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。