PtsHSP19.6, a small heat-shock protein from the marine red alga Pyropia tenera (Rhodophyta), aggregates into granules and enhances heat tolerance

Abstract

The marine red alga Pyropia tenera (Rhodophyta) is one of the most valuable and widely cultivated Pyropia species. Temperature is a major factor that affects the growth and life cycle of Pyropia. Small heat-shock proteins (sHSPs) play a crucial role in heat stress response. Among sHSPs isolated from P. tenera, PtsHSP19.6 showed the strongest response to heat stress but not to other abiotic stresses such as desiccation and freezing. Although an α-crystallin domain was found in PtsHSP19.6, its amino acid sequence showed low homology with known sHSPs, except those from red algae. This led us to investigate whether PtsHSP19.6 from red algae has chaperone activity and is involved in high-temperature tolerance. PtsHSP19.6 significantly reduced the thermal aggregation of alcohol dehydrogenase used as a substrate. When PtsHSP19.6 was introduced into Escherichia coli, the transformed cells grew better than the control cells under high-temperature conditions. Fluorescence of the PtsHSP19.6-GFP fusion protein was detected from granules in the cytoplasm. The in vitro analysis data showed that PtsHSP19.6 forms oligomers with a molecular weight greater than 240？kDa in solution. This study showed that PtsHSP19.6 from P. tenera forms oligomers in solution and plays a role in heat tolerance, with a chaperone function similar to that observed in green plants.