Coupling of agonist binding to channel gating in an ACh-binding protein linked to an ion channel.
Neurotransmitter receptors from the Cys-loop superfamily couple the binding of agonist to the opening of an intrinsic ion pore in the final step in rapid synaptic transmission. Although atomic resolution structural data have recently emerged for individual binding and pore domains, how they are linked into a functional unit remains unknown. Here we identify structural requirements for functionally coupling the two domains by combining acetylcholine (ACh)-binding protein, whose structure was determined at atomic resolution, with the pore domain from the serotonin type-3A (5-HT3A) receptor. Only when amino-acid sequences of three loops in ACh-binding protein are changed to their 5-HT3A counterparts does ACh bind with low affinity characteristic of activatable receptors, and trigger opening of the ion pore. Thus functional coupling requires structural compatibility at the interface of the binding and pore domains. Structural modelling reveals a network of interacting loops between binding and pore domains that mediates this allosteric coupling process.
Instituto de Investigaciones Bioquimicas, UNS-CONICET, Bahia Blanca 8000, Argentina.
Cecilia
C
Bouzat
Fernanda
F
Gumilar
Guillermo
G
Spitzmaul
Hai-Long
HL
Wang
Diego
D
Rayes
Scott B
SB
Hansen
Palmer
P
Taylor
Steven M
SM
Sine
D000109:Acetylcholine / Q000378:metabolism*; D000494:Allosteric Regulation; D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000819:agonists* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D004553:Electric Conductivity; D015640:Ion Channel Gating / Q000187:drug effects*; D007473:Ion Channels / Q000819:agonists* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008564:Membrane Potentials; D008958:Models, Molecular; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D051381:Rats; D044406:Receptors, Serotonin, 5-HT3 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000819:agonists / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D058827:Serotonin 5-HT3 Receptor Agonists
D002352:Carrier Proteins; D007473:Ion Channels; D044406:Receptors, Serotonin, 5-HT3; D011993:Recombinant Fusion Proteins; D058827:Serotonin 5-HT3 Receptor Agonists; D000109:Acetylcholine