Heterologous expression of a plant small heat-shock protein enhances Escherichia coli viability under heat and cold stress

A small heat-shock protein (sHSP) that shows molecular chaperone activity i n vitro was recently purified from mature chestnut (Castanea saliva) cotyle dons. This protein, renamed here as CsHSP17.5, belongs to cytosolic class I , as revealed by cDNA sequencing and immunoelectron microscopy. Recombinant CsHSP17.5 was overexpressed in Escherichia coli to study its possible func tion under stress conditions. Upon transfer from 37 degrees C to 50 degrees C, a temperature known to cause cell autolysis, those cells that accumulat ed CsHSP17.5 showed improved viability compared with control cultures. Sodi um dodecyl sulfate-polyacrylamide gel electrophoresis analysis of cell lysa tes suggested that such a protective effect in vivo is due to the ability o f recombinant sHSP to maintain soluble cytosolic proteins in their native c onformation, with little substrate specificity. To test the recent hypothes is that sHSPs may be involved in protection against cold stress, we also st udied the viability of recombinant cells at 4 degrees C. Unlike the major h eat-induced chaperone, GroEL/ES, the chestnut sHSP significantly enhanced c ell survivability at this temperature. CsHSP17.5 thus represents an example of a HSP capable of protecting cells against both thermal extremes. Consis tent with these findings, high-level induction of homologous transcripts wa s observed in vegetative tissues of chestnut plantlets exposed to either ty pe of thermal stress but not salt stress.