C. Funk et al., THE NUCLEAR-ENCODED CHLOROPHYLL-BINDING PHOTOSYSTEM-II-S PROTEIN IS STABLE IN THE ABSENCE OF PIGMENTS, The Journal of biological chemistry, 270(50), 1995, pp. 30141-30147
The 22-kDa chlorophyll a/b-binding protein (CAB) (psbS gene product) i
s associated with photosystem II and related to the CAB gene family. H
ere we report that the PSII-S protein unlike other chlorophyll-binding
proteins is stable in the absence of pigments. It is present in etiol
ated spinach plants and accumulates in the dark progressively with the
cellular development of the seedlings. Furthermore, it is present in
several pigment-deficient mutants. Analysis of the pigment composition
of the PSII-S protein isolated from etiolated plants suggests that ne
ither carotenoids nor chlorophyll precursors are involved in its stabi
lization in the dark, Exposure of etiolated spinach to light leads to
further accumulation of the PSII-S protein, which appears more early t
han other chlorophyll-binding proteins. Accumulation of the PSII-S pro
tein in green plants is developmentally regulated and restricted to ph
otosynthetic tissues. It is suggested that the function of the PSII-S
protein may not be light-harvesting but it could act as a ligand chape
rone required for transient binding of pigments during biogenesis or t
urnover of chlorophyll-binding proteins. Such function would be essent
ial for coordination between pigment biosynthesis and ligation as well
as avoiding toxic effects of non-bound chlorophyll molecules.