Conformation of methyl .beta.-lactoside bound to the ricin B-chain: interpretation of transferred nuclear Overhauser effects facilitated by spin simulation and selective deuteration

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Abstract
Spin simulation and selective deuteration have been used to aid in the interpretation of 1D transferred nuclear Overhauser effect (TRNOE) NMR experiments on ricin B-chain/ligand systems. Application of these methods has revealed a change in the conformation of deuterated methyl .beta.-lactoside upon binding to the ricin B-chain which results in a slight change in glycosidic torsional angles which appear to dominate in the solution conformation. The combination of simulation and experiment also shows an important sensitivity of TRNOE magnitudes to dissociation rate constants and available spin-diffusion pathways for the ricin B-chain/ligand systems under study. The sensitivity to dissociation rates allows determination of rate constants for methyl .beta.-lactoside and methyl .beta.-galactoside of 50 and 300 s-1, respectively.