A Mutant Small Heat Shock Protein with Increased Thylakoid Association Provides an Elevated Resistance Against UV-B Damage in Synechocystis 6803

Abstract

Besides acting as molecular chaperones, the amphitropic small heat shock proteins (sHsps) are suggested to play an additional role in membrane quality control. We investigated sHsp membrane function in the model cyanobacterium Synechocystis sp. PPC 6803 using mutants of the single sHsp from this organism, Hsp17. We examined mutants in the N-terminal arm, L9P and Q16R, for altered interaction with thylakoid and lipid membranes and examined the effects of these mutations on thylakoid functions. These mutants are unusual in that they retain their oligomeric state and chaperone activity in vitro but fail to confer thermotolerance in vivo. We found that both mutant proteins had dramatically altered membrane/lipid interaction properties. Whereas L9P showed strongly reduced binding to thylakoid and model membranes, Q16R was almost exclusively membrane-associated, properties that may be the cause of reduced heat tolerance of cells carrying these mutations. Among the lipid classes tested, Q16R displayed the highest interaction with negatively charged SQDG. In Q16R cells a specific alteration of the thylakoid-embedded Photosystem II (PSII) complex was observed. Namely, the binding of plastoquinone and quinone analogue acceptors to the Q B site was modified. In addition, the presence of Q16R dramatically reduced UV-B damage of PSII activity because of enhanced PSII repair. We suggest these effects occur at least partly because of increased interaction of Q16R with SQDG in the PSII complex. Our findings further support the model that membrane association is a functional property of sHsps and suggest sHsps as a possible biotechnological tool to enhance UV protection of photosynthetic organisms.

Alcohol stress, membranes, and chaperones

“…We recently provided evidence of the cholesterol-controlled lipid raft interaction of the mammalian Hspb11 (Hsp16.6; Török et al 2012). Overall, these data suggest that the membraneassociated pool(s) of Hsps may play a pivotal role in membrane protection under very varied stress conditions (Nakamoto and Vígh 2007;Balogi et al 2008;Horváth et al 2008;Horváth and Vígh 2010;Horváth et al 2012).…”

“…After a heat shock, most of the newly synthesized Hsp17 in Synechocystis PCC 6803 was found to be associated with the thylakoid membranes (Horváth et al 1998;Glatz et al 1999), binding especially to certain "heat shock lipids" (Balogi et al 2005). A noteworthy finding was that an increased level of thylakoid association of Hsp17 provided improved resistance to UV-B damage in Synechocystis (Balogi et al 2008). The level of membrane association of Lo18 depends on the temperature upshift in Oenococcus oeni (Delmas et al 2001).…”

Adaptation of the Wine Bacterium Oenococcus oeni to Ethanol Stress: Role of the Small Heat Shock Protein Lo18 in Membrane Integrity

“…These sHsp have a molecular mass ranging from 12 to 43 kDa and can form large oligomers with molecular chaperone activity that protects polypeptides from aggregation (16)(17)(18)(19). The association of sHsp with lipid substrates is linked to conformational changes (20)(21)(22). The affinity of sHsp for lipids is sensitive to phospholipid type.…”

Small Heat Shock Protein Hsp17.8 Functions as an AKR2A Cofactor in the Targeting of Chloroplast Outer Membrane Proteins in Arabidopsis

“…The identification of in vivo substrates is crucial to understanding the physiological roles of sHsps (Basha et al, 2004). In addition to acting as molecular chaperones for unfolded proteins, sHsps have been reported to interact with lipids and to function in membrane quality control (Coucheney et al, 2005;Chowdary et al, 2007;Nakamoto and Vígh, 2007;Balogi et al, 2008). These findings expand the physiological roles of sHsps.…”