Functional role of Lys residues of Psb31 in electrostatic interactions with diatom photosystem II

Abstract

We recently revealed that positively charged amino acids of Psb31, an extrinsic subunit found in diatom photosystem II (PSII), are involved in electrostatic interactions with PSII intrinsic subunits. However, the molecular interactions of Psb31 with PSII remain unclear. Here, we report the functional contribution of Lys residues in the binding of Psb31 to PSII using site-directed mutants of Psb31. Each of the K33A, K39A, K54A, K56A, K57A, and K69A mutants exhibits decreased binding affinities to PSII concomitantly with decreases in the O evolution activity. Conversely, each of the K24A, K76A, K80A, and K117A mutants functionally binds to PSII in a manner similar to wild-type Psb31. These results provide evidence that some Lys residues of Psb31 are responsible for electrostatic interactions with PSII.

Structural basis for different types of hetero-tetrameric light-harvesting complexes in a diatom PSII-FCPII supercomplex

“…In addition, the fifth extrinsic subunit, Psb31 12 – 15 , is not found in the present structure, although it is present in one of the PSII-FCPII structures reported previously 8 . The binding site of Psb31 in the previously reported structure 8 is consistent with suggestions from our biochemical studies, including cross-linking, release-reconstitution, chemical modifications, and site-directed mutagenesis 13 , 16 – 18 .…”