Analysis of photosynthetic complexes from a cyanobacterial ycf37 mutant
2006
Duhring, U. | Irrgang, K.D. | Lunser, K. | Kehr, J. | Wilde, A.
The Ycf37 protein has been suggested to be involved in the biogenesis and/or stability of the cyanobacterial photosystem I (PSI) [A. Wilde, K. Lunser, F. Ossenbuhl, J. Nickelsen, T. Borner, Characterization of the cyanobacterial ycf37: mutation decreases the photosystem I content, Biochem. J. 357 (2001) 211-216]. With Ycf37 specific antibodies, we analyzed the localization of Ycf37 within the thylakoid membranes of the cyanobacterium Synechocystis sp. PCC 6803. Inspection of a sucrose gradient profile indicated that small amounts of Ycf37 co-fractionated with monomeric photosynthetic complexes, but not with trimeric PSI. Isolating 3xFLAG epitope-tagged Ycf37 by affinity-tag purification rendered several PSI subunits that specifically co-precipitated with this protein. Blue-native PAGE newly revealed two monomeric PSI complexes (PSI and PSI*) in wild-type thylakoids. The lower amount of PsaK present in PSI* may explain its higher electrophoretic mobility. PSI* was more prominent in high-light grown cells and interestingly proved absent in the deltaycf37 mutant. PSI* appeared again when the mutant was complemented in trans with the wild-type ycf37 gene. In the deltaycf37 mutant the amount of trimeric PSI complexes was reduced to about 70% of the wild-type level with no significant changes in photochemical activity and subunit composition of the remaining photosystems. Our results indicate that Ycf37 plays a specific role in the preservation of PSI* and the biogenesis of PSI trimers.
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