Structure function and biogenesis of bacterial respiratory proteins
Bacterial respiratory pathways are diverse and complex and include cytochromes c and a variety of metalloenzymes. Our work aims to understand the assembly of these cofactor-containing proteins and how they function. We obtained the crystal structure of the bacterial respiratory enzyme nitrite reductase. This enzyme is involved in the nitrogen cycle in the process of denitrification, which, if occurring at inadequate rates will have adverse effects on the environment (eg. high levels of nitrate in soil or release of nitrous oxide into the atmosphere). A major group of respiratory proteins, the c-type cytochromes, contain covalently linked heme groups. The attachment of the heme to the protein is complex and involves many proteins, including transmembrane transport proteins and proteins that function in disulphide bond isomerisation. Proteins involved in disulphide bond formation are of particular significance because many extracellular bacterial toxins contain disulphide bonds and it is therefore important to understand the mechanisms by which these bonds form. In Gram-negative bacteria the protein and the heme cofactor must be transported to the periplasm for the c-type cytochrome assembly process. It is not known how the heme is transported across the membrane or how it becomes attached to the cytochrome polypeptide. Another perplexing transport event in the N-cycle is how nitrate and nitrite used in respiration respectively enter and exit the cell. We employ an array of methodologies to study the respiratory proteins and the processes involved in their assembly.