Peptide Induced Conformational Changes of E. Coli DegP (HtrA) Protease / 生物化学与生物物理进展

The DegP protein, functioning as both chaperone and protease, plays a critical role in degrading and removing denatured or damaged proteins in the cellular envelope during heat shock and other stresses. So far, several proteins have been identified as its natural targets. A carboxyle-terminal peptide derived from the PapG pilus, one of the in vivo substrates for DegP, has been shown to activate the protease. Nevertheless, neither the details nor the physiological implications of such activation have been studied. The evidence that DegP undergoes conformational changes upon binding the peptide derived from C-terminal sequence of pilus subunit PapG has been presented. It demonstrated that upon binding this peptide, detectable changes can be observed for both secondary and tertiary structures of DegP, as examined by CD spectroscopy. Gel filtration and dynamic light scattering analysis also revealed that the size of DegP becomes smaller to a minor extent. Moreover, both the hydrophobic surfaces and catalytic sites of DegP were found to expose slightly in the presence of the peptide. Upon peptide binding, a less flexible and more rigid conformation of DegP was obtained as analyzed by fluorescence anisotropy. The physiological implications of these observations for DegP are discussed.

HSP12.1, A Small Heat Shock Protein in C.elegans, Has Chaperone-like Activity / 生物化学与生物物理进展

Many kinds of small heat shock proteins (sHSPs) are able to prevent protein aggregation in stress, which show the ATP independent chaperone-like activity. The smallest protein HSP12.1 in sHSP family of the nematode Caenorhabditis elegans exhibits chaperone-like activities in vitro. It prevents protein aggregation in a certain extent when use insulin, ADH and lysozyme as the substrates, though it is not as efficient as the typical chaperones (such as HSP16.1 in C. elegans). By contrast, the other three sHSP12s (HSP12.2, HSP12.3 and HSP12.6), which have similar molecular masses and primary structure, appear devoid of in vitro chaperone-like activities. In addition, overexpressing HSP12.1 enhances cell thermotolerance of Escherichia coli. The survival rate of the HSP12.1 overexpressed cells is 4-fold higher than the control, yet whether it does the same function in C. elegans is still unknown. Results indicate that C-terminal region is not necessary for the chaperone-like activity of sHSPs, for HSP12.1 terminates a short C-terminal tail. N-terminal domain may play a relatively important role in the exhibition of chaperone-like activities, while ?-crystalline domain may also involve in this function.