Denatured Ensemble 1H, 13C and 15N Chemical Shift Values for Amino Acid Residues in a Glycine-Rich Protein

Glycine rich segments are common in disordered protein regions such as the spacer segments of biomolecular condensates. However, glycine rich segments can also adopt polyproline II (PPII) helices which form ordered bundles in natural folded proteins or protein domains. Whereas NMR chemical shifts are widely used to identify and quantify α-helices, β-strands and disorder conformations, appropriate chemical shift reference values for glycine-rich segments are still lacking. To address this issue, we have measured the backbone 1HN, 1HA, 13CA, 13CB and 15N chemical shifts of all twenty common natural amino acids in the context of a designed disordered glycine-rich protein named “Glyzilla”. Glyzilla is thoroughly disordered according to its far UV-CD spectra, small 13CA conformational chemical shifts and a lack of NOEs. Nevertheless, significant differences are observed for its glycine 1HN and 15N chemical shift values relative to the chemical shift values predicted for a statistical coil. By incorporating these differences into theoretical models, the prediction of statistical coil versus PPII helix for glycine-rich tracts could be improved.