P2X receptor trafficking in neurons is subunit specific

P2X receptors within the CNS mediate excitatory synaptic transmission and also act presynaptically to modulate neurotransmitter release. We have studied the targeting and trafficking of P2X4 and P2X2 receptors heterologously expressed in cultured olfactory bulb neurons. Homomeric P2X4 receptors had a punctate distribution, and many of the puncta colocalized with early endosomes. In contrast, P2X2 receptors were primarily localized at the plasma membrane. By antibody-labeling of surface receptors in living neurons, we showed that P2X4 receptors undergo rapid constitutive internalization and subsequent reinsertion into the plasma membrane, whereas P2X2 receptors were not regulated in such a way. The internalization of P2X4 receptors was dynamin-dependent, and the binding of ATP enhanced the basal rate of retrieval in a Ca2+-independent manner. The presence of the P2X4 subunit in a P2X4/6 heteromer governed the trafficking properties of the receptor. P2X receptors acted presynaptically to enhance the release of glutamate, suggesting that the regulated cycling of P2X4-containing receptors might provide a mechanism for modulation of synaptic transmission

Crystal Structures of Polymerized Fullerides AC60, A=K, Rb, Cs and Alkali-mediated Interactions

Starting from a model of rigid interacting C60 polymer chains on an orthorhombic lattice, we study the mutual orientation of the chains and the stability of the crystalline structures Pmnn and I2/m. We take into account i) van der Waals interactions and electric quadrupole interactions between C60 monomers on different chains as well as ii) interactions of the monomers with the surrounding alkali atoms. The direct interactions i) always lead to an antiferrorotational structure Pmnn with alternate orientation of the C60 chains in planes (001). The interactions ii) with the alkalis consist of two parts: translation-rotation (TR) coupling where the orientations of the chains interact with displacements of the alkalis, and quadrupolar electronic polarizability (ep) coupling, where the electric quadrupoles on the C60 monomers interact with induced quadrupoles due to excited electronic d states of the alkalis. Both interactions ii) lead to an effective orientation-orientation interaction between the C60 chains and always favor the ferrorotational structure I2/m where C60 chains have a same orientation. The structures Pmnn for KC60 and I2/m for Rb- and CsC60 are the result of a competition between the direct interaction i) and the alkali-mediated interactions ii). In Rb- and CsC60 the latter are found to be dominant, the preponderant role being played by the quadrupolar electronic polarizability of the alkali ions.Comment: J.Chem.Phys., in press, 14 pages, 3 figures, 8 table

Draft Genome Sequences of Facultative Methylotrophs, Gemmobacter sp. Strain LW1 and Mesorhizobium sp. Strain 1M-11, Isolated from Movile Cave, Romania

Facultative methylotrophs belonging to the genera Gemmobacter and Mesorhizobium were isolated from microbial mat and cave water samples obtained from the Movile Cave ecosystem. Both bacteria can utilize methylated amines as their sole carbon and nitrogen source. Here, we report the draft genome sequences of Gemmobacter sp. strain LW1 and Mesorhizobium sp. strain IM1

Substrate-specific clades of active marine methylotrophs associated with a phytoplankton bloom in a temperate coastal environment

Marine microorganisms that consume one-carbon (C1) compounds are poorly described, despite their impact on global climate via an influence on aquatic and atmospheric chemistry. This study investigated marine bacterial communities involved in the metabolism of C1 compounds. These communities were of relevance to surface seawater and atmospheric chemistry in the context of a bloom that was dominated by phytoplankton known to produce dimethylsulfoniopropionate. In addition to using 16S rRNA gene fingerprinting and clone libraries to characterize samples taken from a bloom transect in July 2006, seawater samples from the phytoplankton bloom were incubated with 13C-labeled methanol, monomethylamine, dimethylamine, methyl bromide, and dimethyl sulfide to identify microbial populations involved in the turnover of C1 compounds, using DNA stable isotope probing. The [13C]DNA samples from a single time point were characterized and compared using denaturing gradient gel electrophoresis (DGGE), fingerprint cluster analysis, and 16S rRNA gene clone library analysis. Bacterial community DGGE fingerprints from 13C-labeled DNA were distinct from those obtained with the DNA of the nonlabeled community DNA and suggested some overlap in substrate utilization between active methylotroph populations growing on different C1 substrates. Active methylotrophs were affiliated with Methylophaga spp. and several clades of undescribed Gammaproteobacteria that utilized methanol, methylamines (both monomethylamine and dimethylamine), and dimethyl sulfide. rRNA gene sequences corresponding to populations assimilating 13C-labeled methyl bromide and other substrates were associated with members of the Alphaproteobacteria (e.g., the family Rhodobacteraceae), the Cytophaga-Flexibacter-Bacteroides group, and unknown taxa. This study expands the known diversity of marine methylotrophs in surface seawater and provides a comprehensive data set for focused cultivation and metagenomic analyses in the future

The stoichiometry of P2X2/6 receptor heteromers depends on relative subunit expression levels

Fast synaptic transmission involves the operation of ionotropic receptors, which are often composed of at least two types of subunit. We have developed a method, based on atomic force microscopy imaging to determine the stoichiometry and subunit arrangement within ionotropic receptors. We showed recently that the P2X(2) receptor for ATP is expressed as a trimer but that the P2X(6) subunit is unable to oligomerize. In this study we addressed the subunit stoichiometry of heteromers containing both P2X(2) and P2X(6) subunits. We transfected tsA 201 cells with both P2X(2) and P2X(6) subunits, bearing different epitope tags. We manipulated the transfection conditions so that either P2X(2) or P2X(6) was the predominant subunit expressed. By atomic force microscopy imaging of isolated receptors decorated with antiepitope antibodies, we demonstrate that when expression of the P2X(2) subunit predominates, the receptors contain primarily 2 x P2X(2) subunits and 1 x P2X(6) subunit. In contrast, when the P2X(6) subunit predominates, the subunit stoichiometry of the receptors is reversed. Our results show that the composition of P2X receptor heteromers is plastic and dependent on the relative subunit expression levels. We suggest that this property of receptor assembly might introduce an additional layer of subtlety into P2X receptor signaling

Comparison of bacterioneuston and bacterioplankton dynamics during a phytoplankton bloom in a fjord mesocosm

The bacterioneuston is the community of Bacteria present in surface microlayers, the thin surface film that forms the interface between aquatic environments and the atmosphere. In this study we compared bacterial cell abundance and bacterial community structure of the bacterioneuston and the bacterioplankton (from the subsurface water column) during a phytoplankton bloom mesocosm experiment. Bacterial cell abundance, determined by flow cytometry, followed a typical bacterioplankton response to a phytoplankton bloom, with Synechococcus and high nucleic acid (HNA) bacterial cell numbers initially falling, probably due to selective protist grazing. Subsequently HNA and low nucleic acid (LNA) bacterial cells increased in abundance but Synechococcus did not. There was no significant difference between bacterioneuston and bacterioplankton cell abundances during the experiment. Conversely, distinct and consistent differences between the bacterioneuston and the bacterioplankton community structure were observed. This was monitored simultaneously by Bacteria 16S rRNA gene terminal restriction fragment length polymorphism (T-RFLP) and denaturing gradient gel electrophoresis (DGGE). The conserved patterns of community structure observed in all of the mesocosms indicate that the bacterioneuston is distinctive and non-random