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research article

Modulation of heme redox potential in the cytochrome c6 family

Worrall, Jonathan A R
•
Schlarb-Ridley, Beatrix G
•
Reda, Torsten
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2007
Journal of the American Chemical Society

Cytochrome c6A is a unique dithio-cytochrome of green algae and plants. It has a very similar core structure to that of bacterial and algal cytochromes c6 but is unable to fulfill the same function of transferring electrons from cytochrome f to photosystem I. A key feature is that its heme midpoint potential is more than 200 mV below that of cytochrome c6 despite having His and Met as axial heme-iron ligands. To identify the molecular origins of the difference in potential, the structure of cytochrome c6 from the cyanobacterium Phormidium laminosum has been determined by X-ray crystallography and compared with the known structure of cytochrome c6A. One salient difference of the heme pockets is that a highly conserved Gln (Q51) in cytochrome c6 is replaced by Val (V52) in c6A. Using protein film voltammetry, we found that swapping these residues raised the c6A potential by +109 mV and decreased that of c6 by almost the same extent, -100 mV. X-ray crystallography of the V52Q protein showed that the Gln residue adopts the same configuration relative to the heme as in cytochrome c6 and we propose that this stereochemistry destabilizes the oxidized form of the heme. Consequently, replacement of Gln by Val was probably a key step in the evolution of cytochrome c6A from cytochrome c6, inhibiting reduction by the cytochrome b6f complex and facilitating establishment of a new function.

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Type
research article
DOI
10.1021/ja072346g
Author(s)
Worrall, Jonathan A R
Schlarb-Ridley, Beatrix G
Reda, Torsten
Marcaida, Maria J
Moorlen, Robert J
Wastl, Juergen
Hirst, Judy
Bendall, Derek S
Luisi, Ben F
Howe, Christopher J
Date Issued

2007

Publisher

American Chemical Society

Published in
Journal of the American Chemical Society
Volume

129

Issue

30

Start page

9468

End page

75

Editorial or Peer reviewed

NON-REVIEWED

Written at

EPFL

EPFL units
IBI-SV  
Available on Infoscience
November 17, 2016
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/131171
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