Effects of phospholipase and lipase treatments on photosystem II core dimer from a thermophilic cyanobacterium.
Lipids are important components of transmembrane protein complexes. In order to study the roles of lipids in photosystem II (PSII), we treated the PSII core dimer complex from a thermophilic cyanobacterium Thermosynechococcus vulcanus with phospholipase A(2) (PLA(2)) and lipase, and examined their effects on PSII structure and function. PLA(2)-treatment decreased the content of phospholipid, phosphatidylglycerol (PG) by 59%, leading to a decrease of oxygen evolution by 40%. On the other hand, although treatment with lipase specifically decreased the content of monogalactosyldiacylglycerol (MGDG) by 52%, it decreased oxygen evolution only by 16%. This indicates that PG plays a more important role in PSII than MGDG. Both PLA(2)- and lipase-treatments induced neither the dissociation of PSII dimer, nor any loss of polypeptides. The degradation of PG resulted in a damage to the Q(B)-binding site as demonstrated from photoreduction activity of 2,6-dichlorophenolindophenol and chlorophyll fluorescence yields in the absence or presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea, and the dependencies of oxygen evolution on various electron acceptors before and after PLA(2)- or lipase-treatments. However, there were approximately three and five molecules of PG and MGDG per PSII reaction center left in the PSII dimeric complex after the PLA(2)- and lipase-treatments. These lipids are therefore bound to the interior of the protein matrix and resistant to the lipase treatments. The resistance of these lipids against PLA(2)- and lipase-treatments may be a specific feature of PSII from the thermophilic cyanobacterium, suggesting a possible correlation between binding of lipids and thermostability of PSII.
Leng
Jing
J
Graduate School of Natural Science and Technology, Department of Biology, Faculty of Science, Okayama University, Okayama 700-8530, Japan.
Sakurai
Isamu
I
Wada
Hajime
H
Shen
Jian-Ren
JR
D015086:2,6-Dichloroindophenol; D000458:Cyanobacteria / Q000737:chemistry / Q000378:metabolism*; D004579:Electron Transport; D008049:Lipase / Q000378:metabolism*; D008055:Lipids / Q000032:analysis; D010100:Oxygen / Q000378:metabolism; D010715:Phosphatidylglycerols / Q000378:metabolism*; D054467:Phospholipases A2 / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000378:metabolism*; D020836:Protein Structure, Quaternary
D008055:Lipids; D010715:Phosphatidylglycerols; D045332:Photosystem II Protein Complex; D015086:2,6-Dichloroindophenol; D008049:Lipase; D054467:Phospholipases A2; D010100:Oxygen