A Single Amino Acid Determines the Selectivity and Efficacy of Selective Negative Allosteric Modulators of Ca1.3 L-Type Calcium Channels.

Ca channels with a Ca1.3 pore-forming α subunit have been implicated in both neurodegenerative and neuropsychiatric disorders, motivating the development of selective and potent inhibitors of Ca1.3 versus Ca1.2 channels, the calcium channels implicated in hypertensive disorders. We have previously identified pyrimidine-2,4,6-triones (PYTs) that preferentially inhibit Ca1.3 channels, but the structural determinants of their interaction with the channel have not been identified, impeding their development into drugs. By a combination of biochemical, computational, and molecular biological approaches, it was found that PYTs bind to the dihydropyridine (DHP) binding pocket of the Ca1.3 subunit, establishing them as negative allosteric modulators of channel gating. Site-directed mutagenesis, based on homology models of Ca1.3 and Ca1.2 channels, revealed that a single amino acid residue within the DHP binding pocket (M1078) is responsible for the selectivity of PYTs for Ca1.3 over Ca1.2. In addition to providing direction for chemical optimization, these results suggest that, like dihydropyridines, PYTs have pharmacological features that could make them of broad clinical utility.