%0 Journal Article
%T Psychrophilic Enzymes: From Folding to Function and Biotechnology
%A Georges Feller
%J Scientifica
%D 2013
%I Hindawi Publishing Corporation
%R 10.1155/2013/512840
%X Psychrophiles thriving permanently at near-zero temperatures synthesize cold-active enzymes to sustain their cell cycle. Genome sequences, proteomic, and transcriptomic studies suggest various adaptive features to maintain adequate translation and proper protein folding under cold conditions. Most psychrophilic enzymes optimize a high activity at low temperature at the expense of substrate affinity, therefore reducing the free energy barrier of the transition state. Furthermore, a weak temperature dependence of activity ensures moderate reduction of the catalytic activity in the cold. In these naturally evolved enzymes, the optimization to low temperature activity is reached via destabilization of the structures bearing the active site or by destabilization of the whole molecule. This involves a reduction in the number and strength of all types of weak interactions or the disappearance of stability factors, resulting in improved dynamics of active site residues in the cold. These enzymes are already used in many biotechnological applications requiring high activity at mild temperatures or fast heat-inactivation rate. Several open questions in the field are also highlighted. 1. Introduction ¡°Coping with our cold planet¡± [1], the title of this recent review unambiguously stresses a frequently overlooked aspect: the Earth¡¯s biosphere is predominantly cold and permanently exposed to temperatures below 5¡ãC. Such low mean temperature mainly arises from the fact that 71% of the Earth¡¯s surface is covered by oceans that have a constant temperature of 2¨C4¡ãC below 1000£¿m depth, irrespective of the latitude. The polar regions account for another 15%, to which the glacier and alpine regions must be added as well as the permafrost representing more than 20% of terrestrial soils. Although inhospitable, all these low temperature biotopes have been successfully colonized by cold-adapted organisms (Figure 1). Psychrophiles thrive in permanently cold environments (in thermal equilibrium with the medium) and even at subzero temperatures in supercooled liquid water. Such extremely cold conditions are encountered, for instance, in salty cryopegs at £¿10¡ãC in the Arctic permafrost [2, 3], in the brine veins between polar sea ice crystals at £¿20¡ãC [4¨C6], or in supercooled cloud droplets [7, 8]. Unusual microbiotopes have also been described, such as porous rocks in Antarctic dry valleys hosting microbial communities surviving at £¿60¡ãC [9, 10]. Cryoconite holes on glacier surfaces represent another permanently cold biotope hosting complex microbial communities [11, 12]. These
%U http://www.hindawi.com/journals/scientifica/2013/512840/