Figure 2.

Homology models of class B scavenger receptor and carotenoid cleavage dioxygenases. a) Extracellular domain model of human SCARB1 receptor with proposed lipid entering and exiting tunnel highlighted with a grey color mesh b) Structure alignment of BCO1 and BCO2 homology model (RMSD ~ 0.1 Å), BCO1 is shown with cyan and BCO2 is shown with purple color. The enzymes’ substrate tunnel is shown as grey color mesh. c) Active site of BCO2 with parts of the substrate-binding cavity is displayed as grey color mesh. The active center contains a ferrous iron (highlighted in red color) that is coordinated by four conserved histidine residues (green) and glutamate residues (sky blue). Additionally, aromatic side amino side chains are highlighted that interact with the carotenoid substrates.