Bacteriochlorophyll-containing protein. Molecular models showing two views of the bacteriochlorophyll-containing protein found in the bacterium Prosthecochloris aestuarii. The background view at upper right is rotated sideways from the foreground view. Bacteriochlorophyll is a pigment used by bacteria to carry out photosynthesis, in a similar way to how plants use chlorophyll to photosynthesise. The pigment is not shown here, but would occupy the central space formed by the pink arrows. P. aestuarii is a green sulphur bacterium, found in places like hot springs. The molecular models show sheets and ribbons that show the secondary structure (the shape) of this protein, and the links between the different areas (domains).