Three-dimensional location of the imperatoxin A binding site on the ryanodine receptor

Cryo-electron microscopy and three-dimensional, single-particle image analy sis have been used to reveal the specific binding site of imperatoxin A (Ip Tx(a)) on the architecture of the calcium release channel/ryanodine recepto r from skeletal muscle (RyR1). IpTx(a) is a peptide toxin that binds with h igh affinity to RyR1 and affects its functioning. The toxin was derivatized with biotin to enhance its detection with streptavidin, IpTx(a), binds to the cytoplasmic moiety of RyR1 between the clamp and handle domains, 11 nm away from the trans- membrane pore. The proposed mimicry by IpTx(a) of the dihydropyridine receptor (DHPR) II-III loop, thought to be a main physiolog ical excitation-contraction trigger, suggests that the IpTx(a) binding loca tion is a potential excitation-contraction signal transduction site.