Determination of the solution conformation of D-gluco-dihydroacarbose, a high-affinity inhibitor bound to glucoamylase by transferred NOE NMR spectroscopy

The determination of the bound solution conformation of D-gluco-dihydroacar bose (GAC), a tight-binding inhibitor of several glycosidase and amylase en zymes, by glucoamylase is described. Transferred NOE NMR experiments and li ne-broadening effects indicate that GAC is bound in a conformation resembli ng that observed in the crystal structure. This contrasts with the predomin ant conformation of GAC when free in solution. The NMR results also suggest regions on the carbohydrate that are in close contact with the protein. Th e determination of the bound solution conformation of GAC by glucoamylase u sing transferred NOE (trNOE) measurements is a significant achievement give n the high affinity constant (k(a) = 3 x 10(7) M-1) for this receptor-ligan d pair. It is striking that the off-rate for complexation is still sufficie ntly high to permit observation of trNOEs. (C) 2000 Elsevier Science Ltd. A ll rights reserved.