The binding of antibiotics to ERp57/GRP58

The effects of five antibiotics, previously described as ligands of protein disulfide isomerase PDI, have now been studied on the homologous protein ERp57. They bind to this protein with much higher affinity than to PDI, and some of them inhibit the reductase and the DNA-binding activities of ERp57. In view of the high affinity of vancomycin, erythromycin and streptomycin, some effects of their interaction with this protein might be expected in vivo

Combined ligand-observe 19F and protein-observe 15N,1H-HSQC NMR suggests phenylalanine as the key ?-somatostatin residue recognized by human protein disulfide isomerase.

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 (Kd) of the peptide-ligand ?-somatostatin (AGSKNFFWKTFTSS) binding to hPDI using 19F ligand-observe and 15N,1H-HSQC protein-observe NMR methods. Phe residues in ?-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 Kd from 103?+?47??M until the point where binding was abolished when all Phe residues were modified to Ala. The largest step-changes in Kd involved the F11A peptide modification which implies the C-terminus of ?-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 Kd precision due to higher spectrum resolution and greater chemical environment sensitivity