540 Chemie und zugeordnete Wissenschaften
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The impact of the incorporation of a non-natural amino acid (NNAA) on protein structure, dynamics, and ligand binding has not been studied rigorously so far. NNAAs are regularly used to modify proteins post-translationally in vivo and in vitro through click chemistry. Herein, structural characterisation of the impact of the incorporation of azidohomoalanine (AZH) into the model protein domain PDZ3 is examined by means of NMR spectroscopy and X-ray crystallography. The structure and dynamics of the apo state of AZH-modified PDZ3 remain mostly unperturbed. Furthermore, the binding of two PDZ3 binding peptides are unchanged upon incorporation of AZH. The interface of the AZH-modified PDZ3 and an azulene-linked peptide for vibrational energy transfer studies has been mapped by means of chemical shift perturbations and NOEs between the unlabelled azulene-linked peptide and the isotopically labelled protein. Co-crystallisation and soaking failed for the peptide-bound holo complex. NMR spectroscopy, however, allowed determination of the protein-ligand interface. Although the incorporation of AZH was minimally invasive for PDZ3, structural analysis of NNAA-modified proteins through the methodology presented herein should be performed to ensure structural integrity of the studied target.
The excellent results of dispersion‐corrected density functional theory (DFT‐D) calculations for static systems have been well established over the past decade. The introduction of dynamics into DFT‐D calculations is a target, especially for the field of molecular NMR crystallography. Four 13C ss‐NMR calibration compounds are investigated by single‐crystal X‐ray diffraction, molecular dynamics and DFT‐D calculations. The crystal structure of 3‐methylglutaric acid is reported. The rotator phases of adamantane and hexamethylbenzene at room temperature are successfully reproduced in the molecular dynamics simulations. The calculated 13C chemical shifts of these compounds are in excellent agreement with experiment, with a root‐mean‐square deviation of 2.0 ppm. It is confirmed that a combination of classical molecular dynamics and DFT‐D chemical shift calculation improves the accuracy of calculated chemical shifts.