Direct Observation of Structural Heterogeneity in a β-Sheet

Structural heterogeneity is thought to be inherent in many proteins and may be important for their folding and/or function. However, it is difficult to detect by conventional methods. Carbon−deuterium bonds are environmentally sensitive, nonperturbative probes of protein environments whose observation and characterization are facilitated by their unique stretching absorption frequency in an otherwise unobscured region of the IR spectrum. We demonstrate that deuterium atoms incorporated at Cα backbone positions (Cα−D bonds) are sensitive to the local backbone structure and thus may be used not only to detect structural heterogeneity but also to help characterize it structurally. Density functional theory calculations are used to predict that Cα−D bonds of glycine are sensitive to their local structure, with the absorptions red-shifted for an extended β-sheet relative to γ- and α-helix-like turns. These predictions are confirmed using the N-terminal Src homology 3 (nSH3) domain from the human CrkII adaptor ...