Structure, function and biogenesis of proteins catalysing respiratory and transport processes in the N-cycle
Co-workers: Dr Julie Stevens, Dr Shilpa Bali, Dr Despoina Mavridou, Paraskevi Kritsiligkou, Yulin Zhang
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. In collaboration with colleagues in Molecular Biophysics 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 nadequate 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 ransmembrane 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.
- Mavridou DAI, Stevens JM, Goddard AD, Willis AC, Ferguson SJ and Redfield C (2009) Control of periplasmic interdomain thiol:disulfide exchange in the transmembrane oxidoreductase DsbD. J. Biol Chem 284, 3219-3226
- Harvat EM, Redfield C, Stevens JM and Ferguson SJ (2009) Probing the heme-binding site of the cytochrome c maturation protein CcmE. Biochemistry 48, 1820-1828
- Goddard AD, Moir JWB, Richardson DJ and Ferguson SJ (2008) Interdependence of two Nark domains in a fused nitrate/nitrite transporter. Molecular Microbiology 70, 667-681
- Sam KA, Strampraad MJF, de Vries S, and Ferguson SJ (2008) Very early reaction intermediates detected by microsecond time scale kinetics of cytochrome cd1-catalyzed reduction of nitrite. J. Biol. Chem. 283, 27403-27409
- Allen JW, Harvat EM, Stevens JM and Ferguson SJ (2006) A variant System I for cytochrome c biogenesis in archaea and some bacteria has a novel CcmE and no CcmH. FEBS Lett 580: 4827
Figure 1: Cytochrome cd1 nitrite reductase
Figure 2: The Nitrogen Cycle
Figure 3: NMR studies of cDsbD (with Dr Christina Redfield - Cover figure on the 20 July 2007 issue of the Journal of Molecular Biology)
Figure 4: Cytochrome c maturation system in E. coli
Figure 5: Redox potentiometry of a heme-containing protein