Sulfoquinovosyl-diacylglycerol (SQDG) is one of the four lipids present in the thylakoid membranes. Depletion of SQDG causes different degrees of effects on photosynthetic growth and activities in different organisms. Four SQDG molecules bind to each monomer of photosystem II (PSII), but their role in PSII function has not been characterized in detail, and no PSII structure without SQDG has been reported. We analyzed the activities of PSII from an SQDG-deficient mutant of the cyanobacterium Thermosynechococcus elongatus by various spectroscopic methods, which showed that depletion of SQDG partially impaired the PSII activity by impairing secondary quinone (Q B ) exchange at the acceptor site. We further solved the crystal structure of the PSII dimer from the SQDG deletion mutant at 2.1 Å resolution and found that all of the four SQDG-binding sites were occupied by other lipids, most likely PG molecules. Replacement of SQDG at a site near the head of Q B provides a possible explanation for the Q B impairment. The replacement of two SQDGs located at the monomer-monomer interface by other lipids decreased the stability of the PSII dimer, resulting in an increase in the amount of PSII monomer in the mutant. The present results thus suggest that although SQDG binding in all of the PSII-binding sites is necessary to fully maintain the activity and stability of PSII, replacement of SQDG by other lipids can partially compensate for their functions.
Organizational Affiliation:
From the Research Institute for Interdisciplinary Science, Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530.
the Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, Tokyo 153-8902.
the Japan Science and Technology Agency, PRESTO, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, and.
the Division of Material Science, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan.
From the Research Institute for Interdisciplinary Science, Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, shen@cc.okayama-u.ac.jp.
BC [auth B] CF [auth E] CM [auth f] IF [auth F] NL [auth d]
BC [auth B], CF [auth E], CM [auth f], IF [auth F], NL [auth d], OL [auth d], PL [auth d], QE [auth D], RE [auth D], SE [auth D], WL [auth e], YI [auth b]
1,2-DIPALMITOYL-PHOSPHATIDYL-GLYCEROLE C38 H75 O10 P BIABMEZBCHDPBV-MPQUPPDSSA-N
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