pH dependent binding in de novo hetero bimetallic coiled coils

Abstract

a Herein the first example of a bimetallic coiled coil featuring a lanthanide binding site is reported, opening opportunities to exploit the attractive NMR and photophysical properties of the lanthanides in multi metallo protein design. In our efforts to fully characterise the system we identified for the first time that lanthanide binding to such sites is pH dependent, with optimal binding at neutral pH, and that the double AsnAsp site is more versatile in this regard than the single Asp site. Our second site featured the structural HgCys 3 site, the chemistry of which was essentially unaltered by the presence of the lanthanide site. In fact, both metal binding sites within the hetero bimetallic coiled coil displayed the same properties as their mononuclear single binding site controls, and operated independently of each other. Finally, pH can be used as an external trigger to control the binding of Hg(II) and Tb(III) to the two distinct sites within this coiled coil, and offers the opportunity to "activate" metal binding sites within complex multi metallo and multi-functional designs.

De novodesigned coiled coils as scaffolds for lanthanides, including novel imaging agents with a twist

“…Similar observations were made for the MB1-2 peptide, although the pH range through which Tb 3+ was bound was considerably larger (pH 4 -7). 119…”

“…130 Only one example of a lanthanide-containing hetero-bimetallic coiled coil has thus far been reported. 119 The coiled coil features a lanthanide binding Asp 3 site as well as a thiolate Cys 3 site, suitable for binding softer metal ions including mercury. 90,131 The soft thiol ligands contrast with the hard oxygen donors associated with lanthanide-binding, and provide a mechanism by which selectivity can be readily achieved based on hard-soft acid base theory.…”

Location‐Dependent Lanthanide Selectivity Engineered into Structurally Characterized Designed Coiled Coils

“…Although Ln 3+ coiled coils display selectivity for Ln 3+ ions over Ca 2+ , [7c–f] there have been no studies relating to selectivity across the lanthanide series. Given the desire to distinguish between the different lanthanide ions, and the reports of coiled coils capable of metal ion discrimination based on size, [14] the presence of lone pairs, [15] and hard soft acid base theory, [2a, 16] we set out to establish whether size‐selective Ln 3+ binding sites can be engineered into coiled coils, and to obtain crucial, and currently lacking, structural information regarding Ln 3+ coiled coils.…”

Coiled coils 9-to-5: rational de novo design of α-helical barrels with tunable oligomeric states

“…We also avoided cysteine because of potential issues with redox chemistry and to reserve it for introducing function in follow-on studies. 11,19,20…”