Collaborative Research: Biosynthesis of Dimethylsulforiopropionate and its Precursor in Relation to Sulfur Emission from Plants

高等植物和海藻中已知的两种主要的二甲基磺酸化合物是s -甲基蛋氨酸（SMM）和3-二甲基磺酰丙酸（DMSP）。SMM广泛分布于高等植物和藻类中，通常为中等水平；目前尚不清楚SMM是否有任何生理功能。DMSP只存在于某些高等植物和海藻中，但可以达到非常高的水平，特别是在高盐度和低氮条件下。DMSP是甜菜碱的硫类似物，和甜菜碱一样，具有渗透保护剂的作用。众所周知，SMM和DMSP都是二甲硫化物（DMS）气体的前体，而二甲硫化物是大气硫的主要生物来源。SMM可能是陆地DMS排放的主要前体，而DMSP则是海洋和沿海环境中DMS的主要前体。因此，这两种化合物都是生物硫排放的核心。尽管SMM和DMSP在自然硫循环中起着关键作用，但直到最近，人们对它们的生物合成知之甚少，只知道它们都是从蛋氨酸中提取的。本研究的总体目标是阐明海藻和高等植物中DMSP生物合成的步骤，了解产生和切割SMM的酶以及它们如何分离，并寻找将SMM转化为DMSP的酶。这些结果将为了解世界上最丰富的大气硫生物源的起源提供生物化学方面的见解。这是一个与密歇根州立大学盖奇博士实验室的合作项目。

The two major dimethylsulfonium compounds known in higher plants and marine algae are S-methylmethionine (SMM) and 3-dimethylsulfoniopropionate (DMSP). SMM is widely distributed in higher plants and algae, typically at moderate levels; it is not clear whether SMM has any physiological funtion. DMSP occurs only in certain higher plants and marine algae, but can reach very high levels, particularly in conditions of high salinity and low nitrogen. DMSP is a sulfur analog of a betaine and, like betaines, functions as an osmoprotectant. Both SMM and DMSP are known to be precursors of dimethylsulfide (DMS) gas, which is the predominant biological source of atmospheric sulfur. SMM is probably the principal precursor of terrestial DMS emissions, whereas DMSP is the main DMS preursor in the oceans and coastal environments. Both compounds are therefore central to biogenic sulfur emission. Despite the pivotal roles of SMM and DMSP in the natural sulfur cycle, until recently little was known about their biosynthesis except that both are derived from methionine. The overall aims of this research are to elucidate the steps in DMSP biosynthesis in marine algae as well as in higher plants, to understand the enzymes that produce and cleave SMM and how these are kept apart, and to seek the enzymes that convert SMM to DMSP. The results would provide biochemical insight into the origin of the world's most abundant biogenic sources of atmospheric sulfur. This is a collaborative project with Dr. Gage's laboratory at Michigan State University.