SWEET蛋白家族研究进展

SWEET是新发现的一类具有7次跨膜?-螺旋的糖运输蛋白,它们由2个重复的具有3次跨膜?-螺旋的MtN3 motif和一个起连接作用的跨膜?-螺旋组成.SWEET广泛存在于真核单细胞生物、高等植物以及动物中.它们在生殖发育、植物与微生物的相互作用、植物的逆境反应及衰老等许多方面起重要作用.最近的研究显示,原核生物中存在与真核生物SWEET类似的、只含有一个3次跨膜?-螺旋的蛋白,这些蛋白属于MtN3或PQ-Loop家族.从慢生根瘤菌中克隆的SWEET同源蛋白BjSemiSWEET1和已经鉴定的部分真核生物SWEET蛋白一样具有运输蔗糖的能力,这个结果与其他相关研究一起暗示真核生物7次跨膜?-螺旋的糖或氨基酸运输蛋白可能由原核生物中3次跨膜?-螺旋的小分子蛋白通过复制或横向基因转移融合进化而来,并且它们在行使功能时可能形成和其他许多膜转运蛋白相似的、具有12次跨膜结构的功能单位.对SWEET的研究将为揭示多种生命现象提供重要线索.

Research Advances of the SWEET Proteins Family

SWEET is a new group of sugar transporters characterized with seven transmembrane helices; they are composed of two 3-transmembrane-helix MtN3 motif tandemly connected by a link transmembrane helix. SWEETs deploy widely in various eukaryotes including unicellular organisms, animals and plants. They play important roles in reproduction and development of organisms in addition to interactions between plants and microbes, plant stress response and ageing, etc. Recently, research showed that prokaryotes contain 3-transmembrane-helix homologs of SWEET protein They belong either to the MtN3 family or the PQ-loop family. Among them, the SemiSWEET1 cloned from Bradyrhizobium showed sucrose transport activity similar to its eukaryotic homologous SWEETs. This result, together with other related research, suggests that eukaryotic 7-transmembrane-helix transporters may be evolved from their prokaryotic 3-transmembrane-helix homologs by gene duplication or horizontal gene transfer and fusion. In addition, they might form 12-transmembrane-helix structures like many other membrane transporters in fulfilling their functions. Investigation of SWEET will bring new insight into understanding of various biological phenomena.