Trehalose Metabolism

So far, five different biosynthetic pathways for trehalose have been described (Fig. 14.2). The most extensively distributed was discovered about 50 years ago by Cabib and Lenoir (1958), and since then, it has been described in diverse organisms including eubacteria, archaea, fungi, insects, and plants:

1. This pathway is constituted by two enzymatic steps catalyzed by trehalose-6-phosphate synthase (TPS) and trehalose-phosphatase (TPP). TPS transfer glucose from UDP-glucose to glucose 6-phosphate generating trehalose 6-phosphate (T6P) and UDP, while TPP dephosphorylates T6P to trehalose and inorganic phosphate (De Smet et al. 2000; Elbein et al. 2003) .

2. Reported in thermophilic archaea of the genus Sulfolobus the second pathway consists in the conversion of maltodextrines (maltooligosac-charides, glycogen and starch) to trehalose. This pathway is catalyzed by maltooligosyl tre-halose synthase (TreY), coded by the treY gene, and maltooligosyl trehalose trehalohydrolase (TreZ), coded by the treZ gene that catalyzes the hydrolytic release of trehalose from maltoo-ligosyltrehalose, which contains a trehalose moiety at the end of the polymer (Elbein et al. 2003; Streeter and Bhagwat 1999).

3. First reported in Pimelobacter sp., orthologs of the third pathway has been found in other eubacteria. In this pathway maltose is isomer-ized to trehalose by the enzyme trehalose synthase (TS) (Higashiyama 2002; Elbein et al. 2003) .

4. The fourth pathway consists in the reversible hydrolysis of trehalose in the presence of inorganic phosphate by trehalose phosphory-lase (TreP), present in some fungi. In this reaction the transfer of a glucose molecule to a phosphate generates glucose 1-phosphate and releases the other glucose residue. It is

Fig. 14.2 Known pathways of trehalose synthesis and MOTS maltooligosyltrehalosesynthase, MOTT maltooli-

catabolism in eukaryotes and prokaryotes. UDP uridine gosyl trehalose tetrahydrolase, TS trehalose synthase, diphosphate, Glucose-6-P glucose 6-phosphate, TPS tre- Glucose-1-P glucose 1-phosphate, TreP trehalose phos-

halose phosphate synthase, Trehalose-6-P trehalose phorylase, TreT trehalose glycosyltransferring synthase,

6-phosphate, TPP trehalose phosphate phosphatase, Tre trehalase

Fig. 14.2 Known pathways of trehalose synthesis and MOTS maltooligosyltrehalosesynthase, MOTT maltooli-

catabolism in eukaryotes and prokaryotes. UDP uridine gosyl trehalose tetrahydrolase, TS trehalose synthase, diphosphate, Glucose-6-P glucose 6-phosphate, TPS tre- Glucose-1-P glucose 1-phosphate, TreP trehalose phos-

halose phosphate synthase, Trehalose-6-P trehalose phorylase, TreT trehalose glycosyltransferring synthase,

6-phosphate, TPP trehalose phosphate phosphatase, Tre trehalase unclear whether TreP enzyme participates in the synthesis or degradation of trehalose, since the biosynthetic reaction has only been shown in vitro (Wannet et al. 1998; Schiraldi et al. 2002).

5. The last biosynthetic pathway for trehalose consists in the reversible formation of trehalose from ADP-glucose and glucose and was discovered in the hyperthermophilic archaeon Thermococcus litoralis (Qu et al. 2004; Ryu et al. 2005). This reaction is catalyzed by the trehalose glycosyl-transferring synthase (TreT), which can also use UDP-glucose and GDP-glucose, although it is less efficient with these substrates. Trehalose catabolism in two glucose molecules is catalyzed by trehalase enzyme activity (Tre) that has been found in a variety of organisms including prokaryotic and eukaryotic (Elbein 1974) ; Trehalase is ubiquitous in higher plants, and it is likely that trehalase is the sole route of trehalose breakdown in plants, as trehalose accumulates in the presence of specific trehalase inhibitor validamycin A (Müller et al. 2001).

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