The potassium chloride cotransporter KCC2 plays a major role in the maintenance of transmembrane chloride potential in mature neurons; thus KCC2 activity is critical for hyperpolarizing membrane currents generated upon the activation of ␥-aminobutyric acid type A and glycine (Gly) receptors that underlie fast synaptic inhibition in the adult central nervous system. However, to date an understanding of the cellular mechanism that neurons use to modulate the functional expression of KCC2 remains rudimentary. Using Escherichia coli expression coupled with in vitro kinase assays, we first established that protein kinase C (PKC) can directly phosphorylate serine 940 (Ser 940) within the C-terminal cytoplasmic domain of KCC2. We further demonstrated that Ser 940 is the major site for PKC-dependent phosphorylation for full-length KCC2 molecules when expressed in HEK-293 cells. Phosphorylation of Ser 940 increased the cell surface stability of KCC2 in this system by decreasing its rate of internalization from the plasma membrane. Coincident phosphorylation of Ser 940 increased the rate of ion transport by KCC2. It was further evident that phosphorylation of endogenous KCC2 in cultured hippocampal neurons is regulated by PKC-dependent activity. Moreover, in keeping with our recombinant studies, enhancing PKC-dependent phosphorylation increased the targeting of KCC2 to the neuronal cell surface. Our studies thus suggest that PKC-dependent phosphorylation of KCC2 may play a central role in modulating both the functional expression of this critical transporter in the brain and the strength of synaptic inhibition. Cation-chloride cotransporters (CCC)3 regulate Cl Ϫ homeostasis in cells and the generation of transmembrane chloride gradients (1). Adult mammalian neurons maintain low intracellular Cl Ϫ concentrations, which arise principally from the activity of the potassium chloride cotransporter-2 (KCC2). The maintenance of such low levels of intracellular Cl Ϫ ions is responsible for hyperpolarizing Cl Ϫ currents upon activation of GABA A and Gly receptors, which are responsible for fast synaptic inhibition in the adult central nervous system (2-5). Molecular studies have demonstrated that KCC2 is a member of a CCC superfamily and that these transporters are composed of 12-transmembrane domains with N-and C-terminal cytoplasmic domains (2, 6, 7). KCC2 is expressed exclusively in neurons throughout the adult brain. Developmentally KCC2 is first detected around 10 days in vitro in cultured rat neurons, which is coincident with the emergence of hyperpolarizing GABA A receptor-mediated Cl Ϫ currents (4, 8). Gene knock-out of KCC2 has revealed that ablating the expression of this protein results in early postnatal death. Neurons derived from these animals exhibit compromised GABA A receptor-mediated synaptic inhibition (9).Under pathological conditions such as epilepsy or ischemic brain injury, deficits in the expression of KCC2 are evident together with decreased efficacy of GABAergic inhibition and with the emergence of depola...

KCC2 is a neuron-specific K+-Cl− cotransporter that maintains a low intracellular Cl− concentration essential for hyperpolarizing inhibition mediated by GABAA receptors. Deficits in KCC2 activity occur in disease states associated with pathophysiological glutamate release. However, the mechanisms by which elevated glutamate levels alter KCC2 function are unknown. The phosphorylation of KCC2 residue S940 is known to regulate its surface activity. Here we demonstrated in dissociated rat neurons that NMDA receptor activity and Ca2+ influx caused the dephosphorylation of S940 leading to a loss of KCC2 function that lasted greater than 20 minutes. PP1 mediated the dephosphorylation events of S940 that coincided with a deficit in hyperpolarizing GABAergic inhibition due to the loss of KCC2 activity. Blocking dephosphorylation of S940 reduced the glutamate-induced downregulation of KCC2 and significantly improved the maintenance of hyperpolarizing GABAergic inhibition. Reducing the downregulation of KCC2 thus has therapeutic potential in the treatment of neurological disorders.

Fluorescent reporter proteins based on flavin-binding photosensors were recently developed as a new class of genetically encoded probes characterized by small size and oxygen-independent maturation of fluorescence. Flavin-based fluorescent proteins (FbFPs) address two major limitations associated with existing fluorescent reporters derived from the green fluorescent protein (GFP)–namely, the overall large size and oxygen-dependent maturation of fluorescence of GFP. However, FbFPs are at a nascent stage of development and have been utilized in only a handful of biological studies. Importantly, a full understanding of the performance and properties of FbFPs as a practical set of biological probes is lacking. In this work, we extensively characterize three FbFPs isolated from Pseudomonas putida, Bacillus subtilis, and Arabidopsis thaliana, using in vitro studies to assess probe brightness, oligomeric state, maturation time, fraction of fluorescent holoprotein, pH tolerance, redox sensitivity, and thermal stability. Furthermore, we validate FbFPs as stable molecular tags using in vivo studies by constructing a series of FbFP-based transcriptional constructs to probe promoter activity in Escherichia coli. Overall, FbFPs show key advantages as broad-spectrum biological reporters including robust pH tolerance (4–11), thermal stability (up to 60°C), and rapid maturation of fluorescence (<3 min.). In addition, the FbFP derived from Arabidopsis thaliana (iLOV) emerged as a stable and nonperturbative reporter of promoter activity in Escherichia coli. Our results demonstrate that FbFP-based reporters have the potential to address key limitations associated with the use of GFP, such as pH-sensitive fluorescence and slow kinetics of fluorescence maturation (10–40 minutes for half maximal fluorescence recovery). From this view, FbFPs represent a useful new addition to the fluorescent reporter protein palette, and our results constitute an important framework to enable researchers to implement and further engineer improved FbFP-based reporters with enhanced brightness and tighter flavin binding, which will maximize their potential benefits.

The nanoscience revolution that sprouted throughout the 1990s is having great impact in current and future DNA detection technology around the world. In this review, we report our recent progress on gold nanoparticle based fluorescence resonance energy transfer assay to monitor DNA hybridization as well as the cleavage of DNA by nucleases. We tried to discuss a reasonable account of the science and the important fundamental work carried out in this area. We also report the development of a compact, highly specific, inexpensive and user-friendly optical fiber laser-induced fluorescence sensor based on fluorescence quenching by nanoparticles to detect singlestrand DNA hybridization at femtomolar level.