This bacterial enzyme binds two [4Fe-4S] clusters [2,3]. A bridge of five sulfur atoms is formed between the free Fe atoms of the two [4Fe-4S] clusters [6]. In the first reaction the enzyme transfers a methyl group from AdoMet to the external sulfur ion of the sulfur bridge. In the second reaction the enzyme catalyses the reductive fragmentation of a second molecule of AdoMet, yielding a 5′-deoxyadenosine radical, which then attacks the methylated sulfur atom of the polysulfide bridge, resulting in the transfer of a methylsulfanyl group to aspartate89?[5,6]. The enzyme is a member of the superfamily of?S-adenosyl-L-methionine-dependent radical (radical AdoMet) enzymes.
![Example Structure of [ribosomal protein S12] (aspartate89-C3)-methylthiotransferase EC#: 2.8.4.4](/wp-content/uploads/enzyme-structure/2.8.4.4.jpg)