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 Å 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.