Abstract
Ryanodine receptor 1 (RyR1) is an intracellular calcium ion (Ca2+)
release channel required for skeletal muscle contraction. Although
cryo-electron microscopy identified binding sites of three coactivators
Ca2+, ATP and caffeine (CFF), the mechanism of co-regulation and synergy
of these activators is unknown. Here, we report allosteric connections
among the three ligand binding sites and pore region in (i) Ca2+
bound-closed, (ii) ATP/CFF bound- closed, (iii) Ca2+/ATP/CFF
bound-closed, and (iv) Ca2+/ATP/CFF bound-open RyR1 states. We
identified two dominant interactions that mediate interactions between
the Ca2+ binding site and pore region in Ca2+ bound-closed state, which
partially overlapped with the pore communications in ATP/CFF
bound-closed RyR1 state. In Ca2+/ATP/CFF bound-closed and -open RyR1
states, co-regulatory interactions were analogous to communications in
the Ca2+ bound-closed and ATP/CFF bound- closed states. Both ATP- and
CFF- binding sites mediate communication between the Ca2+ binding site
and the pore region in Ca2+/ATP/CFF bound - open RyR1 structure. We
conclude that Ca2+, ATP, and CFF propagate their effects to the pore
region through a network of overlapping interactions that mediate
allosteric control and molecular synergy in channel regulation.