We control the physical interaction and thus functional regulation between integral membrane protein phospholamban (PLB) and sarcoplasmic reticulum Ca-ATPase (SERCA) through adjusting the membrane surface charge. We used EPR to measure the backbone dynamics of TOAC spin-labeled PLB, time-resolved (TR) FRET to measure the interprobe distance between the donor IAEDANS in SERCA and the acceptor Dabcyl in PLB, and NADH-linked ATPase assay to measure PLB's inhibitory function. The cytoplasmic domain of PLB has a net charge of +3 under physiological conditions. When free or bound to SERCA in lipid vesicles, PLB is in equilibrium between an ordered T state and a dynamically disordered R state, as measured by EPR. TR-FRET resolved two interprobe distances between SERCA and PLB. Compared to zwitterionic lipids (DOPC), anionic lipids (DOPS or DOPG) increased the population of the T state, which has the longer interprobe distance between SERCA and PLB, and the inhibition of SERCA's ATPase function. Cationic lipids (DOEPC or DOTAP) decreased the T state population and SERCA inhibition. We conclude that electrostatics can tune the structural and functional dynamics of PLB. The ordered T state is oriented closer to the membrane surface, resulting in a longer SERCA-PLB interprobe distance, and is more inhibitory. The disordered R state is oriented away from the membrane surface, resulting in a shorter SERCA-PLB interprobe distance, and is less inhibitory. Modulating the membrane surface charges provides a new way of investigating the correlation between internal structural dynamics and function of membrane proteins.