Differential Protein‐Protein Interactions Driven by the Arg/Gly389 Single Nucleotide Polymorphisms in the Cardiac Beta‐1 Adrenergic Receptor

Abstract

Activation of the β1 adrenergic receptor (β1AR) increases electrically induced calcium signals and accelerates sequestration of calcium in the myocardium, promoting contraction and relaxation. In humans, Arg389 and Gly389 are common single nucleotide polymorphisms (SNPs) in β1AR. The Arg389 SNP is associated with higher responses to β agonists in terms of cAMP production and contractile force development; in living subjects, it also is coupled with faster response to b blockers with respect to reductions in heart rate and myocardial contractile force. Nevertheless, it is unknown if calcium signals following β1AR activation affects the receptor’s activities and changes in Ca2+‐dependent regulation of β1AR can explain the difference between these polymorphisms. Calmodulin is the ubiquitous transducer of calcium signals and is a limiting factor in cardiomyocytes. We tested the hypothesis that β1AR directly interacts with calmodulin and that the Arg389 and Gly389 SNPs are associated with disparate β1AR‐calmodulin interactions. Using novel fluorescent biosensors developed for β1AR, we identified a novel calmodulin‐binding domain located at the juxtamembranous region of β1AR that encompasses the Arg/Gly389 SNP. The Arg389 SNP is associated with a biphasic interaction with Ca2+/calmodulin. However, the Gly389 SNP is associated with a monophasic interaction with CaM and a ~12‐fold lower affinity than the Arg389 SNP. These kinetic differences correspond to significant variances in the response of β1AR to physiological calmodulin concentrations, peaking at ~50 nM. We also identified that β1AR‐calmodulin interactions are calcium‐dependent, with higher Ca2+ sensitivity of the Arg389 β1AR–CaM interaction over the entire physiological Ca2+ range. These results suggest that calmodulin binding to β1AR is important for its functions and our observed different biochemical properties of these interactions may explain the different responses in subjects carrying the Arg389 vs the Gly389 SNPs.Support or Funding InformationIOER grant 091707 to Q‐KT.