Derivative manipulation in the structure solution of the integral membraneLH2 complex

The structure of the peripheral light-harvesting complex from Rhodopseudomo nas acidophila strain 10050 was determined by multiple isomorphous replacem ent methods. The derivatization of the crystals was augmented by the additi on of a backsoaking stage. The soak/backsoaked data comparison had greater isomorphism and showed simpler Patterson maps than the standard native/soak comparison. Amplitudes from the derivatized then backsoaked crystals and f rom the derivatized crystals were compared in order to extract a subset of heavy-atom sites. Using this information, the full array of sites were foun d from a derivative/native comparison, eventually leading to excellent elec tron-density maps.