Binding and Functional Properties of Five Extrinsic Proteins in Oxygen-evolving Photosystem II from a Marine Centric Diatom, Chaetoceros gracilis*

Abstract

Oxygen-evolving photosystem II (PSII) isolated from a marine centric diatom, Chaetoceros gracilis, contains a novel extrinsic protein (Psb31) in addition to four red algal type extrinsic proteins of PsbO, PsbQ , PsbV, and PsbU. In this study, the five extrinsic proteins were purified from alkaline Tris extracts of the diatom PSII by anion and cation exchange chromatographic columns at different pH values. Reconstitution experiments in various combinations with the purified extrinsic proteins showed that PsbO, PsbQ , and Psb31 rebound directly to PSII in the absence of other extrinsic proteins, indicating that these extrinsic proteins have their own binding sites in PSII intrinsic proteins. On the other hand, PsbV and PsbU scarcely rebound to PSII alone, and their effective bindings required the presence of all of the other extrinsic proteins. Interestingly, PSII reconstituted with Psb31 alone considerably restored the oxygen evolving activity in the absence of PsbO, indicating that Psb31 serves as a substitute in part for PsbO in supporting oxygen evolution. A significant difference found between PSIIs reconstituted with Psb31 and with PsbO is that the oxygen evolving activity of the former is scarcely stimulated by Cl ؊ and Ca 2؉ ions but that of the latter is largely stimulated by these ions, although rebinding of PsbV and PsbU activated oxygen evolution in the absence of Cl ؊ and Ca 2؉ ions in both the former and latter PSIIs. Based on these results, we proposed a model for the association of the five extrinsic proteins with intrinsic proteins in diatom PSII and compared it with those in PSIIs from the other organisms.

Cross-linking Evidence for Multiple Interactions of the PsbP and PsbQ Proteins in a Higher Plant Photosystem II Supercomplex

“…In cyanobacteria, there are also homologs of PsbP and PsbQ, termed CyanoP and CyanoQ, respectively (7,8), but these have not yet been included in current structural models. Red algae and diatoms have their own specific lumenally bound extrinsic subunits, such as PsbQЈ and Psb31 (9,10). Interestingly, the PsbP and PsbQ proteins in green plants seem to have evolved from CyanoP and CyanoQ in cyanobacteria, although considerable genetic and functional modifications have occurred to generate the forms of these proteins seen in eukaryotes today (11).…”

Novel Features of Eukaryotic Photosystem II Revealed by Its Crystal Structure Analysis from a Red Alga

“…The other two subunits, PsbU and PsbV, are present in PSII of cyanobacteria and most eukaryotic algae including red algae, diatom etc (11,(13)(14)(15), whereas they are replaced by two nonhomologous subunits, PsbQ (17 kDa) and PsbP (23 kDa), in the green lineage including green algae and higher plants (11,(15)(16)(17)(18)(19)(20). Proteins homologous to PsbQ and PsbP were also found in cyanobacteria (cyanoPsbQ and cyano-PsbP) (15)(16)(17)(18)(19)(20)(21), as well as some eukaryotic algae such as diatom (14). The cyanoQ and cyanoP, however, have been lost in the purified cyanobacterial PSII, and no crystal structure of PSII from eukaryotic organisms has been solved; therefore, the association pattern of these proteins with PSII is not clear.…”

Release of the Oxygen‐Evolving Complex Subunits from Photosystem II Membranes in Phosphorylation Condition under Light Stress

“…This may be because PsbP and PsbQ proteins do not directly, but do bind to PSII complex only by PsbO that binds to the PSII core complex. 31 So the release of PsbP and PsbQ proteins is not or less influenced by ROS generated in the PSII core complex and may be initiated just by absorption of visible light. Actually, previous study showed that PsbP and PsbQ proteins released more easily than PsbO protein did under high light condition.…”