Role of the PB-loop in ApcE and Phycobilisome Core Function in Cyanobacterium Synechocystis sp. PCC 6803статья
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Аннотация:The phycobilisome (PBS) is a giant highly-structured pigment-protein antennaof cyanobacteria and red algae. PBS is composed of the phycobiliproteinsand several linker polypeptides. The large core-membrane linker protein(LCM or ApcE) influences many features and functions of PBS and consistsof several domains including the chromophorylated PB-domain. Beinghomologous to the phycobiliprotein α-subunits this domain includes a so-calledPB-loop insertion whose functions are still unknown. We have createdthe photoautotrophic mutant strain of the cyanobacterium Synechocystis sp.PCC 6803 with lacking PB-loop. Using various spectral techniques we havedemonstrated that this mutation does not destroy the PBS integrity andthe internal PBS excitation energy transfer pathways. At the same time,the deletion of the PB-loop leads to the decrease of connectivity betweenthe PBS and thylakoid membrane and to the compensatory increase of therelative photosystem II content. Mutation provokes the violation of the thylakoid membranes arrangement, the inability to perform state transitions,and diminishing of the OCP-dependent non-photochemical PBS quenching.In essence, even such a minute mutation of the PBS polypeptide component,like the PB-loop deletion, becomes important for the concerted function ofthe photosynthetic apparatus.