Calander Home 2001-2002 2002-2003 Dr. Arwen Pearson Understanding quinone cofactor biogenesis in methylamine dehydrogenase through novel cofactor generation Date: February 24 Time: Noon to 1 Place: BSBE 4-101 Cofactors made from constitutive amino acids in proteins are now known to be relatively common. A number of these involve the generation of quinone cofactors, such as topa quinone in the copper-containing amine oxidases, and lysyltyrosyl quinone in lysyl oxidase. The biogenesis of the quinone cofactor tryptophan tryptophylquinone (TTQ) in methylamine dehydrogenase (MADH) involves the post-translational modification of two constitutive Trp residues (bTrp57 and bTrp108). The modifications to generate TTQ are the addition of two oxygens to the indole ring of bTrp57, and the formation of a covalent cross-link between Ce3 of bTrp57 and Cd1 of bTrp108. The order in which these events occur is unknown. To investigate the role bTrp108 may play in this process, it was mutated to both a His (W108H) and Cys (W108C) residue. For each mutant, the majority of the protein that was isolated contained a biosynthetic intermediate with only one oxygen atom incorporated into bTrp57 and no cross-link with residue b108. This biosynthetic intermediate was inactive and also exhibited weaker subunit-subunit interactions than native MADH. However, in each mutant preparation, a small percentage of the mutant enzyme was active and possessed a functional tryptophylquinone cofactor. In the case of bW108C, this cofactor may be identical to cysteine tryptophylquinone recently described in the bacterial quinohemoprotein amine dehydrogenase. In bW108H, the active cofactor is presumably a histidine tryptophylquinone, which has not been previously described, and represents the synthesis of a novel quinone protein cofactor.