Highly efficient energy transfer from a water soluble quantum dot to organic J-aggregates in an inorganic–organic nanohybrid associate.

Phosphoprotein (P) of negative sense RNA viruses functions as a transcriptional transactivator of the viral polymerase (L). We report here the characterization of oligomeric P protein of rinderpest virus (RPV) and provide a structural basis for its multimerization. By size exclusion chromatography and dynamic light scattering analyses we show that bacterially expressed P protein exists as an oligomer, thus excluding the role of phosphorylation in P protein oligomerization. Gel filtration analyses of various parts of the P protein, also expressed in Escherichia coli, revealed that the predicted coiled coil region in the C-terminal domain is responsible for P protein oligomerization. Dynamic light scattering analysis confirmed the oligomeric nature of the coiled coil region of P. Chemical cross-linking analysis suggested that the C-terminal coiled coil region exists as a tetramer. The tetramer is formed by coiled coil interaction as shown by circular dichroism spectral analysis. Based on sequence homology, we propose a three-dimensional structure of the multimerization domain of RPV P using the crystal structure for multimerization domain of sendai virus (SeV) P as a template. Four-stranded coiled coil structure of the model is stabilized by a series of interactions predominantly between short nonpolar side chains emerging from different strands. In an in vivo replication/transcription system using a synthetic minigenome of RPV, we show that multimerization is essential for P protein function(s), and the multimerization domain is highly conserved between two morbilliviruses namely RPV and peste de petits ruminants virus. These results are discussed in the context of biological functions of P protein among various negative-stranded RNA viruses.

Dense core granules (DCGs) in Tetrahymena thermophila contain two protein classes. Proteins in the first class, called granule lattice (Grl), coassemble to form a crystalline lattice within the granule lumen. Lattice expansion acts as a propulsive mechanism during DCG release, and Grl proteins are essential for efficient exocytosis. The second protein class, defined by a C-terminal ␤/␥-crystallin domain, is poorly understood. Here, we have analyzed the function and sorting of Grt1p (granule tip), which was previously identified as an abundant protein in this family. Cells lacking all copies of GRT1, together with the closely related GRT2, accumulate wild-type levels of docked DCGs. Unlike cells disrupted in any of the major GRL genes, ⌬GRT1 ⌬GRT2 cells show no defect in secretion, indicating that neither exocytic fusion nor core expansion depends on GRT1. These results suggest that Grl protein sorting to DCGs is independent of Grt proteins. Consistent with this, the granule core lattice in ⌬GRT1 ⌬GRT2 cells appears identical to that in wild-type cells by electron microscopy, and the only biochemical component visibly absent is Grt1p itself. Moreover, gel filtration showed that Grl and Grt proteins in cell homogenates exist in nonoverlapping complexes, and affinity-isolated Grt1p complexes do not contain Grl proteins. These data demonstrate that two major classes of proteins in Tetrahymena DCGs are likely to be independently transported during DCG biosynthesis and play distinct roles in granule function. The role of Grt1p may primarily be postexocytic; consistent with this idea, DCG contents from ⌬GRT1 ⌬GRT2 cells appear less adhesive than those from the wild type.

A mesoporous silica-based inorganic-organic hybrid material (NBD-AP-MCM) has been designed and developed as a fluorescent chemosensor for the detection of fluoride in aqueous medium. The system was developed by covalently anchoring 7-nitro-2,1,3-benzoxadiazole (NBD) dye onto the surface of mesoporous silica nanoparticles, MCM-41. The system was characterized using several conventional analytical methods comprising spectroscopic, microscopic and thermo-gravimetric techniques. The sensory action of the material was investigated by carrying out steady state absorbance, fluorescence and time resolved fluorescence studies on the system in the absence and presence of several biologically and environmentally important anions in aqueous solution. The photophysical data of the present system (NBD-AP-MCM) have also been compared with the free dye (NBD) molecules. A significant decrease in the fluorescence quantum yield of the fluorophore in the hybrid material NBD-AP-MCM has been observed as compared to the unbound NBD. The decrease in fluorescence efficiency in the hybrid material is attributed to the aggregation caused quenching (ACQ) phenomenon. Interestingly, the system displays more than six-fold fluorescence enhancement in the presence of fluoride ions in aqueous solution. Enhancement of the fluorescence lifetime of the fluorescing moiety (NBD) has also been observed during fluorescence time-resolved studies. No significant optical changes have been observed with other commonly encountered anions rendering the present system highly selective towards fluoride detection. The fluorescence enhancement has been attributed to the cleavage of Si-O bonds due to the addition of fluoride. The silyl cleavage detaches the fluorophore from the solid support thereby making the fluorophore "free" in solution, which in turn recovers its original fluorescence which was decreased because of the aggregation on the solid silica support. Furthermore, the suitability of the present system in cellular imaging has also been demonstrated.

A series of 4-bromonaphthalimide systems (BNI-C n ; n = 4, 6, 10, 12, and 16) comprising different alkyl side chains have been synthesized and used as the building blocks to fabricate organic fluorescent micro materials. The systems have been developed basically to investigate the effect of alkyl side chains on the aggregation behavior of the systems. The aggregation behavior of these systems has been studied by spectroscopic and microscopic techniques. Microscopic investigation reveals that there is a decrease in the size of the aggregates with an increase in the linear alkyl side chain length. A change in the shape from rod-like to spherical with an increase in the length of alkyl group has also been observed during microscopic investigation. The photophysical properties of these well-characterized aggregates have been studied and compared with those in molecular form. A bathochromic shift both in absorption and in emission spectrum of the aggregates has indicated the formation of J aggregates. A confocal fluorescence microscopic investigation also reveals that the long chain systems (12 and 16 member) are cell permeable and can be used as the imaging probe in live cells.