Submitted to: Biochemistry and Cell Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/2/2009
Publication Date: 5/29/2009
Publication URL: http://hdl.handle.net/10113/33756
Citation: Krol, M., Ivanov, A., Booij, I.S., Mattoo, A.K., Sane, P.V., Huner, N.P. 2009. Absence of the major light harvesting antenna proteins alters the redox properties of photosystem II reaction centres in the chlorine F2 mutant of barley. Biochemistry and Cell Biology. 87:557-566. Interpretive Summary: Photosynthesis enables conversion of solar energy into food and the process is catalyzed by various multi-protein-chlorophyll complexes housed in the chloroplast. The influence of individual protein components in the structure, function and stability of these complexes is not yet understood. Interestingly, each of the key protein components that form the reaction center of photosystem II (PS II) complex and the associated antenna proteins are transiently modified by phosphorylation. The availability of a barley mutant deficient in the major antenna protein of PS II has made it possible to address the role of this protein in the PSII photochemistry and protein phosphorylation. In a collaborative work between the scientists at the University of Western Ontario in Canada and the USDA-ARS, it is shown for the first time that the absence of the major PS II antenna protein results in modifying the properties of the PS II reaction centers. Further, it is shown that commercial antibodies previously employed for research on chloroplast protein phosphorylation may have led to erroneous conclusions and that validation by additional methods, for example, radiolabeling is necessary to obtain unambiguous data. These results are of significance to researchers studying plant biology and molecular biology.
Technical Abstract: Although the chlorina F2 mutant of barley specifically exhibits reduced levels of the major light harvesting polypeptides (Lhcb) associated with photosystem II, thermoluminescence measurements of photosystem reaction centre photochemistry revealed that S2/S3QB- charge recombinations were shifted to lower temperatures, while the characteristic peak of S2QA- charge recombinations was shifted to higher temperatures compared to WT barley. Thus, we show that the absence of the major light harvesting polypeptides affects the redox properties of photosystem II reaction centres. Radiolabeling studies in vivo and in vitro with [32P]-orthophosphate or [''32P]-ATP, respectively, demonstrated that the D1 photosystem II reaction centre polypeptide is phosphorylated in both the WT and the F2 mutant. In contrast to the radiolabelling results, phosphorylation of D1 and other PSII proteins, although detected in WT barley, was ambiguous in the F2 mutant when the phosphor-threonine antibody method of detection was used. Thus, caution must be exercised in the use of commercially available phosphor-threonine antibodies to estimate thylakoid polypeptide phosphorylation. Furthermore, in membrano, the D1 polypeptide of the F2 mutant was less susceptible to trypsin treatment than that of WT barley. The role of the light harvesting complex in modulating the structure and function of the D1 polypeptide of photosystem II reaction centers is discussed.