Probing the N-terminal sequence of spinach PsbO: evidence that essential threonine residues bind to different functional sites in eukaryotic photosystem II

Popelka, Hana; Yocum, Charles
June 2012
Photosynthesis Research;Jun2012, Vol. 112 Issue 2, p117
Academic Journal
The N-terminal E−L domain of the manganese-stabilizing protein (PsbO) from spinach prevents non-specific binding of the subunit to photosystem II (PSII) and deletions of the E−T or E−T sequences from the PsbO N-terminus reduce or impair, respectively, functional binding of PsbO to PSII (Popelkova et al., Biochemistry 42:6193-6200, ). The work presented here provides deeper insights into the interaction of PsbO with PSII. The data show that a single mutation, T → A in mature PsbO from spinach reduces the stoichiometry of its functional binding from two to one subunit per PSII and decreases reconstitution of activity to about 45 % of the wild-type control. Replacement of the E−L domain with M in the T15A PsbO mutant has no additional negative effect on recovery of O evolution activity, but it significantly weakens both functional and nonspecific binding of the truncated mutant to PSII. These results suggest that the T side-chain by itself is essential for binding of one of two PsbO subunits to eukaryotic PSII and that specific PSII-binding sites for PsbO are distinguishable; one PSII-binding site does not require PsbO-T and probably interacts with the other N-terminal domain of PsbO. Identity of the latter domain is revealed by a requirement for the presence of the E−L sequence that is shown here to be necessary for high-affinity binding of PsbO to PSII. When combined with previous results, the data presented here lead to a more detailed model for PsbO binding in eukaryotic PSII.


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