Auxiliary functions of the PsbO, PsbP and PsbQ proteins of higher plant Photosystem II: A critical analysis

Numerous studies over the last 25 years have established that the extrinsic PsbO, PsbP and PsbQ proteins of Photosystem II play critically important roles in maintaining optimal manganese, calcium and chloride concentrations at the active site of Photosystem II. Chemical or genetic removal of these components induces multiple and profound defects in Photosystem II function and oxygen-evolving complex stability. Recently, a number of studies have indicated possible additional roles for these proteins within the photosystem. These include putative enzymatic activities, regulation of reaction center protein turnover, modulation of thylakoid membrane architecture, the mediation of PS II assembly/stability, and effects on the reducing side of the photosystem. In this review we will critically examine the findings which support these auxiliary functions and suggest additional lines of investigations which could clarify the nature of the functional interactions of these proteins with the photosystem.

Research highlights
► In this review we have examined proposed auxiliary functions for the PsbO, PsbP and PsbQ proteins of Photosystem II.
► The evidence supporting these proposed functions has been critically examined with respect to the existing literature.
► Where possible, experimental approaches has been suggested to clarify the roles played by these proteins within the photosystem.