The Pyrrole Locus Is the Major Orienting Factor in Ryanodine Binding

Abstract

Ryanodine, a natural product, is a complex modulator of a class of intracellular Ca2+ release channels commonly called the ryanodine receptors. Ryanodine analogs can cause the channel to persist in long-lived, subconductance states or, at high ligand concentrations, in closed, nonconducting states. In this paper, we further explore the relationship between structure and ryanodine binding to striated muscle. Ryanodine, 3-epiryanodine, and 10-ryanodine are three structural isomers of ryanodine. The dissociation constants of these compounds were measured using rabbit skeletal muscle ryanodine receptors. Placing the pyrrole carbonyl group at the 3-epi- and 10-positions of ryanodol largely restores the large loss of binding energy observed when ryanodine is hydrolyzed to ryanodol. Comparative molecular field analysis successfully predicts the enhanced binding and indicates that the pyrrole group controls the orientation of ligand binding. We propose that the ryanoids are reorientated in the binding site of the ryanodine receptors such that the pyrrole always occupies the same subsite. By applying this model, the binding constants of other ryanoids are predicted.

Streptozotocin-Induced Diabetes Increases Disulfide Bond Formation on Cardiac Ryanodine Receptor (RyR2)

“…In the case of RyR2, which has Ϸ84 free SH residues (Ն360 cysteine residues total), oxidation of these groups will alter the activity of the channel (either increasing or decreasing activity). We and others have also shown that the pyrrole moiety is an essential determinant for ryanodine to bind to RyR1 (Welch et al, 1996;Bidasee and Besch, 1998). With these two pieces of information, we rationalized that a sulfhydryl reagent containing a pyrrole moiety might be useful to probe the oxidative state of cysteine residues in proximity to (or within) the vicinity of the ryanodine binding site(s) on RyR2.…”

Functional Characterization of Mutants in the Predicted Pore Region of the Rabbit Cardiac Muscle Ca2+ Release Channel (Ryanodine Receptor Isoform 2)

“…The binding site has been localized to the COOH-terminal region in the linear sequence in biochemical studies (18,19). Studies with ryanoids have predicted that pyrrole and isopropyl groups are embedded deep inside a cleft in RyR molecules (39).…”

Structure-Function Relationships among Ryanodine Derivatives

“…2d, ©) would be only 3-fold less than that of ryanodine (OE) because a recent study proposed overwhelming dominance of the pyrrole for binding affinity (36). The present data (especially those on potency and efficacy, see below) suggest that the six-membered C 3 substituent of pyridyl ryanodine is accommodated almost equally well as the five-membered substituent of ryanodine.…”