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FEBS Lett. 2006 May 29;580(13):3029-34. Epub 2006 Apr 27.

Interaction of a small heat shock protein with light-harvesting cyanobacterial phycocyanins under stress conditions.

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Department of Biochemistry and Molecular Biology, Saitama University, 255 Shimo-Okubo, Saitama 338-8570, Japan.


Phycobiliproteins such as phycocyanins are the most abundant proteins found in cyanobacteria which are assembled to form the phycobilisome. Here, we showed that a small heat shock protein, HspA, interacts directly with phycocyanins from the cyanobacterium Synechococcus sp. strain PCC 7942 in vitro and suppresses inactivation of their light-harvesting functions due to heat denaturation in the presence of hydrogen peroxide. Under the denaturing conditions, phycobilisomes were de-assembled to lighter complexes and then aggregated. HspA associated with phycocyanins in the dissociated complexes, and suppressed the aggregation. The specific interaction between a small heat shock protein and phycocyanins was further supported by the fact that HspA and alpha-crystallin protected isolated phycocyanins from denaturation, while HtpG and lysozyme did not. The maximum protection was observed at a molar ratio of four HspA monomer per one phycocyanin (alpha beta) monomer.

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