¹H and ¹⁵N Assignments and Secondary Structure of the Starch‐Binding Domain of Glucoamylase from Aspergillus niger

¹H and ¹⁵N NMR resonance assignments of the granular starch‐binding domain (SBD) of glucoamylase from Aspergillus niger have been made by multi‐dimensional homonuclear and heteronuclear NMR techniques. Secondary structure analysis based on chemical shifts, ¹H‐¹H NOEs, coupling constants and backbone amide exchange data indicates the presence of a well‐defined β‐sheet structure. This consists of one parallel and five antiparallel pairs of β‐strands forming two β‐sheets. Cis‐trans isomerisation of proline residues and O‐glycosylation of threonine residues are observed and compared between the proteolytically derived SBD fragment and the recombinant protein. Structural features of the SBD in solution were compared to the X‐ray crystal structure of a homologous domain of cyclodextrin glyco‐syltransferase from Bacillus circulans. There are some differences in the locations of the start and end of β‐strands but overall the two structures are very similar. This study will form the basis for the structure determination of the granular SBD and of its complexes.