Cytochrome f from the Antarctic psychrophile, Chlamydomonas raudensis UWO 241: structure, sequence, and complementation in the mesophile, Chlamydomonas reinhardtii |
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Authors: | Loreta Gudynaite-Savitch Michael Gretes Rachael M Morgan-Kiss Leonid V Savitch John Simmonds Susanne E Kohalmi Norman P A Hüner |
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Institution: | (1) Department of Biology and The Biotron, University of Western Ontario, London, Canada, N6A 5B7;(2) Department of Microbiology, University of Illinois, Champagne-Urbana, 61801, USA;(3) ECORC, Agriculture and Agri-Food Canada, Ottawa, Canada, K1A 0C6;(4) Present address: Department of Biology, Plant Molecular Biology, University of Ottawa, Ottawa, Canada, K1N 6N5;(5) Present address: Department of Botany, University of British Columbia, Vancouver, Canada |
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Abstract: | Although cytochrome f from the Antarctic psychrophile, Chlamydomonas raudensis UWO 241, exhibits a lower apparent molecular mass (34 kD) than that of the mesophile C. reinhardtii (41 kD) based on SDS-PAGE, both proteins are comparable in calculated molecular mass and show 79% identity in amino acid
sequence. The difference in apparent molecular mass was maintained after expression of petA from both Chlamydomonas species in either E. coli or a C. reinhardtii ΔpetA mutant and after substitution of a unique third cysteine-292 to phenylalanine in the psychrophilic cytochrome f. Moreover, the heme of the psychrophilic form of cytochrome f was less stable upon heating than that of the mesophile. In contrast to C. raudensis, a C. reinhardtii ΔpetA mutant transformed with petA from C. raudensis exhibited the ability to undergo state transitions and a capacity for intersystem electron transport comparable to that of
C. reinhardtii wild type. However, the C. reinhardtii
petA transformants accumulated lower levels of cytochrome b
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/f complexes and exhibited lower light saturated rates of O2 evolution than C. reinhardtii wild type. We show that the presence of an altered form of cytochrome f in C. raudensis does not account for its inability to undergo state transitions or its impaired capacity for intersystem electron transport
as previously suggested. A combined survey of the apparent molecular mass, thermal stability and amino acid sequences of cytochrome
f from a broad range of mesophilic species shows unequivocally that the observed differences in cytochrome f structure are
not related to psychrophilly. Thus, caution must be exercised in relating differences in amino acid sequence and thermal stability
to adaptation to cold environments.
Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users. |
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Keywords: | Chlamydomonas raudensis Chlamydomonas reinhardtii Cytochrome f Thermostability State transitions Electron transport |
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