Three-dimensional rearrangements within inositol 1,4,5-trisphosphate receptor by calcium.
Allosteric binding of calcium ion (Ca2+) to inositol 1,4,5-trisphosphate (IP3) receptor (IP3R) controls channel gating within IP3R. Here, we present biochemical and electron microscopic evidence of Ca2+-sensitive structural changes in the three-dimensional structure of type 1 IP3R (IP3R1). Low concentrations of Ca2+ and high concentrations of Sr2+ and Ba2+ were shown to be effective for the limited proteolysis of IP3R1, but Mg2+ had no effect on the proteolysis. The electron microscopy and the limited proteolysis consistently demonstrated that the effective concentration of Ca2+ for conformational changes in IP3R1 was <10(-7) m and that the IP3 scarcely affected the conformational states. The structure of IP3R1 without Ca2+, as reconstructed by three-dimensional electron microscopy, had a "mushroom-like" appearance consisting of a large square-shaped head and a small channel domain linked by four thin bridges. The projection image of the "head-to-head" assembly comprising two particles confirmed the mushroom-like side view. The "windmill-like" form of IP3R1 with Ca2+ also contains the four bridges connecting from the IP3-binding domain toward the channel domain. These data suggest that the Ca2+-specific conformational change structurally regulates the IP3-triggered channel opening within IP3R1.
Laboratory for Developmental Neurobiology, Brain Science Institute, RIKEN (The Institute of Physical and Chemical Research), 2-1 Hirosawa, Wako, Saitama, 351-0198, Japan. hamada@ims.u-tokyo.ac.jp
Kozo
K
Hamada
Akiko
A
Terauchi
Katsuhiko
K
Mikoshiba
D000495:Allosteric Site; D000818:Animals; D016367:Baculoviridae / Q000378:metabolism; D001464:Barium / Q000737:chemistry; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry* / Q000378:metabolism; D015220:Calcium Channels / Q000737:chemistry*; D002412:Cations; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D007091:Image Processing, Computer-Assisted; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007313:Insecta; D008274:Magnesium / Q000737:chemistry; D008854:Microscopy, Electron; D008861:Microsomes / Q000378:metabolism; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry*; D011994:Recombinant Proteins / Q000737:chemistry; D013324:Strontium / Q000737:chemistry
D015220:Calcium Channels; D002412:Cations; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D011994:Recombinant Proteins; D001464:Barium; D008274:Magnesium; D002118:Calcium; D013324:Strontium