Leucine Side-Chain Conformation and Dynamics in Proteins from 13C NMR Chemical Shifts



Look to the left: The carbon nucleus of a substituent in the gauche position about a subtending dihedral angle experiences an NMR chemical shift of about 5 ppm relative to the same chemical group present in the trans position. We demonstrate that this “γ-gauche effect” can be utilized to determine the conformation and extent of rotameric averaging for leucine amino acid side chains in the protein calbindin D9k. The success of this approach suggests that rules can be established to define the orientation of other side chains in proteins as well, offering an easy gauge of protein side-chain flexibility, as well as avenues to advance protein structure determination by using side-chain chemical shifts.

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