Abstract
Phycobilisomes, the light-harvesting supramolecular complex, are rapidly degraded during nitrogen deprivation and constructed after readdition of nitrogen. These processes have not yet been elucidated at the molecular level. Last year we reported that the molecular chaperone HtpG (Hsp90) interacted with linker polypeptides which are thought to be involved in stabilization of the phycobilisome assembly. Therefore, we hypothesized that HtpG is involved in phycobilisome degradation and reconstruction. In this study, the hypothesis was tested using htpG mutants of Synechococcus sp. PCC 7942. Both degradation and reconstruction of phycobilisomes in response to nitrogen availability were slowed down in the mutants, suggesting that HtpG could play a role in these processes. TEM analyses of negatively stained, nitrogen-starved phycobilisomes provided evidence that phycobilisome degradation was highly retarded in the mutants. These data suggest that HtpG is involved in the degradation/assembly of phycobilisomes by interacting with linker polypeptides directly.
