Mutagenesis of Ser24 of cytochrome b559 α subunit affects PSII activities in Chlamydomonas reinhardtii

In order to study the functions of cytochrome b(559) (Cyt b(559)) in photosystem two (PSII) activity, mutant S24F of Chlamydomonas reinhardtii was constructed using site directed mutagenesis, in which Serine (24) (Ser(24)) locating downstream of Histidine(23) (His(23)) in a subunit of Cyt b(559) was replaced by Phenylalanine (Phe). Physiological and biochemical analysis showed that mutant S24F could be grown photoautotrophically or photoheterotrophically. However, their growth rate was slower either on HSM or TAP medium than that of the control; Analysis of PSII activity revealed that its oxygen evolution was about 71% of wild type (WT); The Photochemical efficiency of PSII (FvIFm) of S24F was reduced 0.23 compared with WT, S24F was more sensitive to strong light irradiance than the wild type; Furthermore, SDS-PAGE and Western-blotting analysis indicated that the expression levels of a subunit of Cyt b(559), LHCII and PsbO of S24F were a little less than those of the wild type. Overall, these data suggests that Ser24 plays a significant role in making Cyt b(559) structure maintain PSII complex activity of oxygen evolution although it is not directly bound to heme group.