Proteases are associated with a minor fucoxanthin chlorophyll a/c-binding protein from the diatom,Chaetoceros gracilis |
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Authors: | Ryo Nagao Tatsuya Tomo Eri Noguchi Takehiro Suzuki Akinori Okumura Rei Narikawa Isao Enami Masahiko Ikeuchi |
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Affiliation: | 1. Department of Life Sciences (Biology), Graduate School of Art and Sciences, University of Tokyo, Komaba 3-8-1, Meguro-ku, Tokyo, 153-8902, Japan;2. Department of Biology, Faculty of Science, Tokyo University of Science, Kagurazaka 1-3, Shinjuku-ku, Tokyo, 162-8601, Japan;3. PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan;4. Biomolecular Characterization Team, RIKEN Advanced Science Institute, Hirosawa 2-1, Wako, Saitama 351-0198, Japan;5. Department of Integrated Sciences in Physics and Biology, College of Humanities and Sciences, Nihon University, 3-25-40 Sakurajosui, Setagaya-ku, Tokyo 156-8550, Japan |
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Abstract: | We previously showed that most subunits in the oxygen-evolving photosystem II (PSII) preparation from the diatom Chaetoceros gracilis are proteolytically unstable. Here, we focused on identifying the proteases that cleave PSII subunits in thylakoid membranes. Major PSII subunits and fucoxanthin chlorophyll (Chl) a/c‐binding proteins (FCPs) were specifically degraded in thylakoid membranes. The PSI subunits, PsaA and PsaB, were slowly degraded, and cytochrome f was barely degraded. Using zymography, proteolytic activities for three metalloproteases (116, 83, and 75 kDa) and one serine protease (156 kDa) were detected in thylakoid membranes. Two FCP fractions (FCP-A and FCP-B/C) and a photosystem fraction were separated by sucrose gradient centrifugation using dodecyl maltoside‐solubilized thylakoids. The FCP-A fraction featured enriched Chl c compared with the bulk of FCP-B/C. Zymography revealed that 116, 83, and 94 kDa metalloproteases were mostly in the FCP-A fraction along with the 156 kDa serine protease. When solubilized thylakoids were separated with clear-native PAGE, zymography detected only the 83 kDa metalloprotease in the FCP-A band. Because FCP-A is selectively associated with PSII, these FCP-A-associated metalloproteases and serine protease may be responsible for the proteolytic degradation of FCPs and PSII in thylakoid membranes. |
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