Synthesizes trehalose from ADP-, UDP- or GDP-glucose and glucose. an NDP-alpha-D-glucose + D-glucose = a ribonucleoside 5'-diphosphate + alpha,alpha-trehalose + H(+) Optimum pH is 5.5. Stable from pH 5 to pH 8. Not thermostable. Approximately 25% of maximum activity remains after 1 hour incubation at 55 degrees Celsius. Homodimer. Belongs to the glycosyltransferase group 1 family. Glycosyltransferase 4 subfamily.