Schematic view on possible dimer structures of styrene monooxygenase components. StyA has the same fold as PHBH and the domains were accordingly colored (Montersino et al. 2011, 2013; Schreuder et al. 1988). FAD binding domain in green, substrate binding domain in red, and dimer interface in blue. The three-dimensional structure of StyA from Pseudomonas sp. S12 (PDB ID: 3IHM, Ukaegbu et al. 2010) is shown in a, where the active site clefts of monomers point to the center and no PHBH-like dimer was determined. A modelled StyA-dimer is presented in b. Here the dimer interfaces interact in a flavoprotein hydroxylase mode (Montersino et al. 2013; Schreuder et al. 1988) and a ‘back to back’ situation is shown in which active sites point into the medium. The experimentally solved three-dimensional StyB-structure (PDB ID: 4F07, Morrison et al. 2013) is shown as dimer in (c). Together the structures of a and c were used to generate a model of StyA2B (d) in which two dimer interfaces occur (van den Heuvel et al. 2004). For clarity, only one StyA2B monomer is shown.