Studies on the trehalose-phosphate synthase of Mycobacterium smegmatis: binding of heparin to the enzyme

Three enzymes for trehalose synthesis in Bradyrhizobium cultured bacteria and in bacteroids from soybean nodules

alpha,alpha-Trehalose is a disaccharide accumulated by many microorganisms, including rhizobia, and a common role for trehalose is protection of membrane and protein structure during periods of stress, such as desiccation. Cultured Bradyrhizobium japonicum and B. elkanii were found to have three enzymes for trehalose synthesis: trehalose synthase (TS), maltooligosyltrehalose synthase (MOTS), and trehalose-6-phosphate synthetase. The activity level of the latter enzyme was much higher than those of the other two in cultured bacteria, but the reverse was true in bacteroids from nodules. Although TS was the dominant enzyme in bacteroids, the source of maltose, the substrate for TS, is not clear; i.e., the maltose concentration in nodules was very low and no maltose was formed by bacteroid protein preparations from maltooligosaccharides. Because bacteroid protein preparations contained high trehalase activity, it was imperative to inhibit this enzyme in studies of TS and MOTS in bacteroids. Validamycin A, a commonly used trehalase inhibitor, was found to also inhibit TS and MOTS, and other trehalase inhibitors, such as trehazolin, must be used in studies of these enzymes in nodules. The results of a survey of five other species of rhizobia indicated that most species sampled had only one major mechanism for trehalose synthesis. The presence of three totally independent mechanisms for the synthesis of trehalose by Bradyrhizobium species suggests that this disaccharide is important in the function of this organism both in the free-living state and in symbiosis.

Three pathways for trehalose biosynthesis in mycobacteria

Trehalose is present as a free disaccharide in the cytoplasm of mycobacteria and as a component of cell-wall glycolipids implicated in tissue damage associated with mycobacterial infection. To obtain an overview of trehalose metabolism, we analysed data from the Mycobacterium tuberculosis genome project and identified ORFs with homology to genes encoding enzymes from three trehalose biosynthesis pathways previously characterized in other bacteria. Functional assays using mycobacterial extracts and recombinant enzymes derived from these ORFs demonstrated that mycobacteria can produce trehalose from glucose 6-phosphate and UDP-glucose (the OtsA-OtsB pathway) from glycogen-like alpha(1-->4)-linked glucose polymers (the TreY-TreZ pathway) and from maltose (the TreS pathway). Each of the pathways was found to be active in both rapid-growing Mycobacterium smegmatis and slow-growing Mycobacterium bovis BCG. The presence of a disrupted treZ gene in Mycobacterium leprae suggests that this pathway is not functional in this organism. The presence of multiple biosynthetic pathways indicates that trehalose plays an important role in mycobacterial physiology.