title: Evidence for interaction between the triheme cytochrome PpcA from Geobacter sulfurreducens and anthrahydroquinone-2,6-disulfonate, an analog of the redox active components of humic substances.
abstract: The bacterium Geobacter sulfurreducens displays an extraordinary respiratory versatility underpinning the diversity of electron donors and acceptors that can be used to sustain anaerobic growth. Remarkably, G. sulfurreducens can also use as electron donors the reduced forms of some acceptors, such as the humic substance analog anthraquinone-2,6-disulfonate (AQDS), a feature that confers environmentally competitive advantages to the organism. Using UV-visible and stopped-flow kinetic measurements we demonstrate that there is electron exchange between the triheme cytochrome PpcA from Gs and AQDS. 2D-(1)H-(15)N HSQC NMR spectra were recorded for (15)N-enriched PpcA samples, in the absence and presence of AQDS. Chemical shift perturbation measurements, at increasing concentration of AQDS, were used to probe the interaction region and to measure the binding affinity of the PpcA-AQDS complex. The perturbations on the NMR signals corresponding to the PpcA backbone NH and heme substituents showed that the region around heme IV interacts with AQDS through the formation of a complex with a definite life time in the NMR time scale. The comparison of the NMR data obtained for PpcA in the presence and absence of AQDS showed that the interaction is reversible. Overall, this study provides for the first time a clear illustration of the formation of an electron transfer complex between AQDS and a G. sulfurreducens triheme cytochrome, shedding light on the electron transfer pathways underlying the microbial oxidation of humics.
authors: Requimte-CQFB, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus Caparica, 2829-516 Caparica, Portugal.
authors: Joana M
authors: JM
authors: Dantas
authors: Requimte-CQFB, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus Caparica, 2829-516 Caparica, Portugal.
authors: Leonor
authors: L
authors: Morgado
authors: Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. da República, 2780-157 Oeiras, Portugal; Departamento de Química, Faculdade de Ciências e Tecnologia, FCT, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal.
authors: Teresa
authors: T
authors: Catarino
authors: Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, IL 60439 USA.
authors: Oleksandr
authors: O
authors: Kokhan
authors: Biosciences Division, Argonne National Laboratory, Argonne, IL 60439 USA.
authors: P Raj
authors: PR
authors: Pokkuluri
authors: Requimte-CQFB, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus Caparica, 2829-516 Caparica, Portugal. Electronic address: csalgueiro@fct.unl.pt.
authors: Carlos A
authors: CA
authors: Salgueiro
mesh_terms: D000880:Anthraquinones / Q000378:metabolism*; D003580:Cytochromes / Q000378:metabolism*; D045302:Geobacter / Q000201:enzymology*; D006812:Humic Substances; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010084:Oxidation-Reduction; D013056:Spectrophotometry, Ultraviolet
chemical_list: D000880:Anthraquinones; D003580:Cytochromes; D006812:Humic Substances; C000589127:anthrahydroquinone-2,6-disulfonate; C408124:anthraquinone-2,6-disulfonate
keywords: AQDS; Electron transfer; Geobacter; Humics; Multiheme cytochromes; NMR