The isolation, purification, and properties of a putative small heat shock protein (sHsp), named SsHSP14.1, from the hyperthermophilic archaeon Sulfolobus solfataricus have been investigated. The sHsp was successfully expressed and purified from Escherichia coli. In vivo chaperone function of SsHSP14.1 for preventing aggregation of proteins during heating was investigated. It was found that recombinant SsHSP14.1 with a molecular mass of 17.8 kDa prevented E. coli proteins from aggregating in vivo at 50 degrees C. This result suggested that SsHSP14.1 confers a survival advantage on mesophilic bacteria by preventing protein aggregation at supraoptimal temperatures. In vitro, the purified SsHSP14.1 protein was able to prevent Candida antarctica lipase B from aggregation for up to 60 min at 80 degrees C. Moreover, the SsHSP14.1 enhanced thermostability of bromelain extending its half-life at 55 degrees C by 67%.
The small heat shock protein SsHSP14.1 from the hyper-thermophilic archeaon, Sulfolobus solfataricus (S. solfataricus) was able to protect proteins from thermal aggregation and prevent enzymes from heat induced inactivation. According to the 3D (dimensional) structural model of SsHSP14.1 developed by us before, the region L5-7 (β5-β7, 68-82 residues) plays an important role for the oligomerization of SsHSP14.1 and its chaperone function. Here, to validate the findings, an in-depth investigation was conducted of both the wild type SsHSP14.1 and its deletion mutant DEL75-79. With E. coli proteins and bromelain as substrate, the deletion mutant DEL75-79 can protect them from thermo-aggregating as effective as the wild protein. Interestingly, unlike the wild protein, DEL75-79 was unable to prevent bromelain and EcoRI from thermo-inactivating. Results of size exclusion HPLC showed that the oligomerization state was changed in mutant protein. This was in accordance with the changed structure and lower hydrophobicity of DEL75-79. These outcomes proved that the L5-7 loop did play a role for the oligomerizing SsHSP14.1, and that the residues 75-79 were indispensable for its function of prevent enzymes from thermo-inactivating.
SsHSP14.1, a novel sHSP from the hyper-thermophilic archaeon Sulfolobus solfataricus (S. solfataricus), is reported herein to function to protect EcoR I from heat-induced inactivation. A predicted salt bridge and hydrophobic interactions were found to be important for this function.
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