Perfluoro-tert-butyl Homoserine Is a Helix-Promoting, Highly Fluorinated, NMR-Sensitive Aliphatic Amino Acid: Detection of the Estrogen Receptor·Coactivator Protein-Protein Interaction by19F NMR.
Highly fluorinated amino acids can stabilize proteins and complexes with proteins, via enhanced hydrophobicity, and provide novel methods for identification of specific molecular events in complex solutions, via selective detection by19F NMR and the absence of native19F signals in biological contexts. However, the potential applications of19F NMR in probing biological processes are limited both by the strong propensities of most highly fluorinated amino acids for the extended conformation and by the relatively modest sensitivity of NMR spectroscopy, which typically constrains measurements to mid-micromolar concentrations. Herein, we demonstrate that perfluoro-tert-butyl homoserine exhibits a propensity for compact conformations, including α-helix and polyproline helix (PPII), that is similar to that of methionine. Perfluoro-tert-butyl homoserine has nine equivalent fluorines that do not couple to any other nuclei, resulting in a sharp singlet that can be sensitively detected rapidly at low micromolar concentrations. Perfluoro-tert-butyl homoserine was incorporated at sites of leucine residues within the α-helical LXXLL short linear motif of estrogen receptor (ER) coactivator peptides. A peptide containing perfluoro-tert-butyl homoserine at position i + 3 of the ER coactivator LXXLL motif exhibited a Kdof 2.2 μM for the estradiol-bound estrogen receptor, similar to that of the native ligand.19F NMR spectroscopy demonstrated the sensitive detection (5 μM concentration, 128 scans) of binding of the peptide to the ER and of inhibition of protein-protein interaction by the native ligand or by the ER antagonist tamoxifen. These results suggest diverse potential applications of perfluoro-tert-butyl homoserine in probing protein function and protein-protein interfaces in complex solutions.
Department of Chemistry and Biochemistry, University of Delaware , Newark, Delaware 19716, United States.
Caitlin M
CM
Tressler
Department of Chemistry and Biochemistry, University of Delaware , Newark, Delaware 19716, United States.
Neal J
0000-0002-7417-8085
NJ
Zondlo
D000595:Amino Acid Sequence; D047628:Estrogen Receptor alpha / Q000737:chemistry* / Q000378:metabolism*; D054879:Halogenation; D006714:Homoserine / Q000031:analogs & derivatives* / Q000737:chemistry* / Q000494:pharmacology*; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D011485:Protein Binding; D000072756:Protein Conformation, alpha-Helical; D000072417:Protein Domains; D005466:Fluorocarbons
D047628:Estrogen Receptor alpha; D006714:Homoserine; C000618856:perfluoro-tert-butyl homoserine; D005466:Fluorocarbons