Protein stability and enzyme activity at extreme biological temperatures

Abstract

Psychrophilic microorganisms thrive in permanently cold environments, even at subzero temperatures. To maintain metabolic rates compatible with sustained life, they have improved the dynamics of their protein structures, thereby enabling appropriate molecular motions required for biological activity at low temperatures. As a consequence of this structural flexibility, psychrophilic proteins are unstable and heat-labile. In the upper range of biological temperatures, thermophiles and hyperthermophiles grow at temperatures > 100 °C and synthesize ultra-stable proteins. However, thermophilic enzymes are nearly inactive at room temperature as a result of their compactness and rigidity. At the molecular level, both types of extremophilic proteins have adapted the same structural factors, but in opposite directions, to address either activity at low temperatures or stability in hot environments. A model based on folding funnels is proposed accounting for the stability-activity relationships in extremophilic proteins.

Stepwise Adaptations to Low Temperature as Revealed by Multiple Mutants of Psychrophilic α-Amylase from Antarctic Bacterium

“…In psychrophiles, this constraint is alleviated by the synthesis of cold-active enzymes to maintain metabolic fluxes compatible with life. The prevailing hypothesis assumes that cold-adapted enzymes have acquired a high catalytic activity at low temperature by improving their conformational flexibility at the expense of stability (7)(8)(9)(10). It has been shown that the crystal structure of psychrophilic enzymes is characterized by the disappearance of various noncovalent stabilizing interactions, resulting in both an improved dynamics of the enzyme conformation and in a weak stability (11)(12)(13)(14)(15)(16)(17).…”

Life in the Cold: Proteomics of the Antarctic Bacterium Pseudoalteromonas haloplanktis

“…From top to bottom, mass scale from ~150 to ~15 kDa. The intense red fluorescence of the trigger factor (TF) spot correlates with its upregulation at 4°C, whereas the intense green fluorescence of the DnaK spot correlates with its down-regulation Adapted with permission from Piette et al, 2010. © 2010 In a typical single 2D-gel (Fig.…”

“…Spot views on 2D-gels (circled) and three-dimensional images. Adapted with permission from Piette et al, 2010;Piette et al, 2011. © 2010Wiley and © 2011 American Society for Microbiology.…”

“…As a result of the strong conservation of primary and predicted secondary structures in P. haloplanktis TF, a model of its structure built by homology modeling is undistinguishable from the E. coli crystal structure. Reprinted with permission from Piette et al, 2010. © 2010 indicates that the psychrophilic TF is uniformly unstable and unfolds cooperatively.…”

“…It was shown that the high level of specific activity at low temperatures of coldadapted enzymes is a key adaptation to compensate for the exponential decrease in chemical reaction rates as the temperature is reduced. Such high biocatalytic activity arises from the disappearance of various non-covalent stabilizing interactions, resulting in an improved flexibility of the enzyme conformation Siddiqui & Cavicchioli, 2006;Feller, 2010). Whereas membrane structures are rigidified in cold conditions, an adequate fluidity is required to preserve the integrity of their physiological functions.…”