InterPro domain: IPR034405

In micro-organisms such as Chlamydomonas , DNA that has been damaged by ultraviolet light can be repaired by blue light-dependent DNA photolyases in a process known as photoreactivation. Two noncovalently bound chromophores are required. FAD is the catalytic chromophore for all photolyases and is essential for photoreactivation. The identity of the second chromophore is often 7,8-didemethyl-8-hydroxy-5-deazariboflavin (FO) [ 1 ].

This family contains the proteins that form part of the biosynthetic pathways of Factor420 (F420) in the form of FO synthase, and menaquinone (vitamin K2). Both perform complex ring formations and are members of the radical S-adenosylmethionine (AdoMet) superfamily of proteins. In the case of the menaquinone synthase enzymes, both the mechanisms of the two enzymes and role of the SAM moiety have been proposed. In mqnC, SAM is stoichiometric, and generates methionine and deoxyadenosine. In mqnE, the deoxyadeonsine moiety is added to the chorismate substrate. Thus, in both cases SAM is stoichometric [ 2 , 3 , 4 ].

1. Critical role of 7,8-didemethyl-8-hydroxy-5-deazariboflavin for photoreactivation in Chlamydomonas reinhardtii. J. Biol. Chem. 285, 32467-75
2. An alternative menaquinone biosynthetic pathway operating in microorganisms. Science 321, 1670-3
3. Menaquinone biosynthesis: formation of aminofutalosine requires a unique radical SAM enzyme. J. Am. Chem. Soc. 135, 15318-21
4. In vitro reconstitution of the radical S-adenosylmethionine enzyme MqnC involved in the biosynthesis of futalosine-derived menaquinone. Biochemistry 52, 4592-4