The M 1 and M 3 subtypes are the major muscarinic acetylcholine receptors in the salivary gland and M 3 is reported to be more abundant. However, despite initial reports of salivation abnormalities in M 3 -knockout (M 3 KO) mice, it is still unclear which subtype is functionally relevant in physiological salivation. In the present study, salivary secretory function was examined using mice lacking specific subtype(s) of muscarinic receptor.

Store-operated calcium entry (SOCE) or I CRAC (calcium release-activated calcium current) is a critical pathway to replenish intracellular calcium stores, and plays indispensable roles in cellular functions such as antigen-induced T lymphocyte activation. Despite the importance of I CRAC in cellular functions, lack of potent and specific inhibitor has limited the approaches to the function of I CRAC in native cells. 2-Aminoethyl diphenylborinate (2-APB) is a widely used SOCE/I CRAC inhibitor, while its effect is rather unspecific. In the attempt to develop more potent and selective compounds here we identified two structurally isomeric 2-APB analogues that are 100-fold more potent than 2-APB itself. One of the 2-APB analogues activates and inhibits endogenous SOCE depending on the concentration while the other only inhibits it. The 2-APB analogue inhibits store depletion-mediated STIM1 clustering as well as heterologously expressed CRAC current. Together with the observation that, unlike 2-APB, the analogue compounds failed to activate CRACM3/Orai3 current in the absence of STIM, our results suggest that inhibition and activation of SOCE/I CRAC by the 2-APB analogues is mediated by STIM.

The inositol 1,4,5-trisphosphate receptor (IP 3 R) in the endoplasmic reticulum mediates calcium signaling that impinges on intracellular processes. IP 3 Rs are allosteric proteins comprising four subunits that form an ion channel activated by binding of IP 3 at a distance. Defective allostery in IP 3 R is considered crucial to cellular dysfunction, but the specific mechanism remains unknown. Here we demonstrate that a pleiotropic enzyme transglutaminase type 2 targets the allosteric coupling domain of IP 3 R type 1 (IP 3 R1) and negatively regulates IP 3 R1-mediated calcium signaling and autophagy by locking the subunit configurations. The control point of this regulation is the covalent posttranslational modification of the Gln2746 residue that transglutaminase type 2 tethers to the adjacent subunit. Modification of Gln2746 and IP 3 R1 function was observed in Huntington disease models, suggesting a pathological role of this modification in the neurodegenerative disease. Our study reveals that cellular signaling is regulated by a new mode of posttranslational modification that chronically and enzymatically blocks allosteric changes in the ligand-gated channels that relate to disease states.L igand-gated ion channels function by allostery that is the regulation at a distance; the allosteric coupling of ligand binding with channel gating requires reversible changes in subunit configurations and conformations (1). Inositol 1,4,5-trisphosphate receptors (IP 3 Rs) are ligand-gated ion channels that release calcium ions (Ca 2+ ) from the endoplasmic reticulum (ER) (2, 3). IP 3 Rs are allosteric proteins comprising four subunits that assemble a calcium channel with fourfold symmetry about an axis perpendicular to the ER membrane. The subunits of three IP 3 R isoforms (IP 3 R1, IP 3 R2, and IP 3 R3) are structurally divided into three domains: the IP 3 -binding domain (IBD), the regulatory domain, and the channel domain (3-6). Fitting of the IBD X-ray structures (7, 8) to a cryo-EM map (9) indicates that the IBD activates a remote Ca 2+ channel by allostery (8); however, the current X-ray structure only spans 5% of each tetramer, such that the mechanism underlying allosteric coupling of the IBD to channel gating remains unknown.The IP 3 R in the ER mediates intracellular calcium signaling that impinges on homeostatic control in various subsequent intracellular processes. Deletion of the genes encoding the type 1 IP 3 R (IP 3 R1) leads to perturbations in long-term potentiation/ depression (3, 10, 11) and spinogenesis (12), and the human genetic disease spinocerebellar ataxia 15 is caused by haploinsufficiency of the IP 3 R1 gene (13-15). Dysregulation of IP 3 R1 is also implicated in neurodegenerative diseases including Huntington disease (HD) (16-18) and Alzheimer's disease (AD) (19)(20)(21)(22). IP 3 Rs also control fundamental cellular processes-for example, mitochondrial energy production (23, 24), autophagy regulation (24-27), ER stress (28), hepatic gluconeogenesis (29), pancreatic exocytosis (30), and macrophag...

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