Tertiary protein structure angle constraints

Concepts with which to construct three-dimensional structure from sohd-state NMR data are currently being developed in many laboratories. All of these approaches aim at determining both the secondary structure (the backbone conformation) and tertiary structure (the overall fold) of proteins in an efficient manner. As in the solution state, solid-state NMR structure determination involves the calculation of families of molecular conformations that are consistent with the experimentally derived distance and/or angle constraints. The number and precision of these parameters determine the accuracy of the resulting three-dimensional structure. 

Besides the NOE, the NMR technique offers other information that can also be used in structure determination. Spin-spin coupling constants are a traditional source of such information, and it is becoming increasingly clear that the chemical shifts in proteins and nucleic acids can often give direct information on the secondary and tertiary structure since they depend upon the local environment. This additional NMR information can be used at several levels. Coupling constant information is often converted to dihedral angle constraints and used in a manner similar to the distance constraints derived from NOE information. Because of the complexity of the interactions that influence the chemical shift, this information is more useful at the final structure refinement stage, where the overall structure has already been determined. 

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