TRPV4 channel activity is modulated by direct interaction of the ankyrin domain to PI(4,5)P2

[プレスリリース]バイオサイエンス研究科分子医学細胞生物学研究室の末次志郎教授らの研究グループが生理的に重要なイオンを運ぶ通り道TRPV4の新たな制御機構を解明（2014/09/29）Mutations in the ankyrin repeat domain (ARD) of ​TRPV4 are responsible for several channelopathies, including Charcot–Marie–Tooth disease type 2C and congenital distal and scapuloperoneal spinal muscular atrophy. However, the molecular pathogenesis mediated by these mutations remains elusive, mainly due to limited understanding of the ​TRPV4 ARD function. Here we show that phosphoinositide binding to the ​TRPV4 ARD leads to suppression of the channel activity. Among the phosphoinositides, phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) most potently binds to the ​TRPV4 ARD. The crystal structure of the ​TRPV4 ARD in complex with ​inositol-1,4,5-trisphosphate, the head-group of PI(4,5)P2, and the molecular-dynamics simulations revealed the PI(4,5)P2-binding amino-acid residues. The ​TRPV4 channel activities were increased by titration or hydrolysis of membrane PI(4,5)P2. Notably, disease-associated ​TRPV4 mutations that cause a gain-of-function phenotype abolished PI(4,5)P2 binding and PI(4,5)P2 sensitivity. These findings identify ​TRPV4 ARD as a lipid-binding domain in which interactions with PI(4,5)P2 normalize the channel activity in ​TRPV4

Phagocytosis is mediated by two-dimensional assemblies of the F-BAR protein GAS7

Phagocytosis is a cellular process for internalization of micron-sized large particles including pathogens. The Bin-Amphiphysin-Rvs167 (BAR) domain proteins, including the FCH-BAR (F-BAR) domain proteins, impose specific morphologies on lipid membranes. Most BAR domain proteins are thought to form membrane invaginations or protrusions by assembling into helical submicron-diameter filaments, such as on clathrin-coated pits, caveolae, and filopodia. However, the mechanism by which BAR domain proteins assemble into micron-scale phagocytic cups was unclear. Here, we show that the two-dimensional sheet-like assembly of Growth Arrest-Specific 7 (GAS7) plays a critical role in phagocytic cup formation in macrophages. GAS7 has the F-BAR domain that possesses unique hydrophilic loops for two-dimensional sheet formation on flat membranes. Super-resolution microscopy reveals the similar assemblies of GAS7 on phagocytic cups and liposomes. The mutations of the loops abolishes both the membrane localization of GAS7 and phagocytosis. Thus, the sheet-like assembly of GAS7 plays a significant role in phagocytosis