On the performance of branching enzymes on chemically modified starches

Branching enzymes (BEs; EC 2.4.1.18) catalyze transglycosylation reactions that create branches in native starch and glycogen. While BEs' activity have been extensively studied on native starches, to date their activity on chemically modified starches has not been reported. We demonstrate branching by Rhodothermus obamensis BE (RoBE) on both acetylated and hydroxypropylated starches. Initially, RoBE exhibited a slower rate of branching reaction on chemically modified starches compared to native starch, but over time, it achieved a comparable yield in branching. Additionally, the RoBE reaction was conducted on blends of acetylated and hydroxypropylated starches. MALDI-TOF MS analyses identified the existence of hybrid structures, providing evidence for an inter-transglycosylation reaction pattern. This identification of new pathways for starch modification, will enable the creation of new structures that are challenging to synthesise using conventional processes.