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标题：Combined ligand-observe 19F and protein-observe 15N,1H-HSQC NMR suggests phenylalanine as the key Δ-somatostatin residue recognized by human protein disulfide isomerase
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作者：Kirsty L. Richards ; Michelle L. Rowe ; Paul B. Hudson 等
期刊名称：Scientific Reports
电子版ISSN：2045-2322
出版年度：2016
卷号：6
期号：1
DOI：10.1038/srep19518
语种：English
出版社：Springer Nature
摘要：Human protein disulphide isomerase (hPDI) is an endoplasmic reticulum (ER) based isomerase and folding chaperone. Molecular detail of ligand recognition and specificity of hPDI are poorly understood despite the importance of the hPDI for folding secreted proteins and its implication in diseases including cancer and lateral sclerosis. We report a detailed study of specificity, interaction and dissociation constants (K_d) of the peptide-ligand Δ-somatostatin (AGSKNFFWKTFTSS) binding to hPDI using ¹⁹F ligand-observe and ¹⁵N,¹H-HSQC protein-observe NMR methods. Phe residues in Δ-somatostatin are hypothesised as important for recognition by hPDI therefore, step-wise peptide Phe-to-Ala changes were progressively introduced and shown to raise the K_d from 103 + 47 μM until the point where binding was abolished when all Phe residues were modified to Ala. The largest step-changes in K_d involved the F11A peptide modification which implies the C-terminus of Δ-somatostatin is a prime recognition region. Furthermore, this study also validated the combined use of ¹⁹F ligand-observe and complimentary ¹⁵N,¹H-HSQC titrations to monitor interactions from the protein’s perspective. ¹⁹F ligand-observe NMR was ratified as mirroring ¹⁵N protein-observe but highlighted the advantage that ¹⁹F offers improved K_d precision due to higher spectrum resolution and greater chemical environment sensitivity.