Thermoprotection by glycine betaine and choline.
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 degrees 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.
Caldas
Teresa
T
Biochimie génétique, Institut Jacques Monod, Université Paris 7, 2 place Jussieu, 75251 Paris Cedex 05, France1.
Demont-Caulet
Nathalie
N
Biochimie génétique, Institut Jacques Monod, Université Paris 7, 2 place Jussieu, 75251 Paris Cedex 05, France1.
Ghazi
Alexandre
A
Laboratoire des Biomembranes, ERS571/CNRS, Université Paris Sud, bat. 430, 91405 Orsay, France2.
Richarme
Gilbert
G
Biochimie génétique, Institut Jacques Monod, Université Paris 7, 2 place Jussieu, 75251 Paris Cedex 05, France1.
D001622:Betaine / Q000378:metabolism / Q000494:pharmacology*; D002794:Choline / Q000378:metabolism / Q000494:pharmacology*; D002950:Citrate (si)-Synthase / Q000737:chemistry / Q000378:metabolism; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D029968:Escherichia coli Proteins; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D018869:Heat-Shock Response; D009154:Mutation; D017510:Protein Folding; D001616:beta-Galactosidase / Q000378:metabolism
D029968:Escherichia coli Proteins; D018840:HSP70 Heat-Shock Proteins; D001622:Betaine; D002950:Citrate (si)-Synthase; D001616:beta-Galactosidase; C063842:dnaK protein, E coli; D002794:Choline