Psychrophilic enzymes: molecular basis of cold adaptation

Abstract

Abstract. Psychrophilic organisms have successfully provides enhanced abilities to undergo conformational colonized polar and alpine regions and are able to grow changes during catalysis. Thermal instability of coldefficiently at sub-zero temperatures. At the enzymatic adapted enzymes is therefore regarded as a consequence level, such organisms have to cope with the reduction of of their conformational flexibility. A survey of the psychrophilic enzymes studied so far reveals only minor chemical reaction rates induced by low temperatures in alterations of the primary structure when compared to order to maintain adequate metabolic fluxes. Thermal compensation in cold-adapted enzymes is reached mesophilic or thermophilic homologues. However, all known structural factors and weak interactions inthrough improved turnover number and catalytic effivolved in protein stability are either reduced in number ciency. This optimization of the catalytic parameters can originate from a highly flexible structure which or modified in order to increase their flexibility.Key words. Psychrophiles; extremophiles; cold adaptation; microbial proteins; protein stability; weak interactions; Antarctic.Psychrophiles live at the lowest temperatures which allow the development of living organisms. These extremophilic organisms, either prokaryotic or eukaryotic, represent a major class of the living world if we consider the vast extent of permanently cold environments on Earth, such as polar and alpine regions or deep-sea waters. The successful colonization of such severe ecological niches by psychrophiles, their diversity and abundance are now well recognized. The lower temperature limit of life is commonly defined as the freezing point of cellular water. Although apparently simple by definition, this limit can drop significantly below 0°C, the freezing point of pure water. For instance, the freezing point of a typical marine teleost ranges between −0.5 and −0.9°C. Sodium chloride is responsible for about 85% of the freezing point depression, and the remaining 15% is due to other small solutes. Synthesis of antifreeze glycoproteins and peptides can further depress the freezing point of body fluids or cellular water. These proteins lower the freezing point by a noncolligative mechanism without altering the melting point significantly, and are therefore also referred to as thermal hysteresis proteins [1,2]. They were first discovered in the blood sera of Antarctic fish living perennially at about −1.9°C, but have been now reported in many organisms including plants, insects, fungi and bacteria [3][4][5]. Levels of thermal hysteresis activity generally range from 0.1 to 0.3°C in bacteria, from 0.2 to 0.5°C in plants, from 0.7 to 1.5°C in fish and from 3 to 6°C in insects. Besides the synthesis of cryoprotectants which lead to freeze avoidance, several organisms have developed mechanisms of freeze tolerance, involving drastic metabolic modifica-* Corresponding author.

Structural, Kinetic, and Calorimetric Characterization of the Cold-active Phosphoglycerate Kinase from the AntarcticPseudomonas sp. TACII18

“…Life at low temperatures requires that psychrophilic organisms maintain sufficiently high metabolic fluxes despite thermal inhibition of enzyme reaction rates. In the case of intracellular enzymes, adaptation to cold can be achieved either by increasing k cat, or reducing K m , or both (39). This assumption is confirmed in the case of the psychrophilic PGK which adjusts both k cat and K m parameters, leading to a 2-fold improved catalytic efficiency with respect to the mesophilic PGK at 25°C.…”

“…3) from psychrophilic to thermophilic PGK strongly suggest their involvement in temperature adaptation by modulation of the external shell compactness. In addition, it is known that the extremities of a protein are preferential sites for denaturation (20,39). In T. maritima and B. stearothermophilus PGK the N and C termini are linked by two salt bridges (D2-K397 and K3-E387, T. maritima PGK numbering) whereas only one connects the extremities of the mesophilic enzymes (K5-E413 in yeast).…”

Comparative thermal unfolding study of psychrophilic and mesophilic subtilisin-like serine proteases by molecular dynamics simulations

“…It has been shown that when the medium temperature decreases from 37 to 0°C, the enzymatic reaction rates can be reduced by 30-to 80-fold (Lonhienne, Gerday, & Feller, 2000). In order to cope with the reduction in chemical reaction rates and further to maintain sufficient metabolic fluxes, enzymes produced by psychrophiles generally feature a higher catalytic efficiency (K cat /K m ) at low temperatures than their warm-active counterparts (Feller & Gerday, 1997). The main strategy adopted by the psychrophilic enzymes to adapt to cold environments is believed to be their high intrinsic structural flexibility (Feller & Gerday, 1997;Lonhienne et al, 2000;Zecchinon et al, 2001).…”

“…In order to cope with the reduction in chemical reaction rates and further to maintain sufficient metabolic fluxes, enzymes produced by psychrophiles generally feature a higher catalytic efficiency (K cat /K m ) at low temperatures than their warm-active counterparts (Feller & Gerday, 1997). The main strategy adopted by the psychrophilic enzymes to adapt to cold environments is believed to be their high intrinsic structural flexibility (Feller & Gerday, 1997;Lonhienne et al, 2000;Zecchinon et al, 2001). An increase in the structural flexibility can reduce the activation free energy which has to be overcome to reach the reaction intermediates, thus leading to a more efficient substrate turnover (Georlette et al, 2004).…”

Molecular Cloning and Chaperone Activity of DnaK from Cold-adapted Bacteria, KOPRI22215

“…Psychrophilic bacteria have been compared with mesophilic bacteria to provide clues for cold-adaptation. 1 The potential importance of molecular chaperones in efficient folding processes has been addressed for subzero temperatures.…”