Femtomolar Ln(III) Affinity in Peptide-Based Ligands Containing Unnatural Chelating Amino Acids

Abstract

The incorporation of unnatural chelating amino acids in short peptide sequences leads to lanthanide-binding peptides with a higher stability than sequences built exclusively from natural residues. In particular, the hexadentate peptide P(22), which incorporates two unnatural amino acids Ada(2) with aminodiacetate chelating arms, showed picomolar affinity for Tb(3+). To design peptides with higher denticity, expected to show higher affinity for Ln(3+), we synthesized the novel unnatural amino acid Ed3a(2) which carries an ethylenediamine triacetate side-chain and affords a pentadentate coordination site. The synthesis of the derivative Fmoc-Ed3a(2)(tBu)(3)-OH, with appropriate protecting groups for direct use in the solid phase peptide synthesis (Fmoc strategy), is described. The two high denticity peptides P(HD2) (Ac-Trp-Ed3a(2)-Pro-Gly-Ada(2)-Gly-NH(2)) and P(HD5) (Ac-Trp-Ada(2)-Pro-Gly-Ed3a(2)-Gly-NH(2)) led to octadentate Tb(3+) complexes with femtomolar stability in water. The position of the high denticity amino acid Ed3a(2) in the hexapeptide sequence appears to be critical for the control of the metal complex speciation. Whereas P(HD5) promotes the formation of polymetallic species in excess of Ln(3+), P(HD2) forms exclusively the mononuclear complex. The octadentate coordination of Tb(3+) by both P(HD) leads to total dehydration of the metal ion in the mononuclear complexes with long luminescence lifetimes (>2 ms). Hence, we demonstrated that unnatural amino acids carrying polyaminocarboxylate side-chains are interesting building blocks to design high affinity Ln-binding peptides. In particular the novel peptide P(HD2) forms a unique octadentate Tb(3+) complex with femtomolar stability in water and an improvement of the luminescence properties with respect to the trisaquo TbP(22) complex by a factor of 4.

Rationally designed mineralization for selective recovery of the rare earth elements

“…The Asp9 backbone and acidic side chains were especially sensitive, with signals significantly diminished, even at the lowest Dy 3+ concentration. This result clearly indicates that the coordination of Dy 3+ by the carboxylate occurs first during reaction with Lamp, which is similar to the features observed for chelation with Ln 3+ (refs 36 , 39 , 40 ). Increasing the concentration of Dy 3+ to 2 μM resulted in the disappearance of half the NH resonances, mainly those of C-terminal residues ( Supplementary Figs 11 and 12 ).…”

“…13 ), similar to the pattern observed for Dy 3+ titration, indicate that interaction with Ln 3+ occurs mainly at the C-terminal and acidic residues. The binding affinity of this stage was calculated as K D =58.6 μM, which indicates that this is a comparatively weaker interaction than reported for various chelating molecules 36 39 40 41 . In the second phase, excess La 3+ led to further changes in some residues, including Leu6, Trp7, Asp14, Phe15, Leu16 and Ser18 ( Fig.…”

New 4-hydroxy-N-(2-hydroxyethyl)butanamides: Structure and acidity

“…Isomer 7(2S,5R,6S) crystallised from THF, mp 118-120°C. NMR (DMSO-d 6 , 25°C, d ppm) 1 H: 7a) 2.29 (br s, 6.8, 6.6, 1H, H2), 1.32 (dt, 6.8, 6.5, 2H, H3), 3.30 (t, 6.5, 4H, H4), 3 …”

“…The design of new metal complexes based on amides ligands derived from unnatural aminoacids is an active research field [3]. The complexes of metal ions and peptides have application as chemosensors [4,5] and as binding and photocleavage of DNA [6] between many other applications.…”

“…Ligands bearing hydroxyl groups as coordinative arms are also relevant because they are able to coordinate many metals of biological activity [8] and can be used to remove them from intracellular or extracellular spaces. They can also employed as chelating agents for toxic metals or in chelation therapies reducing the toxic effects of metals [3].…”