A Mn(II)-Mn(II) center in human prolidase

► Apoprolidase was generated. ► Mn(II) was proven to be the cofactor necessary for prolidase activity. ► A dinuclear Mn(II)-Mn(II) center was identified in active prolidase. ► The Mn(II) ion was demonstrated to be necessary for prolidase structural integrity. ► A conformational modification was detected in the transition apo/holoenzyme.