Kinetic characterization of His-tagged CP47 photosystem II in Synechocystis sp. PCC6803

Recently, construction of strains of Synechocystis sp. PCC6803 having a His(6) extension (His-tag) of the carboxyl terminus of the CP47 protein has been reported (T.M. Bricker et al, Biochim. Biophys. Acta 1409 (1998) 50; M.J. Reifler et al., in: Garab, Pusztai (Eds.) Proc. XIth International Congress on Photosynthesis, 1998). While these initial reports suggest a minimal impact of the His-tag upon Photosystem (PS) II function, a more thorough analysis of the kinetic properties of the modified complex is essential. This communication reports on a more detailed kinetic analysis to assess possible perturbations of PS II due to the genetic addition of the His-tag on the CP47 protein. It was found that: (1) Patterns of flash O(2) yield exhibited normal period four oscillations and the associated fits of the Kok-Joliot S-state cycling parameters were virtually identical to the wild type; (2) O(2) release kinetics during the S(3)-S(0) transition were experimentally indistinguishable from the wild type; (3) S-state decay measurements indicate slightly faster decays of the S(2) and S(3) states compared to the wild type; (4) fluorescence measurements indicate that the kinetics of the forward reaction of electron transfer from Q(A)(-) to Q(B) and back-reactions of Q(A)(-) with PS II electron donors are similar in the His-tag and wild-type strains. It is therefore concluded that the addition of the His-tag results in a minimal perturbation of PS II function.