Enhancement of Chaperone Activity of Plant-Specific Thioredoxin through γ-Ray Mediated Conformational Change

Abstract

AtTDX, a thioredoxin-like plant-specific protein present in Arabidospis is a thermo-stable and multi-functional enzyme. This enzyme is known to act as a thioredoxin and as a molecular chaperone depending upon its oligomeric status. The present study examines the effects of γ-irradiation on the structural and functional changes of AtTDX. Holdase chaperone activity of AtTDX was increased and reached a maximum at 10 kGy of γ-irradiation and declined subsequently in a dose-dependent manner, together with no effect on foldase chaperone activity. However, thioredoxin activity decreased gradually with increasing irradiation. Electrophoresis and size exclusion chromatography analysis showed that AtTDX had a tendency to form high molecular weight (HMW) complexes after γ-irradiation and γ-ray-induced HMW complexes were tightly associated with a holdase chaperone activity. The hydrophobicity of AtTDX increased with an increase in irradiation dose till 20 kGy and thereafter decreased further. Analysis of the secondary structures of AtTDX using far UV-circular dichroism spectra revealed that the irradiation remarkably increased the exposure of β-sheets and random coils with a dramatic decrease in α-helices and turn elements in a dose-dependent manner. The data of the present study suggest that γ-irradiation may be a useful tool for increasing holdase chaperone activity without adversely affecting foldase chaperone activity of thioredoxin-like proteins.

Direct Radiation Effects on the Structure and Stability of Collagen and Other Proteins

“…Irradiationo fasolution at room temperature leads to the formation of free radicals from the solvent( e.g.,h ydroxyl from water) as the main primary products.T hese speciest hen chemically react with proteins, leadingt os econdary processes, such as backbonec leavage and, in some cases, aggregation of the fragments formed; [11] crosslinking between proteins to form largers ystems; or even nanoparticles with diameters in the 10 nm range, [12] and generally quenching or enhancement of biological activity. [13] The effect on activity is thought to be due to ar adioinduced conformational change, in accordance with other reports that provide evidence for the unfoldingo fp roteins after irradiation. [14,15] All of these indirect effectsr equired iffusion of free radicals from the solvent to the protein, which occurs at rates that decrease by severalo rders of magnitude from room to cryogenic temperatures.…”

Chaperome heterogeneity and its implications for cancer study and treatment

“…The dynamic interactions between chaperones, co-chaperones, and clients governing normal cellular function, and the partial functional overlap among the component machineries of the chaperome, are both altered under stress (22). This has been seen in yeast (23,24), plants (25)(26)(27), and other organisms (28). For example, Hsp82, the yeast HSP90, forms stable complexes with most chaperones mainly after exposure to a stress condition such as the introduction of the exogenous mammalian proteins v-Src or the glucocorticoid receptor (23,29).…”

Adapting to stress — chaperome networks in cancer

“…This is modulated via its tetratricopeptide repeat (TPR) domains, as their deletion results in increased disulfide reductase activity and loss of the holdase function 168 . Formation of the oligomeric form is associated with a conformational change in AtTDX structure 169 .…”