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Phospholamban (PLN) is the endogenous inhibitor of the sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA), the enzyme that regulates cardiac muscle relaxation. In its phosphorylated state (pS16-PLN, pT17-PLN, and pS16pT17-PLN), PLN does not inhibit SERCA. Dysfunctions in SERCA:PLN interactions and in the PLN phosphorylation mechanism have been implicated in cardiac disease, and targeting PLN is becoming a promising avenue for treating cardomyopathies. In this study, we seek to further improve the design therapeutic PLN mutants by optimizing their functional interactions with an endogenous regulatory phosphatase of PLN, protein phosphatase-1 (PP1). PP1 is responsible for PLN dephosphorylation and the transition from its non-inhibitory to inhibitory state. Using a combination of NMR spectroscopy and biochemical assays, correlations will be built between the structural dynamics of promising therapeutic mutants of PLN and their ability to be dephosphorylated by PP1. Additionally, several new mutants of PLN are developed with the goal they will be able to partially inhibit SERCA and also be impervious to dephosphorylation. Insights to these issues will provide better paradigms with which to design therapeutic mutants of PLN for treatment of heart failure, and also demonstrate a model by which an enzyme can be controlled through tuning the allosteric regulation of an inhibitor.