| الوصف: |
Extremophilic organisms inhabit all four corners of the world, and among them, we find psychrophiles. Psychrophiles, which translates to cold-loving, are organisms that excel at survival and reproduction in cold environments and have developed marvellous molecular adaptations to achieve this. A crucial adaptation is the evolution of the so-called cold-active enzymes, which are biocatalysts able to overcome the exponential dampening of the catalytic activity induced by a decrease in the temperature. In other words, cold-active enzymes are highly efficient in the cold; however, they often pay the price in terms of lower thermodynamic stability. The current energy crisis emphasizes the need for improved ways to reduce our energy consumption by, among other means, developing novel technologies requiring less heat input. Therefore, high catalytic rates at low temperatures make cold-active enzymes attractive biocatalysts for industrial applications, such as food preparation and conservation, textile processing, biofuel production, and pharmacological formulation. This dissertation uses computational, biophysical, and structural approaches to study the structure-function relationship of cold-active enzymes. We were interested in understanding what determines cold-activity on a molecular level and whether the aforementioned stability price can be overcome to develop potentially highly active and stable enzymes. To achieve this, the author has identified, expressed, and characterized several novel enzymes from genomes of psychrophilic bacteria uniquely capable of subzero growth yet also tolerant towards relatively high temperatures. These studies have led to exciting observations showing that low thermodynamic stability is common amongst cold-active enzymes and that electrostatic interactions may play a crucial role in stability improvement. Furthermore, the author also chose to study an industrially relevant lactose-degrading enzyme previously discovered by our collaborators. We found that this enzyme is highly active but has a severely low tolerance against heat and chemical denaturation. Moreover, we were able to show how the stability and cold-activity of this enzyme are connected to its biological assembly, which is a rarely reported aspect of cold-active enzymes. |
