alpha,alpha-trehalose-phosphate synthase [UDP-forming]. This enzyme catalyzes the key, penultimate step in biosynthesis of trehalose, a compatible solute made as an osmoprotectant in some species in all three domains of life. The gene symbol OtsA stands for osmotically regulated trehalose synthesis A. Trehalose helps protect against both osmotic and thermal stresses, and is made from two glucose subunits. This model excludes glucosylglycerol-phosphate synthase, an enzyme of an analogous osmoprotectant system in many cyanobacterial strains. This model does not identify archaeal examples, as they are more divergent than glucosylglycerol-phosphate synthase. Sequences that score in the gray zone between the trusted and noise cutoffs include a number of yeast multidomain proteins in which the N-terminal domain may be functionally equivalent to this family. The gray zone also includes the OtsA of Cornyebacterium glutamicum (and related species), shown to be responsible for synthesis of only trace amounts of trehalose while the majority is synthesized by the TreYZ pathway; the significance of OtsA in this species is unclear (see Wolf, et al., PMID:12890033) [Cellular processes, Adaptations to atypical conditions].

Trehalose-6-phosphate synthase [Carbohydrate transport and metabolism]

Trehalose-6-Phosphate Synthase (TPS) is a glycosyltransferase that catalyses the synthesis of alpha,alpha-1,1-trehalose-6-phosphate from glucose-6-phosphate using a UDP-glucose donor. It is a key enzyme in the trehalose synthesis pathway. Trehalose is a nonreducing disaccharide present in a wide variety of organisms and may serve as a source of energy and carbon. It is characterized most notably in insect, plant, and microbial cells. Its production is often associated with a variety of stress conditions, including desiccation, dehydration, heat, cold, and oxidation. This family represents the catalytic domain of the TPS. Some members of this domain family coexist with a C-terminal trehalose phosphatase domain.

Glycosyltransferase family 20. Members of this family belong to glycosyl transferase family 20. OtsA (Trehalose-6-phosphate synthase) is homologous to regions in the subunits of yeast trehalose-6-phosphate synthase/phosphate complex.

alpha,alpha-trehalose-phosphate synthase [UDP-forming]