Received for publication January 12, 2006.
Revised April 4, 2006.
Accepted for publication April 6, 2006.

Structural determinants of 4-chloro-m-cresol required for activation of ryanodine receptor type 1

Abstract

4-Chloro-m-cresol (4-CmC) is a clinically relevant activator of the intracellular Ca²⁺ release channel, the ryanodine receptor isoform 1 (RyR1). In this study, the chemical moieties on the 4-CmC molecule required for its activation of RyR1 were determined using structure-activity relationship analysis with a set of commercially available 4-CmC analogs. Separate compounds each lacking one of the three functional groups of 4-CmC (1-hydroxyl, 3-methyl, 4-chloro) were poor activators of RyR1. Substitution of different chemical groups for the 1-hydroxyl of 4-CmC resulted in compounds that were poor activators of RyR1, thus suggesting that the hydroxyl group is preferred at this position. Substitution of hydrophobic groups at the 3-position enhanced bioactivity of the compound relative to 4-CmC, whereas substitution with hydrophilic groups abolished bioactivity. Similarly, 4-CmC analogs with hydrophobic groups substituted into the 4-position enhanced bioactivity while hydrophilic or charged groups diminished bioactivity. 4-CmC analogs containing a single hydrophobic group at either the 3- or 4- position as well as 3,5-disubstituted or 3,4,5-trisubstituted phenols were also effective activators of RyR1. These results indicate that the 1-hydroxyl group of 4-CmC is required for activation of RyR1 and that hydrophobic groups at the 3,4 and 5-positions are preferred. These findings suggest that the 4-CmC binding site on RyR1 most likely consists of a hydrophilic region to interact with the 1-hydroxyl as well as a hydrophobic region(s) to interact with chemical groups at the 3- and/or 4- positions of 4-CmC

Key words: Structure-activity relationships and modeling, Ca imaging, Receptor binding studies