Occupation of the QB-binding pocket by a photosystem II inhibitor triggers dark cleavage of the D1 protein subjected to brief preillumination.
The D1 protein of the photosystem (PS) II reaction center turns over very rapidly in a light-dependent manner initiated by its selective and specific cleavage. The cleavage of D1 was studied by using a PS II inhibitor, N-octyl-3-nitro-2,4,6-trihydroxybenzamide (PNO8), as a molecular probe. The following results were obtained. (i) D1 was selectively cleaved into 23-kDa N-terminal and 9-kDa C-terminal fragments in complete darkness by PNO8 at a single site in a D-E loop connecting membrane-spanning helices D and E. (ii) The cleavage was markedly enhanced when PS II was illuminated for a brief period before the addition of PNO8 in darkness. (iii) The effect of preillumination was slowly lost during incubation in the dark, with a decay half-time of approximately 1 h at 25 degrees C. (iv) The light intensity of preillumination required for the cleavage was much lower than that required for O2 evolution. (v) The light-triggered cleavage of D1 was observed in thylakoids, PS II membranes, and PS II core particles, but not in purified PS II reaction centers. More than 60% of D1 was cleaved into the two fragments with no other by-products. (vi) The cleavage reaction revealed a marked pH dependence that was considerably different from that for inhibition of PS II activity. The results are interpreted as indicating that the binding of PNO8 to the QB-binding pocket triggers proteolytic cleavage of D1 that has been previously modified during illumination.
Nakajima
Y
Y
Institute of Physical and Chemical Research (RIKEN), Wako, Saitama 351-01, Japan.
Yoshida
S
S
Inoue
Y
Y
Ono
T
T
D001549:Benzamides / Q000494:pharmacology; D001665:Binding Sites; D003624:Darkness; D005707:Gallic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism; D007700:Kinetics; D008027:Light; D015388:Organelles / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D010446:Peptide Fragments / Q000378:metabolism / Q000528:radiation effects; D045322:Photosynthetic Reaction Center Complex Proteins / Q000302:isolation & purification / Q000378:metabolism* / Q000528:radiation effects; D045332:Photosystem II Protein Complex; D018724:Spinacia oleracea / Q000378:metabolism*; D013997:Time Factors
D001549:Benzamides; D010446:Peptide Fragments; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; C100676:N-octyl-3-nitro-2,4,6-trihydroxybenzamide; D005707:Gallic Acid; D010100:Oxygen