Cytochrome ffrom the Antarctic psychrophile, Chlamydomonas raudensisUWO 241: structure, sequence, and complementation in the mesophile, Chlamydomonas reinhardtii

Although cytochrome ffrom the Antarctic psychrophile, Chlamydomonas raudensisUWO 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 petAfrom both Chlamydomonasspecies in either E. colior a C. reinhardtiiΔpetAmutant 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 fwas less stable upon heating than that of the mesophile. In contrast to C. raudensis, a C. reinhardtiiΔpetAmutant transformed with petAfrom C. raudensisexhibited the ability to undergo state transitions and a capacity for intersystem electron transport comparable to that of C. reinhardtiiwild type. However, the C. reinhardtiipetAtransformants accumulated lower levels of cytochrome b6/fcomplexes and exhibited lower light saturated rates of O2evolution than C. reinhardtiiwild type. We show that the presence of an altered form of cytochrome fin C. raudensisdoes 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 ffrom 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.Although cytochrome ffrom the Antarctic psychrophile, Chlamydomonas raudensisUWO 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 petAfrom both Chlamydomonasspecies in either E. colior a C. reinhardtiiΔpetAmutant 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 fwas less stable upon heating than that of the mesophile. In contrast to C. raudensis, a C. reinhardtiiΔpetAmutant transformed with petAfrom C. raudensisexhibited the ability to undergo state transitions and a capacity for intersystem electron transport comparable to that of C. reinhardtiiwild type. However, the C. reinhardtiipetAtransformants accumulated lower levels of cytochrome b6/fcomplexes and exhibited lower light saturated rates of O2evolution than C. reinhardtiiwild type. We show that the presence of an altered form of cytochrome fin C. raudensisdoes 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 ffrom 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.