Crystallographic Study of a Quinoprotein Electron Transfer System: Methylamine Dehydrogenase

Washington University School Of Medicine, Saint Louis MO

Investigators

Abstract

Electron transfer between biological macromolecules usually occurs within a transient complex in which the participating redox centers and the intervening protein are optimally configured to promote and regulate electron flow between the centers. Only a few such complexes have been crystallized. Methylamine dehydrogenase (MADH) and amicyanin, both together and with a cytochrome, form two structurally characterized physiological electron transfer complexes; the complex of aromatic amine dehydrogenase (AADH) with azurin comprises a third. MADH and AADH, as well as quinohemoprotein amine dehydrogenase (QHNDH), catalyze the oxidative deamination of primary amines. All three enzymes contain the redox cofactor tryptophylquinone (TRQ), a tryptophan side chain containing two quinone oxygen atoms. TRQ is crosslinked to another tryptophan in MADH and AADH or to a cysteine in QHNDH. The aims of this project are to carry out structural studies of (1) amicyanin mutants with altered redox properties, alone and in complex with MADH, (2) redox variants and ligand-bound forms of the AADH/azurin complex and (3) the roles and biogenesis of TRQ and its crosslink to cysteine in QHNDH. The results will help identify structural features important for modulation of biological electron transfer, including partner recognition, regulation of driving force, reorganization energy and gating. The studies of TRQ biogenesis are important because of the ubiquity in biology of posttranslationally modified amino acid side chains whose roles and biogenic mechanisms are poorly understood. The broader impacts resulting from the proposed activity will include the promotion of undergraduate training in research both nationally and internationally. Efforts to involve local undergraduates in the structural studies will continue and single crystal spectroscopic studies of electron transfer complexes in Italy will provide a training environment for students abroad. The research will also enhance research infrastructure through international partnerships with scientists and their students in Japan and Italy.