Molecular interactions between Geobacter sulfurreducens triheme cytochromes and the redox active analogue for humic substances

摘要: The bacterium Geobacter sulfurreducens can transfer electrons to quinone moieties of humic substances or anthraquinone-2,6-disulfonate (AQDS), a model for the acids. reduced form AQDS (AH2QDS) also be used as energy source by G. sulfurreducens. Such bidirectional utilization confers competitive advantages these bacteria in Fe(III) enriched environments. Previous studies have shown that triheme cytochrome PpcA from has bifunctional behavior toward substance analogue. It reduce but protein AH2QDS. Using stopped-flow kinetic measurements we were able demonstrate other periplasmic members PpcA-family (PpcB, PpcD and PpcE) showed same behavior. extent electron is thermodynamically controlled favoring reduction cytochromes. NMR spectra recorded 13C,15N-enriched samples presence increasing amounts perturbations chemical shift signals on cytochromes backbone NH 1H heme methyl map their interaction regions with AQDS, showing each forms low-affinity binding complex through well-defined positive surface vicinity IV I (PpcE). Docking calculations performed using allowed modeling interactions between at molecular level. Overall, results obtained provided important structural-functional relationships rationalize microbial respiration