Three-dimensional structure of the alpha1-beta complex in the skeletal muscle dihydropyridine receptor by single-particle electron microscopy.
The dihydropyridine receptor (DHPR) is a protein complex that consists of five distinct subunits of alpha(1), alpha(2), beta, gamma and delta and functions as a voltage-dependent L-type Ca(2+) channel. Here we purified the alpha(1)-beta complex (approximately 250 kDa) from the rabbit skeletal muscle DHPR and reconstructed its three-dimensional (3D) structure to 38 A resolution by single particle analysis of negative staining electron microscopy. The alpha(1)-beta structure exhibited two unique regions: a pseudo-4-fold petaloid region and an elongated region. X-ray crystallographic models of a homologous voltage-dependent K(+) channel and the beta subunit fit well into the individual regions of the alpha(1)-beta structure, revealing that the two regions correspond to the transmembrane alpha(1) and the cytoplasmic beta subunits, respectively. In addition, 3D reconstruction and immuno-electron microscopic analysis performed on the independently purified DHPR demonstrated that the alpha(1)-beta complex was located in the large globular portion of the DHPR, and the N-terminal region of the beta subunit was extended to the leg-shaped protrusion of the DHPR, which includes the alpha(2)delta subunits. Our results propose a model in which the beta subunit may regulate ion channel function by acting as a hinge between alpha(1) and alpha(2)delta subunits of the DHPR.
Murata
Kazuyoshi
K
Japan Biological Information Research Center, AIST Tokyo Waterfront, 2-41-6 Aomi, Koto-ku, Tokyo 135-0064, Japan. kazum6@gmail.com
Nishimura
Shinpei
S
Kuniyasu
Akihiko
A
Nakayama
Hitoshi
H
D000818:Animals; D020746:Calcium Channels, L-Type / Q000737:chemistry* / Q000302:isolation & purification / Q000648:ultrastructure*; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D008854:Microscopy, Electron / Q000379:methods*; D018482:Muscle, Skeletal / Q000737:chemistry; D011817:Rabbits
D020746:Calcium Channels, L-Type