Intracellular aggregation of the human amyloid protein α-synuclein is causally linked to Parkinson's disease. While the isolated protein is intrinsically disordered, its native structure in mammalian cells is not known. Here we use nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopy to derive atomic-resolution insights into the structure and dynamics of α-synuclein in different mammalian cell types. We show that the disordered nature of monomeric α-synuclein is stably preserved in non-neuronal and neuronal cells. Under physiological cell conditions, α-synuclein is amino-terminally acetylated and adopts conformations that are more compact than when in buffer, with residues of the aggregation-prone non-amyloid-β component (NAC) region shielded from exposure to the cytoplasm, which presumably counteracts spontaneous aggregation. These results establish that different types of crowded intracellular environments do not inherently promote α-synuclein oligomerization and, more generally, that intrinsic structural disorder is sustainable in mammalian cells.

Neurotransmission depends on presynaptic membrane retrieval and local reformation of synaptic vesicles (SVs) at nerve terminals. The mechanisms involved in these processes are highly controversial with evidence being presented for SV membranes being retrieved exclusively via clathrin-mediated endocytosis (CME) from the plasma membrane or via ultrafast endocytosis independent of clathrin. Here we show that clathrin and its major adaptor protein 2 (AP-2) in addition to the plasma membrane operate at internal endosome-like vacuoles to regenerate SVs but are not essential for membrane retrieval. Depletion of clathrin or conditional knockout of AP-2 result in defects in SV reformation and an accumulation of endosome-like vacuoles generated by clathrin-independent endocytosis (CIE) via dynamin 1/3 and endophilin. These results together with theoretical modeling provide a conceptual framework for how synapses capitalize on clathrin-independent membrane retrieval and clathrin/AP-2-mediated SV reformation from endosome-like vacuoles to maintain excitability over a broad range of stimulation frequencies.

The b-adrenergic receptor/cyclic AMP/protein kinase A (PKA) signalling pathway regulates heart rate and contractility. Here, we identified a supramolecular complex consisting of the sarcoplasmic reticulum Ca 2 þ -ATPase (SERCA2), its negative regulator phospholamban (PLN), the A-kinase anchoring protein AKAP18d and PKA. We show that AKAP18d acts as a scaffold that coordinates PKA phosphorylation of PLN and the adrenergic effect on Ca 2 þ re-uptake. Inhibition of the compartmentalization of this cAMP signalling complex by specific molecular disruptors interferes with the phosphorylation of PLN. This prevents the subsequent release of PLN from SERCA2, thereby affecting the Ca 2 þ re-uptake into the sarcoplasmic reticulum induced by adrenergic stimuli.

Vasopressin regulates water reabsorption in renal collecting duct principal cells by a cAMP-dependent translocation of the water channel aquaporin-2 (AQP2) from intracellular vesicles into the cell membrane. In the present work primary cultured inner medullary collecting duct cells were used to study the role of the proteins of the Rho family in the translocation of AQP2. Clostridium difficile toxin B, which inhibits all members of the Rho family, Clostridium limosum C3 toxin, which inactivates only Rho, and the Rho kinase inhibitor, Y-27632, induced both depolymerization of actin stress fibers and AQP2 translocation in the absence of vasopressin. The data suggest an inhibitory role of Rho in this process, whereby constitutive membrane localization is prevented in resting cells. Expression of constitutively active RhoA induced formation of actin stress fibers and abolished AQP2 translocation in response to elevation of intracellular cAMP, confirming the inhibitory role of Rho. Cytochalasin D induced both depolymerization of the F-actin cytoskeleton and AQP2 translocation, indicating that depolymerization of F-actin is sufficient to induce AQP2 translocation. Thus Rho is likely to control the intracellular localization of AQP2 via regulation of the F-actin cytoskeleton.The antidiuretic hormone arginine-vasopressin (AVP) 1 regulates water reabsorption in renal collecting duct principal cells by inducing the translocation of the water channel aquaporin-2 (AQP2) from intracellular vesicles primarily into the apical cell membrane (shuttle hypothesis; Refs. 1 and 2). The molecular targets of AVP on the surface of principal cells are heptahelical vasopressin V2 receptors coupled to the G s /adenylyl cyclase system. Activation of this system by the hormone raises the level of intracellular cAMP and results in the activation of protein kinase A (PKA) which then phosphorylates its substrates, one of which is AQP2.The phosphorylation of AQP2 by PKA and also the anchoring of PKA to subcellular compartments via protein kinase A anchoring proteins are prerequisites for AQP2 translocation to the cell membrane (2-5). In addition, the involvement of a heterotrimeric G protein of the G i family in the AQP2 translocation has been demonstrated in CD8 cells (6).The cytoskeleton consists of various components, including microtubules and F-actin, both of which are involved in AVPmediated changes of osmotic water permeability (2, 7-9). Microtubule-disrupting drugs like colchicine and nocodazole inhibit AVP-mediated increases in osmotic water permeability in renal collecting ducts by 65 and 72%, respectively (10 -13). Disruption of the F-actin cytoskeleton by cytochalasin B or dihydrocytochalasin B inhibits the AVP-induced increase in osmotic water permeability in toad bladder epithelium by 25-50% (13, 14). The F-actin cytoskeleton also undergoes rearrangements after stimulation of cells with cAMP-elevating agents. After stimulation with vasopressin, total F-actin decreases in toad bladders by 20 -30% (15) and apical F-actin in rat coll...

