The Antarctic Psychrophile Chlamydomonas sp. UWO 241 Preferentially Phosphorylates a Photosystem I-Cytochrome b₆/f Supercomplex

Abstract

Chlamydomonas sp. UWO 241 (UWO 241) is a psychrophilic green alga isolated from Antarctica. A unique characteristic of this algal strain is its inability to undergo state transitions coupled with the absence of photosystem II (PSII) light-harvesting complex protein phosphorylation. We show that UWO 241 preferentially phosphorylates specific polypeptides associated with an approximately 1,000-kD pigment-protein supercomplex that contains components of both photosystem I (PSI) and the cytochrome b 6 /f (Cyt b 6 /f) complex. Liquid chromatography nano-tandem mass spectrometry was used to identify three major phosphorylated proteins associated with this PSI-Cyt b 6 /f supercomplex, two 17-kD PSII subunit P-like proteins and a 70-kD ATP-dependent zinc metalloprotease, FtsH. The PSII subunit P-like protein sequence exhibited 70.6% similarity to the authentic PSII subunit P protein associated with the oxygen-evolving complex of PSII in Chlamydomonas reinhardtii. Tyrosine-146 was identified as a unique phosphorylation site on the UWO 241 PSII subunit P-like polypeptide. Assessment of PSI cyclic electron transport by in vivo P700 photooxidation and the dark relaxation kinetics of P700 + indicated that UWO 241 exhibited PSI cyclic electron transport rates that were 3 times faster and more sensitive to antimycin A than the mesophile control, Chlamydomonas raudensis SAG 49.72. The stability of the PSI-Cyt b 6 /f supercomplex was dependent upon the phosphorylation status of the PsbP-like protein and the zinc metalloprotease FtsH as well as the presence of high salt. We suggest that adaptation of UWO 241 to its unique low-temperature and high-salt environment favors the phosphorylation of a PSI-Cyt b 6 /f supercomplex to regulate PSI cyclic electron transport rather than the regulation of state transitions through the phosphorylation of PSII light-harvesting complex proteins.

FtsH facilitates proper biosynthesis of photosystem I in Arabidopsis thaliana

“…The FtsH proteins play a crucial role in the proteolysis of membrane-embedded proteins, including the photodamaged PSII reaction center protein D1 (Lindahl et al, 2000;Bailey et al, 2002;Sakamoto et al, 2003). Likewise, thylakoid-bound FtsH proteases have been shown to participate in the quality control of the Cyt b 6 f complex (Ostersetzer and Adam, 1997;Malnoë et al, 2014) and possibly in the regulation of the PSI CET (Terashima et al, 2012;Szyszka-Mroz et al, 2015). Here, we demonstrate that FtsH2 and FtsH5 also play an important role in the biosynthesis of the PSI complex.…”

Characterization of photosynthetic ferredoxin from the Antarctic alga Chlamydomonas sp. UWO241 reveals novel features of cold adaptation

“…Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), immunoblotting and isoelectric focusing Protein samples were solubilized with 2% (w/v) SDS and 1% (v/v) b-mercaptoethanol and loaded on either an equal protein basis (soluble fraction and purified Fd) or an equal Chl basis (total fraction). Electrophoresis and protein transfer were performed as previously described (Szyszka-Mroz et al, 2015). Membranes were probed with primary antibody specific for Fd from C. reinhardtii (1 : 1000; Agrisera, V€ ann€ as, Sweden), and a horseradish peroxidase secondary antibody (Sigma; 1 : 10 000).…”

The labile interactions of cyclic electron flow effector proteins

“…Here, we will tie in with the protocol by Takahashi et al (18), which we used previously to assign heavy, Chl-containing SDG fractions as CEF supercomplexes. Our protocol was developed, like other variants (22,28,32), to build on the original findings by Iwai et al (21), which we will return to in the next section as an attempt to improve the poor Cyt-b 6 f retention in heavy SDG fractions in our hands.…”