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His/Met heme ligation in the PioA outer membrane cytochrome enabling light-driven extracellular electron transfer by Rhodopseudomonas palustris TIE-1

Li, Dao-Bo and Edwards, Marcus J and Blake, Anthony W and Newton-Payne, Simone E and Piper, Samuel EH and Jenner, Leon P and Sokol, Katarzyna P and Reisner, Erwin and Van Wonderen, Jessica H and Clarke, Thomas A and Butt, Julea N (2020) 'His/Met heme ligation in the PioA outer membrane cytochrome enabling light-driven extracellular electron transfer by Rhodopseudomonas palustris TIE-1.' Nanotechnology, 31 (35). ISSN 0957-4484

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Abstract

A growing number of bacterial species are known to move electrons across their cell envelopes. Naturally this occurs in support of energy conservation and carbon-fixation. For biotechnology it allows electron exchange between bacteria and electrodes in microbial fuel cells and during microbial electrosynthesis. In this context Rhodopseudomonas palustris TIE-1 is of much interest. These bacteria respond to light by taking electrons from their external environment, including electrodes, to drive CO2-fixation. The PioA cytochrome, that spans the bacterial outer membrane, is essential for this electron transfer and yet little is known about its structure and electron transfer properties. Here we reveal the ten c-type hemes of PioA are redox active across the window +250 to −400 mV versus Standard Hydrogen Electrode and that the hemes with most positive reduction potentials have His/Met and His/H2O ligation. These chemical and redox properties distinguish PioA from the more widely studied family of MtrA outer membrane decaheme cytochromes with ten His/His ligated hemes. We predict a structure for PioA in which the hemes form a chain spanning the longest dimension of the protein, from Heme 1 to Heme 10. Hemes 2, 3 and 7 are identified as those most likely to have His/Met and/or His/H2O ligation. Sequence analysis suggests His/Met ligation of Heme 2 and/or 7 is a defining feature of decaheme PioA homologs from over 30 different bacterial genera. His/Met ligation of Heme 3 appears to be less common and primarily associated with PioA homologs from purple non-sulphur bacteria belonging to the alphaproteobacteria class.

Item Type: Article
Divisions: Faculty of Science and Health > Life Sciences, School of
Depositing User: Elements
Date Deposited: 07 Oct 2020 15:15
Last Modified: 07 Oct 2020 15:15
URI: http://repository.essex.ac.uk/id/eprint/28835

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