Interaction of quercetin and its derivatives with Ca2+-ATPase from sarcoplasmic reticulum: Kinetic and molecular modeling studies

Sarcoplasmic reticulum Ca2+-ATPases (SERCAs) regulate cellular calcium homeostasis and are targeted for age-related diseases. Among 14 SERCA mRNA splice variants, SERCA1a is specific to adult fast-twitch skeletal muscle. Quercetin derivatives (monochloropivaloylquercetin (CPQ), IC50 = 195.7 mu M; 2-chloro-1,4-naphthoquinonequercetin (CHNQ), IC50 = 60.3 mu M) were studied for their impact on SERCA1a using molecular modeling and enzyme kinetics. While there were some similarities in kinetic parameters and molecular modeling, the compounds exhibited di-verse actions on SERCA1a. Quercetin reduced activity by 48% at 250 mu M by binding to the cytosolic ATP-binding pocket with increased ATP affinity. CPQ bound near the Ca2+-binding site, possibly altering the transmembrane domain. CHNQ significantly reduced activity by 94% at 250 mu M without binding to substrate sites. It was proposed that CHNQ induced global protein structure changes, inhibiting Ca2+-ATPase activity.