title: Proteases are associated with a minor fucoxanthin chlorophyll a/c-binding protein from the diatom, Chaetoceros gracilis.
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 75kDa) and one serine protease (156kDa) 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 94kDa metalloproteases were mostly in the FCP-A fraction along with the 156kDa serine protease. When solubilized thylakoids were separated with clear-native PAGE, zymography detected only the 83kDa 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.
authors.affiliation: Department of Life Sciences (Biology), Graduate School of Art and Sciences, University of Tokyo, Komaba 3-8-1, Meguro-ku, Tokyo,153-8902, Japan. nagao.ryo@nihon-u.ac.jp
authors.forename: Ryo
authors.initials: R
authors.lastname: Nagao
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Tomo
authors.forename: Eri
authors.initials: E
authors.lastname: Noguchi
authors.forename: Takehiro
authors.initials: T
authors.lastname: Suzuki
authors.forename: Akinori
authors.initials: A
authors.lastname: Okumura
authors.forename: Rei
authors.initials: R
authors.lastname: Narikawa
authors.forename: Isao
authors.initials: I
authors.lastname: Enami
authors.forename: Masahiko
authors.initials: M
authors.lastname: Ikeuchi
mesh_terms: D015153:Blotting, Western; D061146:Chlorophyll Binding Proteins / Q000378:metabolism*; D017377:Diatoms / Q000378:metabolism*; D063347:Native Polyacrylamide Gel Electrophoresis; D010100:Oxygen / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D020524:Thylakoids / Q000378:metabolism*
chemical_list: D061146:Chlorophyll Binding Proteins; D045332:Photosystem II Protein Complex; D010447:Peptide Hydrolases; D010100:Oxygen