Two-state conformational changes in inositol 1,4,5-trisphosphate receptor regulated by calcium.
Inositol 1,4,5-trisphosphate receptor (IP3R) is a highly controlled calcium (Ca2+) channel gated by inositol 1,4,5-trisphosphate (IP3). Multiple regulators modulate IP3-triggered pore opening by binding to discrete allosteric sites within IP3R. Accordingly we have postulated that these regulators structurally control ligand gating behavior; however, no structural evidence has been available. Here we show that Ca2+, the most pivotal regulator, induced marked structural changes in the tetrameric IP3R purified from mouse cerebella. Electron microscopy of the IP3R particles revealed two distinct structures with 4-fold symmetry: a windmill structure and a square structure. Ca2+ reversibly promoted a transition from the square to the windmill with relocations of four peripheral IP3-binding domains, assigned by binding to heparin-gold. Ca2+-dependent susceptibilities to limited digestion strongly support the notion that these alterations exist. Thus, Ca2+ appeared to regulate IP3 gating activity through the rearrangement of functional domains.
Hamada
Kozo
K
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
Miyata
Tomoko
T
Mayanagi
Kouta
K
Hirota
Junji
J
Mikoshiba
Katsuhiko
K
D000495:Allosteric Site; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000737:chemistry* / Q000378:metabolism; D002531:Cerebellum / Q000648:ultrastructure; D006046:Gold / Q000737:chemistry; D006493:Heparin / Q000737:chemistry; D053496:Inositol 1,4,5-Trisphosphate Receptors; D051379:Mice; D008854:Microscopy, Electron; D008954:Models, Biological; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry* / Q000378:metabolism
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D006046:Gold; D006493:Heparin; D002118:Calcium