Solution structures of glycosylated family 1 carbohydrate binding modules

Here we have determined the solution structures of glycosylated Family 1 Cellulose Binding Modules (CBM) using Nuclear Magnetic Resonance spectroscopy (NMR). Native Family 1 CBMs are post-translationally glycosylated at Thr1 and Ser3 with mannose groups when expressed in T. reesei. Understanding how the glycosylation affects the structure and function is of particular importance given its conservation in Family 1 CBMs. Two samples were studied by NMR: a natively glycosylated Family 1 CBM with a mannose group attached to both Thr1 and Ser3, and the engineered Family 1 CBM with single mannose groups attached to Thr1, Ser3 and Ser14. Glycosylation of Ser14 on Family 1 CBMs has been shown to greatly impact binding affinity and the structures presented here confirm that a mannose residue on Ser14 can align with the binding face of Family 1 CBMs to provide additional interactions including hydrogen bonding potential with cellulose, accounting for the increase in binding affinity.