A metabolic pathway for biosynthesis of the nonreducing disaccharide mannosylfructose (β-fructofuranosyl-α-mannopyranoside), an important osmolyte in
Agrobacterium tumefaciens
, was discovered. We have identified and functionally characterized two ORFs that correspond to genes (named
mfpsA
and
mfppA
) encoding the rare enzymes mannosylfructose-phosphate synthase and mannosylfructose-phosphate phosphatase, an associated phosphohydrolase. The
mfpsA
and
mfppA
genes are arranged in an operon structure, whose transcription is up-regulated by NaCl, resulting in the accumulation of mannosylfructose in the cells. Not only is the biosynthesis of mannosylfructose mechanistically similar to that of sucrose, but the corresponding genes for the biosynthesis of both disaccharides are also phylogenetic close relatives. Importantly, a protein phylogeny analysis indicated that mannosylfructose-phosphate synthase defines a unique group of mannosyltransferases.
发现了一种代谢途径,用于合成非还原二糖甘露果糖(β-果糖呋喃糖苷-α-甘露糖),这是农杆菌中重要的渗透保护物。我们已经确定并功能性地表征了两个ORF,它们对应于编码罕见酶甘露果糖磷酸合成酶和甘露果糖磷酸酶的基因(分别命名为mfpsA和mfppA),以及一个相关的磷酸酯酶。mfpsA和mfppA基因被排列成一个操作子结构,其转录受NaCl上调,导致细胞中甘露果糖的积累。甘露果糖的生物合成不仅在机理上类似于蔗糖,而且两种二糖的生物合成相应的基因也是系统发育上的近亲。重要的是,蛋白质系统发育分析表明,甘露果糖磷酸合成酶定义了一类独特的甘露糖转移酶。