Neutron Diffraction Studies on Proteins Give Insight into Local Hydrogen-Bonding Flexibility

9 Neutron Diffraction Studies on Proteins Give Insight into Local Hydrogen-Bonding Flexibility 

The H/D exchange occurs when a proton involved in hydrogen bonding is accessible to solvent (D20), and is irreversible due to the large excess of D20 in the sample  

The H/D exchange pattern for peptide N-H groups of crystalline trypsin, displayed schematically in Fig. 19.17, shows clearly that the H/D exchange is not evenly distributed among secondary N-H - -0=C hydrogen bonds. Some are fully 

A case of special interest in the trypsin H/D exchange experiment is the Ser54 hydroxyl bridged N-H 0 contact between peptide groups 55N-H and 43C=0  

Whereas NMR can be used to study exchange kinetics, neutron diffraction can provide only long-term information because the soaking of crystals in D20 and data collection takes of the order of months. In a recent diffraction study where certain neutron diffraction intensities were monitored, the D2O/H2O exchange with time could be followed directly [637]. While this provides insight into the overall exchange in a crystal, individual H/D exchange rates cannot be observed. For this, NMR methods have to be applied. 

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