Abstract 1959 Structure of the Carbohydrate-Binding Module of the Alpha-Amylase AMY3

Starch is a crucial plant carbohydrate, serving as an energy reserve supporting growth and development.Plants have enzymes that regulate starch synthesis and breakdown, with -amylase3 (AMY3) being a plastidic amylase containing a pair of carbohydrate-binding modules CBMs, a feature conserved across plant species.Some enzymes involved in starch remodeling are targeted to specific sites within the starch by the CBMs.This targeting allows for precise control of starch synthesis and degradation.Although many types of CBMs exist, only a few have been studied in detail.Understanding how CBMs work at the molecular level could improve our knowledge of starch remodeling and help develop better tools, like carbohydrate sensors.The -amylase AMY3 from the model plant Arabidopsis thaliana contains an N-terminal CBM.To investigate this CBM, we expressed and purified the N-terminal region of AMY3 containing the CBM from Arabidopsis.Using small-angle X-ray scattering (SAXS) and size exclusion chromatography with multi-angle light scattering (HPLC SEC-MALS), we characterized its structure and size.Our results indicate that the CBM of AMY3 forms dimers, a characteristic that, as far as we are aware, has not been documented for other CBMs.Dimerization is enhanced in the presence of maltodextrins, glucose polymers of approximately 4-28 glucose units.Interestingly, soluble starch contains longer glucose chains and does not increase dimerization like maltodextrin.This suggests that the CBM may bind to starch and prevent cross-linking.