2Lomonosov Moscow State University, Faculty of Biology, 119991 Moscow, Russia; fax: +7 (495) 939-4309; E-mail: email@example.com
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Received February 19, 2015; Revision received April 14, 2015
Hlip (high light-inducible proteins) are important for protection of the photosynthetic apparatus of cyanobacteria from light stress. However, the interaction of these proteins with chlorophyll–protein complexes of thylakoids remains unclear. The association of HliA/HliB stress proteins with photosystem 1 (PS1) complexes of the cyanobacterium Synechocystis PCC 6803 was studied to understand their function. Western blotting demonstrated that stress-induced HliA/HliB proteins are associated with PS1 trimers in wild-type cells grown under moderate light condition (40 µmol photons/m2 per sec). The content of these proteins increased 1.7-fold after light stress (150 µmol photons/m2 per sec) for 1 h. In the absence of PS1 trimers (ΔpsaL mutant), the HliA/HliB proteins are associated with PS1 monomers and the PS2 complex. HliA/HliB proteins are associated with PS1 monomers but not with PS1 trimers in Synechocystis PS2-deficient mutant grown at 5 µmol photons/m2 per sec; the content of Hli proteins associated with PS1 monomers increased 1.2-fold after light stress. The HliA/HliB proteins were not detected in wild-type cells of cyanobacteria grown in glucose-supplemented medium at 5 µmol photons/m2 per sec, but light stress induces the synthesis of stress proteins associated with PS1 trimers. Thus, for the first time, the association of HliA/HliB proteins not only with PS1 trimers, but also with PS1 monomers is shown, which suggests a universal role of these proteins in the protection of the photosynthetic apparatus from excess light.
KEY WORDS: high light-inducible proteins HliA/HliB, light stress, photosystem 1, cyanobacteria