Two versatile cofactors, flavin adenine dinucleotide and non-heme iron, involved in DNA repair and natural product halogenation

Abstract

Cofactors assist enzymes with a variety of complex chemistries. Two versatile cofactors, flavin adenine dinucleotide (FAD) and non-heme iron, together with molecular oxygen as an oxidizing agent, perform a wide array of reactions. Hydroxylation in DNA repair is one example. AidB is an adaptive response protein that is up-regulated in the presence of alkylating agents. AidB contains FAD; however, the precise role of the FAD has been determined. AlkB, another adaptive response protein that is up-regulated in the presence of alkylating agents, is a member of the alpha-ketoglutarate (aKG) non-heme iron-dependent superfamily. It uses the cofactor non-heme iron, and the co-substrates molecular oxygen a: G, to remove alkylated adducts on DNA bases via hydroxylation. Two well characterized 1 homologues of AlkB, hABH2 and hABH3, also belong to the XKG/Fe(II)-dependent superfamily, but their substrate preference differ from that of AlkB. Furthermore, FAD and non-heme iron, again with molecular oxygen as an oxidizing agent, can perform halogenation chemistry. Flavin-dependent halogenasess perform halogenation reactions on aromatic substrates, while non-heme iron-dependent halogenases perform halogenations reactions on unactivated aliphatic substrates. I is a flavin-dependent halogenase that catalyzes the chlorination of free tryptophan to form 7-chlorotryptophan in the biosynthesis of rebeccamycin. CytC3 is an cxKG and non-heme iron-dependent halogenase that catalyzes the chlorination of L-2-aminobutyric acid bound to thiolation domain in the biosynthesis of yy-dichloroaminobutyrate.

(cont.) Here, we obtained the crystal structures of flavoproten I and non-heme iron-dependent halogenase CytC3. The structural and biochemical v n AidB provides new insights into various possible functions of this still poorly understood protein. The crystal structure of CytC3 suggests two important criteria for creating an enzyme--bound Fe-Cl catalyst. Additionally, we established a new purification scheme for AlkB ts human homologues, which has yielded protein for biochemical studies aimed at ex i ; substrate specificity. Finally, we have also obtained a new crystal form for E. coli AlkB.