Cryogenic structure of the photosynthetic reaction center of Blastochloris viridis in the light and dark.

The structure of the Blastochloris viridis photosynthetic reaction center has been determined at 100 K by flash-freezing crystals. A data set to 2.2 A resolution provides a well determined model of the wild-type protein. Of particular interest are the position, occupancy and heterogeneity of the Q(B)-binding site. Data were also collected from a crystal frozen immediately after illumination. The data support predominant binding of Q(B) in the proximal position in both the neutral and charge-separated states.