HtpG, the prokaryotic homologue of Hsp90, stabilizes a phycobilisome protein in the cyanobacterium Synechococcus elongatus PCC 7942

Abstract

SummaryHtpG, a homologue of HSP90, is essential for thermotolerance in cyanobacteria. It is not known how it plays this important role. We obtained evidence that HtpG interacts with linker polypeptides of phycobilisome in the cyanobacterium Synechococcus elongatus PCC 7942. In an htpG mutant, the 30 kDa rod linker polypeptide was reduced. In vitro studies with purified HtpG and phycobilisome showed that HtpG interacts with the linker polypeptide as well as other linker polypeptides to suppress their thermal aggregation with a stoichiometry of one linker polypeptide/HtpG dimer. We constructed various domain-truncated derivatives of HtpG to identify putative chaperone sites at which HtpG binds linker polypeptides. The middle domain and the N-terminal domain, although less efficiently, prevented the aggregation of denatured polypeptides, while the C-terminal domain did not. Truncation of the C-terminal domain that is involved in the dimerization of HtpG led to decrease in the anti-aggregation activity, while fusion of the N-terminal domain to the middle domain lowered the activity. In vitro studies with HtpG and the isolated 30 kDa rod linker polypeptide provided basically similar results to those with HtpG and phycobilisome. ADP inhibited the anti-aggregation activity, indicating that a compact ADP conformational state provides weaker aggregation protection compared with the others.

Light History Influences the Response of the Marine CyanobacteriumSynechococcussp. WH7803 to Oxidative Stress

“…These two major chaperone systems in bacteria are known to be activated in response to cold stress, high irradiance, and MV in Synechococcus sp. PCC 7942 Nakamoto, 2002, 2003;Sato et al, 2010). In contrast, clpP genes mostly responded to oxidative stress in HL cells, with three being activated (clpP2, clpP4, clpP3), while the clpP1 gene was repressed in both LL and HL cells ( Fig.…”

Physical Interaction between Bacterial Heat Shock Protein (Hsp) 90 and Hsp70 Chaperones Mediates Their Cooperative Action to Refold Denatured Proteins

“…Each PCR fragment was cloned into pT7Blue T-Vector (Novagen), digested with the respective restriction enzymes, and subcloned into pET-21a vector (Novagen) digested with the same enzymes. Construction of an overexpression vector for the C-terminally His-tagged HtpG has been described previously (18). The constructed plasmids were transformed into E. coli BL21 (DE3).…”

“…The importance of HtpG under low temperature and oxidative stresses in other bacteria, such as psychrophilic and pathogenic bacteria, has also been reported (15,16). Protein substrates for cyanobacterial and E. coli HtpG have been identified (17)(18)(19), but it is not known by what mechanism HtpG plays a role under stress at the molecular level. Recently, it was shown in vitro that the E. coli HtpG functions with the DnaK chaperone system to refold a denatured substrate.…”

Heat shock protein 90 from Escherichia coli collaborates with the DnaK chaperone system in client protein remodeling

“…However, the physiological implication of this association is unknown. In cyanobacteria, Hsp90 is important during stress conditions (6) and has been shown in an ATP-independent reaction to stabilize a linker polypeptide of phycobilisome, a large structure involved in photosynthesis (7).…”