Na channel reconstructionTRPC3

我々は音や味覚を始め、様々な刺激に応じて細胞膜でCaイオンを透過させて、細胞内へと刺激を伝えている。そこで主役として活躍するのがセンサーを持つチャネルであるTRP channel群である。 これらは、情報伝達物質と結合し、分子内にイオン通路を開いてCaイオンを流入し、細胞内部へと情報を伝達する。その中でもTRPC3は、最も典型的なTRPチャネルに分類され、脳の可塑性・心筋の興奮制御など様々な生理活動に深く関わる。我々はその構造をクライオ画像から9.9Åの分解能で解明した。その構造は中心のタンクとそれを取り巻くアンテナよりなり、TRPC3が様々のタンパク質と結合する有理な構造と思われる。

Abstract from: Journal of Molecular Biology. Volume 367, Issue 2, 23 March 2007, Pages 373-383


The TRPC3 Channel Has a Large Internal Chamber Surrounded by Signal Sensing Antennas

Ogura T, Tong KI, Mio K, Maruyama Y, Kurokawa H, Sato C, Yamamoto M.

Neuroscience Research Institute and Biological Information Research Center, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-4 Umezono, Tsukuba 305-8568, Japan.

Keap1 is a substrate adaptor of a Cullin 3-based E3 ubiquitin ligase complex that recognizes Nrf2, and also acts as a cellular sensor for xenobiotics and oxidative stresses. Nrf2 is a transcriptional factor regulating the expression of cytoprotective enzyme genes in response to such stresses. Under unstressed conditions Keap1 binds Nrf2 and results in rapid degradation of Nrf2 through the proteasome pathway. In contrast, upon exposure to oxidative and electrophilic stress, reactive cysteine residues in intervening region (IVR) and Broad complex, Tramtrack, and Bric-à-Brac domains of Keap1 are modified by electrophiles. This modification prevents Nrf2 from rapid degradation and induces Nrf2 activity by repression of Keap1. Here we report the structure of mouse Keap1 homodimer by single particle electron microscopy. Three-dimensional reconstruction at 24-Å resolution revealed two large spheres attached by short linker arms to the sides of a small forked-stem structure, resembling a cherry-bob. Each sphere has a tunnel corresponding to the central hole of the beta-propeller domain, as determined by x-ray crystallography. The IVR domain appears to surround the core of the beta-propeller domain. The unexpected proximity of IVR to the beta-propeller domain suggests that any distortions generated during modification of reactive cysteine residues in the IVR domain may send a derepression signal to the beta-propeller domain and thereby stabilize Nrf2. This study thus provides a structural basis for the two-site binding and hinge-latch model of stress sensing by the Nrf2-Keap1 system.

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