Subunit B of the Class III Extradiol dioxygenase, Protocatechuate 4,5-dioxygenase, and simlar enzymes.
This subfamily of class III extradiol dioxygenases consists of a number of proteins with known enzymatic activities: Protocatechuate (PCA) 4,5-dioxygenase (LigAB), 2,3-dihydroxyphenylpropionate 1,2-dioxygenase (MhpB), 3-O-Methylgallate Dioxygenase, 2-aminophenol 1,6-dioxygenase, as well as proteins without any known enzymatic activity. These proteins play essential roles in the degradation of aromatic compounds by catalyzing the incorporation of both atoms of molecular oxygen into their preferred substrates. As members of the Class III extradiol dioxygenase family, the enzymes use a non-heme Fe(II) to cleave aromatic rings between a hydroxylated carbon and an adjacent non-hydroxylated carbon. LigAB-like class III enzymes are usually composed of two subunits, designated A and B, which form a tetramer composed of two copies of each subunit. This model represents the catalytic subunit, B.