The PsbP and PsbQ family proteins in the photosynthetic machinery of chloroplasts

• PsbP and PsbQ proteins are extrinsic subunits of the photosystem II in green plants.
• Many PsbP and PsbQ homologs exist in the thylakoid lumen of chloroplasts.
• Recent findings and new idea about PsbP and PsbQ family proteins are summarized.

The PsbP and PsbQ proteins are extrinsic subunits of the photosystem II in eukaryotic photosynthetic organisms including higher plants, green algae and euglena. It has been suggested that PsbP and PsbQ have evolved from their cyanobacterial homologs, while considerable genetic and functional modifications have occurred to generate the eukaryote-type proteins. In addition, number of PsbP and PsbQ homologs exist in the thylakoid lumen of chloroplasts. These homologs are nuclear-encoded and likely diverged by gene duplication, and recent studies have elucidated their various functions in the photosynthetic machinery. In this short review, recent findings and new idea about these components will be discussed.