Emerging Concepts in Ion Channel Biophysics

Emerging Concepts in Ion Channel Biophysics

Thursday Speaker Abstracts

Ryanodine Receptors: Cross Talk between Allosteric and Ligand-binding Domains

Montserrat Samso

Virginia Commonwealth University, Richmond, VA, USA.

The ryanodine receptor (RyR) is an intracellular Ca

release channel with major roles in

skeletal/cardiac muscle contraction and brain signaling. It is the largest ion channel known,

consisting of four equivalent subunits of ~5,000 residues each, an S1-S6 transmembrane domain

organization, and a large and highly allosteric cytoplasmic scaffold formed by ~40

interconnected domains. With a variety of inputs being sensed simultaneously in several

domains, how are these integrated to control the channel’s conductance? Further modulation of

the RyR-mediated Ca

release comes from its supramolecular association into lattices on the

endo/sarcoplasmic reticulum, from its association with FKBP, and in skeletal muscle, from its

interaction with the Cav1.1 complex. The determination of RyR’s atomic structure and in

multiple conformations are starting to provide more solid insight into the molecular mechanisms

of RyR.

Using cryoEM we analyzed the effect that binding of the high affinity, high occupancy ligand

FKBP has on the conformation of the skeletal isoform of RyR, and how this could explain the

higher stability of RyR-FKBP’s closed state. We also analyzed the structure of the alpha-

solenoid domain, encompassing > 500 residues. This allosteric domain adopts different

conformations in the cardiac and skeletal muscle isoforms despite a very similar sequence. In the

skeletal isoform this domain appears to direct the assembly of RyR into lattices and participate in

the relay of the signal coming from the Cav.1 complex. For the cardiac isoform we see instead an

intriguing cross talk between the alpha-solenoid domain and FKBP, which appears to account

more dramatically for the stabilizing effect of FKBP on RyR. In summary, cryoEM enabled to

unveil new mechanisms of RyR allosterism and isoform specialization.

Supported by the American Heart Association grant 14GRNT19660003 and the Muscular

Dystrophy Association grant MDA352845.