TreS-Mak-GlgE branched alpha-glucan biosynthesis

A reusable bacterial pathway that channels trehalose into branched alpha-glucan. Trehalose synthase operating in the catabolic direction forms maltose, maltokinase converts maltose to alpha-maltose 1-phosphate, GlgE uses that activated donor to extend alpha-1,4-glucan chains by maltosyl units, and GlgB introduces alpha-1,6 branches. TreS and Mak may be separate proteins or domains of one fusion protein; that architectural variation does not change the four reaction roles.

TreS and Mak occur as separate proteins in some bacteria and as a bifunctional fusion in others. The Pseudomonas putida KT2440 fusion TreSB is therefore represented as the same exemplar in two reaction leaves without collapsing their distinct activities. The module starts with trehalose and ends with branched alpha-glucan; trehalose biosynthesis, glucan priming, degradation, and downstream storage or envelope roles are outside its boundary. Exact EC and Rhea reactions preserve the substrate specificity that the available broad GO terms for Mak and GlgE do not capture. The KT2440 glucose-starvation transcriptome co-upregulates glgA and glgB, which is contextual evidence that GlgB can be shared with the classical GlgA-dependent glycogen route rather than being dedicated to this module.