Bacterial chemoreceptors are transmembrane homodimers that can form trimers, higher order arrays, and extended clusters as part of signaling complexes. Interactions of dimers in oligomers are thought to confer cooperativity and cross-receptor influences as well as a 35-fold gain between ligand binding and altered kinase activity. In addition, higher order interactions among dimers are necessary for the observed patterns of assistance in adaptational modification among different receptors. Elucidating mechanisms underlying these properties will require defining which receptor functions can be performed by dimers and which require specific higher order interactions. However, such an assignment has not been possible. Here, we used Nanodiscs, an emerging technology for manipulating membrane proteins, to prepare small particles of lipid bilayer containing one or only a few chemoreceptor dimers. We found that receptor dimers isolated in individual Nanodiscs were readily modified, bound ligand, and performed transmembrane signaling. However, they were hardly able to activate the chemotaxis histidine kinase. Instead, maximal activation and thus full-range control of kinase occurred preferentially in discs containing approximately three chemoreceptor dimers. The sharp dependence of kinase activation on this number of receptors per dimer implies that the core structural unit of kinase activation and control is a trimer of dimers. Thus, our observations demonstrate that chemoreceptor transmembrane signaling does not require oligomeric organization beyond homodimers and implicate a trimer of dimers as the unit of downstream signaling. membrane protein ͉ nanoparticle ͉ self-assembly ͉ transmembrane receptor ͉ transmembrane signaling M otile bacteria move to favorable chemical environments through chemotaxis. The phenomenon and its mechanisms have been extensively characterized in Escherichia coli and its relatives (1-3). Transmembrane chemoreceptors form signaling complexes with the autophosphorylating histidine kinase CheA and coupling protein CheW. Phospho-CheA mediates phosphorylation of response regulator CheY. Phospho-CheY binds to the flagellar rotary motor, causing rotational reversal, which creates tumbles that alter swimming direction. Formation of signaling complexes activates CheA autophosphorylation and places that activity under the control of chemoreceptors. The sensory system directs cells toward favorable environments by modulating kinase activity, thus controlling the probability of tumbles and resulting directional changes. Transmembrane SignalingTransmembrane signaling by chemoreceptors (3) couples binding of stimulant molecules by its periplasmic domain with changes in its cytoplasmic domain that alter activation of the kinase and change the propensity for covalent modification of that domain, specifically methylation and demethylation at several glutamyl residues (four to six, depending on the specific receptor). Methylation is catalyzed by methyltransferase CheR. Demethylation is catalyzed by methyleste...

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An ultrafast thulium-doped fiber laser with large net normal dispersion has been developed to produce dissipative soliton and noise-like outputs at 1.9 μm. The mode-locked operation was enabled by using single-wall carbon nanotubes as saturable absorber for all-fiber configuration. Dissipative soliton in normal dispersion produced by the fiber laser oscillator was centered at 1947 nm with 4.1-nm FWHM bandwidth and 0.45 nJ/pulse. The output dissipative soliton pulses were compressed to 2.3 ps outside the laser cavity.

Cells primarily rely on proteins to perform the majority of their physiological functions, and the function of proteins is regulated by post-translational modifications (PTMs). The acetylation of proteins is a dynamic and highly specific PTM, which has an important influence on the functions of proteins, such as gene transcription and signal transduction. The acetylation of proteins is primarily dependent on lysine acetyltransferases and lysine deacetylases. In recent years, due to the widespread use of mass spectrometry and the emergence of new technologies, such as protein chips, studies on protein acetylation have been further developed. Compared with histone acetylation, acetylation of non-histone proteins has gradually become the focus of research due to its important regulatory mechanisms and wide range of applications. The discovery of specific protein acetylation sites using bioinformatic tools can greatly aid the understanding of the underlying mechanisms of protein acetylation involved in related physiological and pathological processes. Contents 1. Introduction 2. Discovery and concepts of protein acetylation and deacetylation 3. Diseases and protein acetylation and deacetylation 4. Protein acetylation and deacetylation in stem cells 5. Tools to predict acetylation sites 6. Conclusions and prospects

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