Conformational motions and ligand-binding underlying gating and regulation in IPR channel.

Inositol-1,4,5-trisphosphate receptors (IPRs) are activated by IP and Ca and their gating is regulated by various intracellular messengers that finely tune the channel activity. Here, using single particle cryo-EM analysis we determined 3D structures of the nanodisc-reconstituted IPR1 channel in two ligand-bound states. These structures provide unprecedented details governing binding of IP, Ca and ATP, revealing conformational changes that couple ligand-binding to channel opening.

Cryo-EM structure of type 1 IPR channel in a lipid bilayer.

Type 1 inositol 1,4,5-trisphosphate receptor (IPR1) is the predominant Ca-release channel in neurons. IPR1 mediates Ca release from the endoplasmic reticulum into the cytosol and thereby is involved in many physiological processes. Here, we present the cryo-EM structures of full-length rat IPR1 reconstituted in lipid nanodisc and detergent solubilized in the presence of phosphatidylcholine determined in ligand-free, closed states by single-particle electron cryo-microscopy.

Activation of C3a receptor is required in cigarette smoke-mediated emphysema.

Exposure to cigarette smoke can initiate sterile inflammatory responses in the lung and activate myeloid dendritic cells (mDCs) that induce differentiation of T helper type 1 (Th1) and Th17 cells in the emphysematous lungs. Consumption of complement proteins increases in acute inflammation, but the contribution of complement protein 3 (C3) to chronic cigarette smoke-induced immune responses in the lung is not clear. Here, we show that following chronic exposure to cigarette smoke, C3-deficient (C3(-/-)) mice develop less emphysema and have fewer CD11b(+)CD11c(+) mDCs infiltrating the lungs as compared with wild-type mice.

Agonistic induction of PPARγ reverses cigarette smoke-induced emphysema.

The development of emphysema in humans and mice exposed to cigarette smoke is promoted by activation of an adaptive immune response. Lung myeloid dendritic cells (mDCs) derived from cigarette smokers activate autoreactive Th1 and Th17 cells. mDC-dependent activation of T cell subsets requires expression of the SPP1 gene, which encodes osteopontin (OPN), a pleiotropic cytokine implicated in autoimmune responses.