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A ntidiuretic hormone (arginine vasopressin [AVP]) induces fusion of vesicles that contain the water channel aquaporin-2 (AQP2) with the plasma membrane of renal collecting duct principal cells. This "AQP2 shuttle" increases the osmotic water permeability (Pf) of the cells, facilitating water reabsorption from the collecting duct (1). The AQP2 shuttle is initiated upon binding of AVP to vasopressin-2 receptors (V2R) and triggered by the consequent cAMP elevation and protein kinase A (PKA) activation. It is the PKA phosphorylation of AQP2 that elicits redistribution of AQP2-bearing vesicles. Pivotal to this redistribution is the compartmentalization of PKA by A kinase anchoring proteins (AKAP) (2). Phosphodiesterases (PDE), which are the sole means of degrading cAMP, are poised to regulate PKA signaling (3-6). The PDE4 family has attracted great interest because of its link to stroke (7), schizophrenia (8), and the therapeutic potential of selective inhibitors for treating inflammatory diseases (9-12). The four subfamilies (PDE4A through D) are encoded by separate genes, generating approximately 20 isoforms (9,11) that can interact with scaffolding proteins, including AKAP and ␤-arrestin (12-16), positioning them for a role in compartmentalized cAMP/PKA signaling.Here we show that compartmentalization of cAMP/PKA signaling by PDE4 is involved in the regulation of the AQP2 shuttle and the Pf. This is of particular pertinence because PDE4 hyperactivity causes nephrogenic diabetes insipidus in a mouse model (17).

A-kinase anchoring proteins (AKAPs) tether protein kinase A (PKA) and other signaling proteins to defined intracellular sites, thereby establishing compartmentalized cAMP signaling. AKAP-PKA interactions play key roles in various cellular processes, including the regulation of cardiac myocyte contractility. We discovered small molecules, 3,3′-diamino-4,4′-dihydroxydiphenylmethane (FMP-API-1) and its derivatives, which inhibit AKAP-PKA interactions in vitro and in cultured cardiac myocytes. The molecules bind to an allosteric site of regulatory subunits of PKA identifying a hitherto unrecognized region that controls AKAP-PKA interactions. FMP-API-1 also activates PKA. The net effect of FMP-API-1 is a selective interference with compartmentalized cAMP signaling. In cardiac myocytes, FMP-API-1 reveals a novel mechanism involved in terminating β-adrenoreceptor-induced cAMP synthesis. In addition, FMP-API-1 leads to an increase in contractility of cultured rat cardiac myocytes and intact hearts. Thus, FMP-API-1 represents not only a novel means to study compartmentalized cAMP/PKA signaling but, due to its effects on cardiac myocytes and intact hearts, provides the basis for a new concept in the treatment of chronic heart failure.

Biologically inert, photoactivatable precursors ("caged" compounds) of cyclic nucleoside monophosphates (cNMPs) are powerful tools for studying the spatiotemporal dynamics of cyclic nucleotide dependent processes. Among these compounds, (coumarin-4-yl)methyl esters of cNMPs are most useful because they show no background bioactivity, are stable to solvolysis, and can be photolyzed efficiently and extremely quickly. [1,2] Recently, we introduced [7-(diethylamino)coumarin-4-yl]methyl (DEACM) esters of cNMPs as caged compounds. [3,4] Compared with other coumarinylmethyl-caged cNMPs, the DEACM esters photorelease cNMPs with higher photosensitivity at long-wavelength irradiation (up to 436 nm), thus minimizing or even preventing damage to cellular components and chromophores by photobleaching.Herein, we describe the development of the 7-[bis(carboxymethyl)amino]-substituted coumarinylmethyl building blocks 1 and 2 (structures in Scheme 1) for the caging of phosphates and other functionalities. With the axial and the equatorial diastereomers of the {7-[bis(carboxymethyl)-amino]coumarin-4-yl}methyl (BCMACM) esters of cAMP, cGMP, 8-Br-cAMP, and 8-Br-cGMP 3-6 (Scheme 1), we present new variants of the DEACM-caged cNMPs, which maintain their favorable properties and additionally have much higher aqueous solubility by virtue of their anionic[*] Dr.