二甲基巯基丙酸内盐(dimethylsulfoniopropionate,DMSP)是全球重要的有机硫化合物之一,参与全球硫循环、信号传递及气候调节。全球DMSP的产量每年高达109 t。DMSP的主要生产者是海洋浮游植物及大型藻类,近年来发现一些海洋细菌也可以产生DMSP,是海洋中DMSP的一个重要来源。目前已报道的DMSP合成途径有3条:甲基化途径、转氨途径和脱羧途径,其中有5种DMSP合成关键酶被鉴定出来。根据近年来的研究成果,本文对DMSP合成过程中关键酶的研究进展进行综述,以期为进一步的研究提供思路。
Dimethylsulfoniopropionate (DMSP) is one of the most important organic sulfur compounds in the world. It participates in the global sulfur cycle, signal transmission and potential regulation of global climate. The production of DMSP can reach up to 109 tons every year, with the main producers being marine phytoplankton and macroalgae. In recent years, it has been reported that some marine bacteria can also produce DMSP, which is a previously overlooked source of DMSP. Up to date, three DMSP synthesis pathways have been identified: methylation pathway, transamination pathway and decarboxylation pathway. Five key enzymes involved in DMSP synthesis were identified. On the basis of the research results in recent years, this study reviewed the key enzymes involved in DMSP synthesis, and provided outlook for future research.
硫元素作为生物必需的大量元素之一,在地球上广泛存在,约占地壳成分的0.03%[
DMSP在海洋环境中广泛分布,其最早是在1948年从多管藻属的红藻中被鉴定出[
DMSP的生产者以甲硫氨酸为前体物质,通过甲基化反应、转氨反应和脱羧反应等催化过程在体内合成DMSP[
DMSP的3种生物合成途径
Three biosynthetic pathways of DMSP.
截至目前,已经报道的参与DMSP合成的关键酶有5种,包括DsyB[
DMSP是全球硫循环的重要参与者。DMSP不仅在海洋生物中发挥着重要的生理功能,其裂解产物DMS还可以通过参与云凝结核的形成对全球气候产生影响,因此,研究DMSP的合成机制具有重要的意义。目前已经有3条DMSP合成途径被报道,其中有5种DMSP合成关键酶被鉴定获得,但是尚无关于DMSP合成关键酶的晶体结构及催化机制的研究。本文对目前已报道的DMSP合成关键酶的研究进展进行系统阐述,梳理DMSP合成酶之间的联系与区别并进行讨论和展望,以期增进人们对DMSP产生过程及全球硫循环的理解。
第一个被鉴定的DMSP合成基因
Curson等的研究进一步发现,基因组中含有
海洋浮游植物和大型海藻等被认为是DMSP的重要生产者,不同种群细胞中的DMSP浓度差异较大[
虽然DSYB是DsyB的同源蛋白,系统发育分析表明DSYB来源于真核生物而DsyB来源于海洋α变形菌纲细菌,两者各自独立成支,这可能与微生物在进化中的基因复制与丢失有关[
硅藻在全球广泛分布,是海洋浮游植物中的一个重要类群,DMSP在一些海洋硅藻中可以积累到较高的胞内浓度[
重组表达的TpMMT催化反应的最适温度为25 ℃,最适酶活pH值为8.0,高浓度的氯化钠或氯化钾均会抑制TpMMT的酶活;TpMMT与DSYB/DsyB属于同功酶,但其与DSYB/DsyB的蛋白序列相似度很低[
除海水外,海洋沉积物中也有DMSP的积累。盐沼池塘、河口和深海的表层沉积物中的DMSP浓度(5−128 nmol/g)比沉积物上层水体中的DMSP浓度(0.01−0.70 nmol/mL)高出大约3个数量级[
重组表达的MmtN对SAM和甲硫氨酸的
The
重组表达的MmtN的底物特异性分析(修改自文献[
Substrate specificity analysis of recombinant MmtN (modified from reference [
在本研究选取的海水和沉积物样本中,含有
伯克霍尔德氏菌属(
目前已经报道的5种DMSP合成酶中(
DMSP合成关键酶
Key enzymes involved in the DMSP synthesis pathways
酶 |
来源 |
功能 |
分子质量 |
所属途径 |
主要分布 |
DsyB | 催化MTHB生成DMSHB的SAM依赖的甲基转移酶 |
~37.2 | 转氨途径 |
海水环境中的α变形菌纲细菌 |
|
DSYB | 催化MTHB生成DMSHB的SAM依赖的甲基转移酶 |
~40.0 | 转氨途径 |
海洋植物、珊瑚、部分硅藻及大多数甲藻 |
|
TpMMT | 催化MTHB生成DMSHB的SAM依赖的甲基转移酶 |
~36.4 | 转氨途径 |
部分硅藻 |
|
MmtN | 催化甲硫氨酸生成SMM的SAM依赖的甲基转移酶 |
~33.1 | 甲基化途径 |
海洋沉积物中的α变形菌纲细菌 |
|
BurB | 催化甲硫氨酸生成SMM的SAM依赖的甲基转移酶 |
~19.1 | 甲基化途径 |
伯克霍尔德菌属 |
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