The pyrrole locus is the major orienting factor in ryanodine binding

Area of Science:

• Biochemistry
• Molecular Biology
• Pharmacology

Background:

• Ryanodine modulates intracellular Ca2+ release channels, known as ryanodine receptors.
• Ryanodine analogs can alter channel states, including long-lived subconductance and closed nonconducting states.
• Understanding ryanodine's structure-activity relationship is crucial for its function.

Purpose of the Study:

• To investigate the relationship between the structure of ryanodine isomers and their binding affinity to striated muscle ryanodine receptors.
• To elucidate the role of specific structural features, like the pyrrole group, in ryanodine binding.
• To develop a predictive model for ryanoid binding based on structural orientation.

Main Methods:

• Measurement of dissociation constants for ryanodine, 3-epiryanodine, and 10-ryanodine using rabbit skeletal muscle ryanodine receptors.
• Comparative molecular field analysis (CoMFA) to predict binding interactions.
• Structural analysis of ryanodine isomers and their binding orientation.

Main Results:

• The binding energy loss upon hydrolysis of ryanodine to ryanodol is largely restored by placing the pyrrole carbonyl group at the 3-epi- and 10-positions.
• Comparative molecular field analysis accurately predicted enhanced binding affinities.
• The pyrrole group was identified as a key determinant of ligand binding orientation within the receptor.

Conclusions:

• The pyrrole group dictates the orientation of ryanoid binding within the ryanodine receptor.
• A model is proposed where ryanoids reorient in the binding site, with the pyrrole consistently occupying a specific subsite.
• This model allows for the prediction of binding constants for other ryanoid compounds.