Investigating the Chaperone Ability of Two sHsp Isoforms Based on Protection of a Model Substrate

Abstract

ZmHsp17.0‐CII and ZmHsp17.8‐CII are Class II small heat shock proteins (sHsps) found in maize (corn). These highly conserved sHsps protect client proteins from irreversible aggregation in times of stress. Each sHsp was expressed as a fusion protein with a chitin‐binding domain on the C‐terminus that allows for chitin affinity column purification. The increase in light scattering of the model substrate citrate synthase (CS) after heat shock at 43 °C in solution was measured using a fluorescence spectrophotometer to detect protein aggregation. By comparing the light scattering curves of CS alone with a solution containing CS plus varying amounts of ZmHsp17.0‐CII and ZmHsp17.8‐CII, a clear, consistent reduction in aggregation was seen for all molar ratios of sHsp monomer: CS monomer of 1:1 and greater, with greater reduction at higher concentrations. In addition, more efficient substrate protection was seen in ZmHsp17.8‐CII than in ZmHsp17.0‐CII, which could indicate different substrate specificity or different chaperone capability of the two proteins. These results demonstrate that ZmHsp17.0‐CII and ZmHsp17.8‐CII are concentration‐dependant molecular chaperones.This work was supported in part by a grant from The College of Wooster, and from the Howard Hughes Medical Institute through the Undergraduate Science Education Program.