STRESS RESPONSES - Cyanobacteria - page 626

bond thus forming maltooligosyltrehalose which has trehalose at the end of the polymer. The second
enzyme, maltooligosyltrehalose trehalohydolase (TreZ) catalyzes the hydrolytic release of trehalose.
This pathway has been reported in the species of the thermophilic archaebacterium Sulfolobus . The
fourth (TreP) and fi fth (TreT) pathways are reversible pathways that involve the transfer of a glucose
molecule to glucose-1-phosophate and ADP-glucose, respectively. The fourth pathway is mediated
by trehalose phosphorylase (TreP) that has been detected in fungi but its in vivo participation in such
a reaction is uncertain because it has been observed only in vitro . The fi fth pathway is mediated by
trehalose glycosyltransferring synthase (TreT) and it can also use UDP-glucose and GDP-glucose.
This pathway has been reported in the hyperthermophilic archaebacterium Thermococcus litoralis .

A

TPS/TPP PATHWAY

UDP-Glucose

Trehalose

Trehalose 6-phosphate

+

Glucose 6-phosphate

Trehalose 6-Phosphate
Synthase (TPS)

Trehalose 6-Phosphate
Phosphatase (TPP)

B TS PATHWAY

Maltose Trehalose

Trehalose Synthase
(TS)

C TreY/TreZ PATHWAY

Maltooligosylsaccharides
Starch or glycogen

Maltooligosyltrehalose

Trehalose

Maltooligosyl-Trehalose
Synthase (TreY)

Maltooligosyl-Trehalose
Trehalohydrolase (TreZ)

D

TreP PATHWAY

Glucose 1-phosphate Trehalose

+ +

Glucose Pi

Trehalose Phosphorylase
(TreP)

E TreT PATHWAY ADP-Glucose Trehalose

+ +

Glucose ADP

Trehalose Glycosyltransferring
Synthase (TreT)

D-Glucose
+

F TreH PATHWAY

Trehalose

D-Glucose

Trehalase (TreH)

Figure 5: The trehalose biosynthetic pathways. The enzymes are indicated in bold. Dotted arrows in D and E pathways indicate
reversible reaction. With the kind permission of G. Iturriaga, Instituto de Biotecnología-UNAM, Av. Universidad 2001, Col.
Chamilpa, Cuernavaca 62210, Mexico. [Avonce et al. (2006) BMC Evolutionary Biology 6: 109 doi:10.1186/1471-2148-6-109].