Silveira, CM, Castro MA, Dantas JM, Salgueiro C, Murgida DH, Todorovic S.
2017.
Structure, electrocatalysis and dynamics of immobilized cytochrome PccH and its microperoxidase, 2017. Physical Chemistry Chemical Physics. 19(13):8908-8918.: The Royal Society of Chemistry
AbstractGeobacter sulfurreducens cells have the ability to exchange electrons with conductive materials, and the periplasmic cytochrome PccH plays an essential role in the direct electrode-to-cell electron transfer in this bacterium. It has atypically low redox potential and unique structural features that differ from those observed in other c-type cytochromes. We report surface enhanced resonance Raman spectroscopic and electrochemical characterization of the immobilized PccH, together with molecular dynamics simulations that allow for the rationalization of experimental observations. Upon attachment to electrodes functionalized with partially or fully hydrophobic self-assembled monolayers, PccH displays a distribution of native and non-native heme spin configurations, similar to those observed in horse heart cytochrome c. The native structural and thermodynamic features of PccH are preserved upon attachment mixed hydrophobic (-CH3/-NH2) surfaces, while pure -OH, -NH2 and -COOH surfaces do not provide suitable platforms for its adsorption, indicating that its still unknown physiological redox partner might be membrane integrated. Neither of the employed immobilization strategies results in electrocatalytically active PccH capable of the reduction of hydrogen peroxide. Pseudoperoxidase activity is observed in immobilized microperoxidase, which is enzymatically produced from PccH and spectroscopically characterized. Further improvement of PccH microperoxidase stability is required for its application in electrochemical biosensing of hydrogen peroxide.
Pokkuluri, PR, Pessanha M, Londer YY, Wood SJ, Duke NEC, Wilton R, Catarino T, Salgueiro CA, Schiffer M.
2008.
Structures and Solution Properties of Two Novel Periplasmic Sensor Domains with c-Type Heme from Chemotaxis Proteins of Geobacter sulfurreducens: Implications for Signal Transduction. Journal of Molecular Biology. 377(5):1498-1517.
AbstractPeriplasmic sensor domains from two methyl-accepting chemotaxis proteins from Geobacter sulfurreducens (encoded by genes GSU0935 and GSU0582) were expressed in Escherichia coli. The sensor domains were isolated, purified, characterized in solution, and their crystal structures were determined. In the crystal, both sensor domains form swapped dimers and show a PAS-type fold. The swapped segment consists of two helices of about 45 residues at the N terminus with the hemes located between the two monomers. In the case of the GSU0582 sensor, the dimer contains a crystallographic 2-fold symmetry and the heme is coordinated by an axial His and a water molecule. In the case of the GSU0935 sensor, the crystals contain a non-crystallographic dimer, and surprisingly, the coordination of the heme in each monomer is different; monomer A heme has His-Met ligation and monomer B heme has His-water ligation as found in the GSU0582 sensor. The structures of these sensor domains are the first structures of PAS domains containing covalently bound heme. Optical absorption, electron paramagnetic resonance and NMR spectroscopy have revealed that the heme groups of both sensor domains are high-spin and low-spin in the oxidized and reduced forms, respectively, and that the spin-state interconversion involves a heme axial ligand replacement. Both sensor domains bind NO in their ferric and ferrous forms but bind CO only in the reduced form. The binding of both NO and CO occurs via an axial ligand exchange process, and is fully reversible. The reduction potentials of the sensor domains differ by 95 mV (− 156 mV and − 251 mV for sensors GSU0582 and GSU0935, respectively). The swapped dimerization of these sensor domains and redox-linked ligand switch might be related to the mechanism of signal transduction by these chemotaxis proteins.