Electronic structure of S2 state of the oxygen-evolving complex of photosystem II studied by PELDOR

► We measured PELDOR between tyrosine and Mn cluster in S2 state of photosystem II. ► Angular dependence of PELDOR signals was detected in oriented membranes. ► Spin projections of Mn ions were directly estimated from the 1.9 Å crystal structure. ► The Mn ion coordinated by H332, D342 and D189 was assigned to be Mn(III). ► Signs of magnetic couplings between the Mn ions were clarified.