title: Energetics of protein stability at extreme environmental temperatures in bacterial trigger factors.
abstract: Trigger factor is the first molecular chaperone interacting cotranslationally with virtually all nascent polypeptides synthesized by the ribosome in bacteria. The stability of this primary folding assistant was investigated using trigger factors from the Antarctic psychrophile Pseudoalteromonas haloplanktis, the mesophile Escherichia coli, and the hyperthermophile Thermotoga maritima. This series covers nearly all temperatures encountered by living organisms. We show that proteins adapt their stability over the whole range of biological temperatures via adjustments of the same fundamental mechanisms, involving increases in enthalpic stabilization and decreases in unfolding rates, in parallel with the environmental temperature. Enthalpic stabilization in trigger factors is characterized by large increases in the melting temperature, T(m), ranging from 33 to 96.6 °C, associated with similarly large increases in unfolding enthalpy as revealed by differential scanning calorimetry. Stopped-flow spectroscopy shows that the folding rate constants for the three investigated proteins are similar, whereas the unfolding rate constants differ by several orders of magnitude, revealing that kinetic resistance to unfolding drives adjustments of protein stability. While the unusual stability of hyperthermophilic proteins has attracted much attention, this study indicates that they are an extreme case of a more general continuum, the other extreme being represented by natively unstable proteins from psychrophiles.
authors.affiliation: Laboratory of Biochemistry, Center for Protein Engineering, University of Liège, B-4000 Liège-Sart Tilman, Belgium.
authors.forename: Caroline
authors.initials: C
authors.lastname: Struvay
authors.forename: Sonia
authors.initials: S
authors.lastname: Negro
authors.forename: André
authors.initials: A
authors.lastname: Matagne
authors.forename: Georges
authors.initials: G
authors.lastname: Feller
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D002151:Calorimetry; D002152:Calorimetry, Differential Scanning; D003001:Cloning, Molecular; D004734:Energy Metabolism; D004926:Escherichia coli / Q000378:metabolism*; D007700:Kinetics; D011489:Protein Denaturation; D017510:Protein Folding; D031161:Pseudoalteromonas / Q000378:metabolism*; D020124:Thermotoga maritima / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins