Abstract
Psychrophiles are extremophilic organisms capable of thriving in cold environments. Proteins from these cold-adapted organisms can remain physiologically functional at low temperatures, but are structurally unstable even at moderate temperatures. Here, we report the crystal structure of adenylate kinase (AK) from the Antarctic fish Notothenia coriiceps, and identify the structural basis of cold adaptation by comparison with homologues from tropical fishes including Danio rerio. The structure of N. coriiceps AK (AKNc) revealed suboptimal hydrophobic packing around three Val residues in its central CORE domain, which are replaced with Ile residues in D. rerio AK (AKDr). The Val-to-Ile mutations that improve hydrophobic CORE packing in AKNc increased stability at high temperatures but decreased activity at low temperatures, suggesting that the suboptimal hydrophobic CORE packing is important for cold adaptation. Such linkage between stability and activity was also observed in AKDr. Ile-to-Val mutations that destabilized the tropical AK resulted in increased activity at low temperatures. Our results provide the structural basis of cold adaptation of a psychrophilic enzyme from a multicellular, eukaryotic organism, and highlight the similarities and differences in the structural adjustment of vertebrate and bacterial psychrophilic AKs during cold adaptation.
Highlights
Extremophiles are organisms that can thrive in extreme environmental conditions of various physical and chemical parameters such as temperature, pressure, pH, and salinity[1,2,3]
11 residues differ between AKNc and the other two tropical adenylate kinase (AK), and six of them are found in the N- and C-terminal regions
The source organism of AKNc is the Antarctic fish N. coriiceps; the enzyme originated from a multicellular, eukaryotic psychrophile, whereas most previously characterized psychrophilic proteins were from psychrophilic microorganisms[4,5]
Summary
Extremophiles are organisms that can thrive in extreme environmental conditions of various physical and chemical parameters such as temperature, pressure, pH, and salinity[1,2,3]. To evaluate the molecular basis for the temperature adaptation of psychrophilic and thermophilic proteins, numerous comparative studies have performed comparisons with their mesophilic homologues[13,14,15,16,17,18]. Psychrophilic proteins tend to exhibit fewer intramolecular interactions than their mesophilic homologues, which, at low temperatures, would become too inflexible to perform the dynamic movements required for their biological functions[8,11,16,17,18,21,22]. We reported the crystal structures, thermal denaturation midpoints (Tm’s), temperature-activity profiles, and molecular dynamics trajectories of homologous adenylate kinases (AKs) from psychrophilic, mesophilic, and thermophilic bacteria[23,24,25,26]. AK1 is the most abundant cytosolic AK isozyme, exists in a monomeric state, and contains a short LID domain[33,34]
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