wt % 相似文献   

Selective detection of L-glutamate using a microfluidic device integrated with an enzyme-modified pre-reactor and an electrochemical detector

A microfluidic device integrated with a nanoliter volume enzyme pre-reactor and an enzyme-modified electrode was developed for the highly selective continuous measurement of glutamate (Glu). The device consists mainly of two glass plates. One plate incorporates an electrochemical cell that consists of working electrode (WE), reference electrode (RE) and counter electrode (CE). The WE is modified with a bilayer film of Os-polyvinylpyrridine-based mediator containing horseradish peroxidase (Os-gel-HRP). The WE was operated at -50 mV versus Ag. The other plate has a thin layer flow channel integrated with a pre-reactor. The reactor has a number of micropillars (20 microm in diameter, 20 microm high and separated from each other by a 20 microm gap) modified with ascorbate oxidase (AAOx) to eliminate L-ascorbic acid (AA). The enzymatic oxidation of AA is superior to that obtained with our previously reported pre-electrolysis type micro-reactor since electrochemically reversible transmitters such as catecholamines do not provide a cathodic current at the WE. In addition, the high operation potential of the pre-reactor causes unknown electroactive species, which also cause interference at the detection electrode. As a result, we were able to detect 1 microM Glu continuously at a low flow rate even when AA concentration was 100 microM.     

Identification and characterization of the pswP gene required for the parallel production of prodigiosin and serrawettin W1 in Serratia marcescens

Serratia marcescens mutants defective in production of the red pigment prodigiosin and the biosurfactant serrawettin W1 in parallel were isolated by transposon mutagenesis of strain 274. Cloning of the DNA fragment required for production of these secondary metabolites with different chemical structures pointed out a novel open reading frame (ORF) named pswP. The putative product PswP (230 aa) has the distinct signature sequence consensus among members of phosphopantetheinyl transferase (PPTase) which phosphopantetheinylates peptidyl carrier protein (PCP) mostly integrated in the nonribosomal peptide synthetases (NRPSs) system. Since serrawettin W1 belongs to the cyclodepsipeptides, which are biosynthesized through the NRPSs system, and one pyrrole ring in prodigiosin has been reported as a derivative of L -proline tethered to phosphopantetheinylated PCP, the mutation in the single gene pswP seems responsible for parallel failure in production of prodigiosin and serrawettin W1.     

Sequence-specific cleavage of small-subunit (SSU) rRNA with oligonucleotides and RNase H: a rapid and simple approach to SSU rRNA-based quantitative detection of microorganisms

A rapid and simple approach to the small-subunit (SSU) rRNA-based quantitative detection of a specific group of microorganisms in complex ecosystems has been developed. The method employs sequence-specific cleavage of rRNA molecules with oligonucleotides and RNase H. Defined mixtures of SSU rRNAs were mixed with an oligonucleotide (referred to as a "scissor probe") that was specifically designed to hybridize with a particular site of targeted rRNA and were subsequently digested with RNase H to proceed to sequence-dependent rRNA scission at the hybridization site. Under appropriate reaction conditions, the targeted rRNAs were correctly cut into two fragments, whereas nontargeted rRNAs remained intact under the same conditions. The specificity of the cleavage could be properly adjusted by controlling the hybridization stringency between the rRNA and the oligonucleotides, i.e., by controlling either the temperature of the reaction or the formamide concentration in the hybridization-digestion buffer used for the reaction. This enabled the reliable discrimination of completely matched rRNA sequences from single-base mismatched sequences. For the detection of targeted rRNAs, the resulting RNA fragment patterns were analyzed by gel electrophoresis with nucleotide-staining fluorescent dyes in order to separate cleaved and intact rRNA molecules. The relative abundance of the targeted SSU rRNA fragments in the total SSU rRNA could easily be calculated without the use of an external standard by determining the signal intensity of individual SSU rRNA bands in the electropherogram. This approach provides a fast and easy means of identification, detection, and quantification of a particular group of microbes in clinical and environmental specimens based on rRNA.     

Targeting and assembly of mitochondrial tail-anchored protein Tom5 to the TOM complex depend on a signal distinct from that of tail-anchored proteins dispersed in the membrane

Mitochondrial outer membrane proteins are synthesized without a cleavable presequence but instead contain segments responsible for mitochondrial targeting and membrane integration within the molecule: the transmembrane segment (TMS) and N- or C-terminal flanking segment. We analyzed targeting and integration of Tom5, a C-tail anchor protein associated with the preprotein translocase of the outer membrane, to the yeast mitochondrial outer membrane in vivo using green fluorescent protein as the reporter and compared the signal with other signals for proteins dispersed in the membrane. The functional assembly of Tom5 into the TOM complex was assessed by blue native PAGE and complementation of temperature-sensitive deltatom5 cells. Correct targeting and assembly required (i). an appropriate length TMS rather than hydrophobicity, (ii). a proline residue located at correct position in the TMS and specific residues near the proline, and (iii). that, in contrast to proteins dispersed in the outer membrane, the positive C-terminal segment was dispensable. Based on these findings, we constructed green fluorescent protein fusions with a C-terminal TMS in which the deduced sequences (minimum: Ser-Pro-Met) were inserted at an appropriate position within artificial Leu-Ala repeats. They were targeted to mitochondria and complemented the temperature-sensitive growth phenotype of deltatom5 yeast cells. The membrane-targeting mechanism of Tom5 appears to be distinct from that for proteins that are dispersed in the outer membrane.