Binding and functional properties of two new extrinsic components, cytochrome c-550 and a 12-kDa protein, in cyanobacterial photosystem II

Abstract

Cytochrome c-550, a low-potential c-type cytochrome, and a 12-kDa protein were recently shown to be associated extrinsically and stoichiometrically with purified photosystem II (PSII) complex of the thermophilic cyanobacterium Synechococcus vulcanus [Shen, J.-R., Ikeuchi, M., & Inoue, Y. (1992) FEBS Lett. 301, 145-149]. The binding and functional properties of these two extrinsic components in PSII were studied by means of release-reconstitution and thermoluminescence techniques. The following results were obtained: (i) cyt c-550 rebound appreciably to cyanobacterial PSII in the absence of the 33- and 12-kDa extrinsic proteins, but the presence of these two proteins facilitated the rebinding, affording a full level of binding equal to that in native PSII. (ii) The 12-kDa protein did not rebind to PSII at all unless the 33-kDa protein or cyt c-550 was present. It rebound only partially in the presence of either of these two proteins, but it rebound maximally when reconstituted together with both of them. (iii) Reconstitution with cyt c-550 or the 12-kDa protein alone in the absence of the 33-kDa protein did not restore the O2-evolving activity of CaCl2-washed PSII. Reconstitution with cyt c-550 in combination with the 33-kDa protein appreciably enhanced the activity, but the activity restoration was much more marked and reached a level close to that of the original activity when all three extrinsic proteins were included.(ABSTRACT TRUNCATED AT 250 WORDS)

Crystal structure of oxygen-evolving photosystem II fromThermosynechococcus vulcanusat 3.7-Å resolution

“…The newly assigned 12-kDa protein has an all-␣ architecture composed of five or more short ␣-helices, with no homologous structure in the database. This protein is located between the 33-kDa protein and cyt c550 but apart from the luminal surface of the membrane by Ϸ30 Å, in agreement with previous results that this protein has no direct contact with the membrane and cannot bind to PSII in the absence of the 33-kDa protein and cyt c550 (11). The arrangement of the three extrinsic proteins suggests that the 12-kDa protein helps to link the 33-kDa protein and cyt c550.…”

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

“…In any event, it is an interesting subject to be elucidated as to why the activity of PSII reconstituted with PsbO was largely stimulated by Cl Ϫ and Ca 2ϩ ions but that of PSII reconstituted with Psb31 was not. In PSII reconstituted with PsbO, rebinding of PsbV or PsbV and PsbU largely activated the oxygen evolution in the absence of Ca 2ϩ ion, or both Cl Ϫ and Ca 2ϩ ions, respectively (Table 6), which is similar to that reported in the cyanobacterial and red algal PSIIs (1,2,5,12). These have been interpreted to indicate that PsbV and PsbU function to optimize the availability of Cl Ϫ and Ca 2ϩ cofactors for water oxidation, with PsbV mainly functioning to optimize the availability of Ca 2ϩ and PsbU mainly functioning to optimize Cl Ϫ , respectively.…”

“…This level of restoration is considerably lower than those observed with PSIIs from other organisms. For example, upon reconstitution of all of the extrinsic proteins under normal conditions, restoration of the oxygen evolution has been reported to be 42% in spinach PSII (12), 42% in green algal PSII (7), 40% in Euglena PSII (6), 59 -74% in red algal PSII (5,12), and 79 -87% in PSII from a thermophilic cyanobacterium (1,12). This may be due in part to the harsh treatment of 4 M urea plus 0.2 M NaCl required to release all of the extrinsic proteins from the diatom PSII, which may have damaged the Mn 4 Ca cluster to some extent.…”

Mechanisms of Acido-Tolerance and Characteristics of Photosystems in an Acidophilic and Thermophilic Red Alga, Cyanidium Caldarium

“…At the lumenal side, there are three hydrophilic, peripheral subunits that function to maintain the oxygen-evolving activity. In the case of cyanobacteria, these three extrinsic proteins are the 33 kDa protein (PsbO), cytochrome c 550 (PsbV), and 12 kDa protein (PsbU) (Shen and Inoue, 1993). These proteins were also found in C. caldarium PSII (Enami et al, 1998) (see below).…”

“…This 20 kDa protein has been shown to be required for effective binding of the other two proteins, PsbV and PsbU, in the red algal PSII (Enami et al, 1998). In contrast, PsbV (cytochrome c 550 ) of cyanobacterial PSII is able to bind and function independent of other extrinsic proteins (Shen and Inoue 1993;Shen et al, 1995). Interestingly, PsbQ' from C. caldarium has a low homology with PsbQ (17 kDa protein) from green algae .…”