Campylobacter jejuni Periplasmic Nitrate Reductase NapA as a Medium for Elucidating Molybdenum Cofactor Reactivity

Abstract

Periplasmic nitrate reductase NapA is found within many gram-negative bacteria and catalyzes oxygen atom transfer reactions. NapA utilizes nitrate as a terminal electron acceptor in place of oxygen in low-air conditions, such as in the human gastrointestinal tract. Within the scope of this thesis, NapA from Campylobacter jejuni is primarily focused due to its reputation in poultry husbandry and antibiotic resistance. Although nitrate reduction aids in pathogen survival, it is also a geochemically essential process. Many enzymes closely related to NapA are involved in geochemical cycling and contain the same active site ligand structure. The ligand within these enzymes is called molybdenum cofactor, or Moco. The structure of the enzyme is influential on reactivity of the molybdenum cofactor. The rate of catalysis, electron and proton transfer, and substrate preference can be affected by the amino acids surrounding Moco. Elucidating details of Moco reactivity aids in understanding bacteria in relation to human health and geochemical cycles. The primary tools throughout this research were site-directed mutagenesis and steady-state kinetics.