含OsmC（Osmotically inducible protein C）结构域和α/β水解酶结构域的双结构域蛋白存在于多个海洋细菌的基因组序列中，但是，关于这类酶的催化特性及其生理作用目前还不清楚。Est22是北极表层海水细菌产生的一个含潜在过氧化酶OsmC结构域和Abhydrolase_5水解酶结构域的新型酯酶。本项目拟以Est22为例研究含OsmC的双结构域酶蛋白的催化特性及其生理作用。首先研究Est22的酯酶活性、过氧化酶活性及OsmC结构域对其酯酶活性的影响，揭示Est22的催化特性。其次，通过结构分析、突变和生化分析，阐明Est22降解酯类和/或过氧化物底物的分子机制及其两个结构域间相互作用的结构基础。最后，通过RT-qPCR分析、蛋白质印迹分析、基因敲除和回补实验，揭示Est22在菌株适应极地海洋环境中所起的生理作用。研究结果将为阐明极地海洋细菌的环境适应机制提供重要依据。

Two-domain proteins with an osmotically inducible protein C (OsmC) domain and a α/β hydrolase domain are present in many genome sequences of marine bacteria. However, the catalytic properties and physiological role of these two-domain proteins is still unknown. Est22 is a novel two-domain esterase from marine bacterium isolated from arctic surface water, containing an OsmC domain and an Abhydrolase_5 family hydrolase domain. This project intends to study Est22 to illustrate the catalytic properties, catalytic mechanism and physiological role of two-domain proteins containing an OsmC domain. The esterase activity and peroxidase activity of Est22 will be biochemically characterized, and the impact of OsmC domain on the esterase activity of Est22 will also be studied. Structural analysis in combination with mutational and biochemical analysis will reveal the catalytic mechanism of Est22 against esters and/or peroxides and the structural basis for domain-domain interaction. Transcriptional and western analysis under different conditions will tell the expression pattern of Est22, and gene knockout and complementation experiments will show the role of Est22 in environmental adaption of marine bacteria. Our results in this project will provide important basis for illustrating the mechanism for adaption of marine bacteria to polar extreme environments.