Thermoprotection by glycine betaine and choline

Biochimie génétique, Institut Jacques Monod, Université Paris 7, 2 place Jussieu, 75251 Paris Cedex 05, France 1 Laboratoire des Biomembranes, ERS571/CNRS, Université Paris Sud, bat. 430, 91405 Orsay, France 2 Author for correspondence: Gilbert Richarme. Tel: +33 1 44 27 50 98. Fax: +33 1 44 27 35 80. e-mail: richarme{at}ccr.jussieu.fr Glycine betaine is mostly known as an osmoprotectant. It is involved in the osmotic adaptation of eukaryotic and bacterial cells, and accumulates up to 1 M inside cells subjected to an osmotic upshock. Since, like other osmolytes, it can act as a protein stabilizer, its thermoprotectant properties were investigated. In vitro , like protein chaperones such as DnaK, glycine betaine and choline protect citrate synthase against thermodenaturation, and stimulate its renaturation after urea denaturation. In vivo , the internal concentration of glycine betaine is neither increased nor decreased after heat shock (this contrasts with a massive increase after osmotic upshock). However, even in exponential-phase bacteria grown in usual minimal salts media, the internal glycine betaine concentration attains levels (around 50 mM) which can protect proteins against thermodenaturation in vitro . Furthermore, glycine betaine and choline restore the viability of a dnaK deletion mutant at 42 °C, suggesting that glycine betaine not only acts as a thermoprotectant in vitro , but also acts as a thermoprotectant for Escherichia coli cells in vivo . Keywords: glycine betaine, choline, osmoprotectant, thermoprotectant, heat-shock protein DnaK