Mak. Jansen et al., ENGAGEMENT OF SPECIFIC SITES IN THE PLASTOQUINONE NICHE REGULATES DEGRADATION OF THE D1 PROTEIN IN PHOTOSYSTEM-II, The Journal of biological chemistry, 268(28), 1993, pp. 21246-21252
Rapid degradation of the photosystem-II reaction center protein, D1, i
s driven by visible and ultraviolet irradiance at low photon-flux in t
he intact plant. We find that all inhibitors of electron flow that rep
lace bound plastoquinone (Q(B)) from its niche on D1 inhibit UV-B-driv
en D1 degradation, but only some inhibit visible light-driven degradat
ion. Stabilization of the D1 protein by nitrophenol type inhibitors in
visible light depends on the dimensions of the side chain at position
6 of the phenyl ring. Likewise, resistance to trypsinization of D1 at
Arg-238 and to electron flow inhibitors in D1 mutant V219I (but not A
251V, F255Y, S264A, or L275F) are functions of position 6 side chain d
imensions in isolated thylakoids. We conclude that the configuration o
f the Q(B) niche controls D1 protein degradation in intact plants unde
r physiological photon flux. This is true irrespective of the spectral
quality of radiation driving degradation. We show that UV-B-driven D1
protein degradation, but not that driven by visible light, requires p
lastoquinone in the Q(B) niche to proceed. D1 degradation in visible l
ight occurs as long as specific regions at the end of helix D and in t
he D-de loop of the protein are not engaged. These regions, through su
bstrate (i.e. Q(B))-mediated stabilization, are proposed to regulate r
apid degradation of the D1 protein.