二甲基亚砜丙酸内盐（DMSOP）是最近发现的一种新型海洋有机硫，储量巨大。研究表明，有些海洋微生物能够裂解DMSOP。但参与裂解DMSOP的微生物种类、酶和分子机制尚未被阐明。我们的科学假设是：DMSOP和DMSP的结构相似，广泛分布且代谢DMSP的SAR11细菌类群，可能参与DMSOP的代谢和循环，菌体内的DMSP裂解酶DddK可能具有裂解DMSOP的新功能。前期培养实验初步验证了该科学假设。本项目首先检测SAR11细菌HTCC1062以DMSOP为唯一硫源的生长特性，检测DMSOP对dddK基因的诱导表达作用，明确DddK在体内发挥功能。然后，异源表达DddK，从生化层面揭示DddK具有裂解DMSOP的新催化功能。最后，解析DddK-DMSOP等复合物的晶体结构，揭示DddK裂解DMSOP的分子机制。该研究将首次揭示海洋细菌代谢DMSOP的机制，为阐明有机硫生物循环过程提供重要依据。

Dimethylsulfoxonium propionate (DMSOP) is a kind of novel organic sulfur found recently, and massive amounts of DMSOP are stored in the ocean. Studies have shown that some microorganisms can metabolize DMSOP. However, the microbial species, enzymes, and molecular mechanisms involved in DMSOP cleavage are unclear. Because DMSOP has a similar structure with DMSP, our scientific hypothesis is that SAR11 bacteria, which is widely spread in the ocean and is the DMSP utilizing bacteria, may be involved in the metabolism and circulation of DMSOP. In addition, DMSP lyase DddK from SAR11 bacteria may be a functional DMSOP lyase. This scientific hypothesis has been preliminarily verified by the previous culture experiments. In this project, we will characterize the growth of SAR11 bacteria HTCC1062 with DMSOP as the only sulfur source and carry out transcriptional analysis of dddK. Therefore, the in vivo function of DddK will be confirmed. Subsequently, DddK will be expressed and purified. The new DMSOP cleavage function of DddK will be confirmed at biochemical level. Finally, the crystal structures of DddK-DMSOP and other complexes will be solved, and the molecular mechanism of DddK cleaving DMSOP will be illustrated. This project will provide a foremost insight into the mechanism of DMSOP metabolism by marine bacteria, which would lead to a better understanding of the organic sulfur biological cycle.