@article {Dantas20151129,
	title = {Molecular interaction studies revealed the bifunctional behavior of triheme cytochrome PpcA from Geobacter sulfurreducens toward the redox active analog of humic substances},
	journal = {Biochimica et Biophysica Acta (BBA) - Bioenergetics},
	volume = {1847},
	number = {10},
	year = {2015},
	note = {n/a},
	pages = {1129 - 1138},
	abstract = {<p>Abstract Humic substances (HS) constitute a significant fraction of natural organic matter in terrestrial and aquatic environments and can act as terminal electron acceptors in anaerobic microbial respiration. Geobacter sulfurreducens has a remarkable respiratory versatility and can utilize the \{HS\} analog anthraquinone-2,6-disulfonate (AQDS) as a terminal electron acceptor or its reduced form (AH2QDS) as an electron donor. Previous studies set the triheme cytochrome PpcA as a key component for \{HS\} respiration in G. sulfurreducens, but the process is far from fully understood. In this work, \{NMR\} chemical shift perturbation measurements were used to map the interaction region between PpcA and AH2QDS, and to measure their binding affinity. The results showed that the \{AH2QDS\} binds reversibly to the more solvent exposed edge of PpcA heme IV. The \{NMR\} and visible spectroscopies coupled to redox measurements were used to determine the thermodynamic parameters of the PpcA:quinol complex. The higher reduction potential of heme {\.I}V\} (- 127 mV) compared to that of \{AH2QDS\} (- 184 mV) explains why the electron transfer is more favorable in the case of reduction of the cytochrome by the quinol. The clear evidence obtained for the formation of an electron transfer complex between \{AH2QDS\} and PpcA, combined with the fact that the protein also formed a redox complex with AQDS, revealed for the first time the bifunctional behavior of PpcA toward an analog of the HS. Such behavior might confer selective advantage to G. sulfurreducens, which can utilize the \{HS\} in any redox state available in the environment for its metabolic needs.</p>
},
	keywords = {Electron transfer},
	issn = {0005-2728},
	doi = {https://doi.org/10.1016/j.bbabio.2015.06.004},
	url = {http://www.sciencedirect.com/science/article/pii/S0005272815001139},
	author = {Joana M Dantas and Oleksandr Kokhan and P Raj Pokkuluri and Salgueiro, , Carlos A.}
}
