Artificial Metalloenzymes:  (Strept)avidin as Host for Enantioselective Hydrogenation by Achiral Biotinylated Rhodium−Diphosphine Complexes

Abstract

We report on the generation of artificial metalloenzymes based on the noncovalent incorporation of biotinylated rhodium-diphosphine complexes in (strept)avidin as host proteins. A chemogenetic optimization procedure allows one to optimize the enantioselectivity for the reduction of acetamidoacrylic acid (up to 96% ee (R) in streptavidin S112G and up to 80% ee (S) in WT avidin). The association constant between a prototypical cationic biotinylated rhodium-diphosphine catalyst precursor and the host proteins was determined at neutral pH: log K(a) = 7.7 for avidin (pI = 10.4) and log K(a) = 7.1 for streptavidin (pI = 6.4). It is shown that the optimal operating conditions for the enantioselective reduction are 5 bar at 30 degrees C with a 1% catalyst loading.

Hierarchical Self‐Assembly of One‐Dimensional Streptavidin Bundles as a Collagen Mimetic for the Biomineralization of Calcite

“…The biotin-binding event between the [Fe(Biot 2 -terpy) 2 ] 2+ ion and Sav can be conveniently monitored with the disappearance of an induced CD signal, l max = 505 nm, caused by the displacement of 2-(4'-hydroxyazobenzene)benzoic acid (HABA, a hydrophobic dye weakly bound within the biotin-binding pocket) by the [Fe(Biot 2 -terpy) 2 ] 2+ ion (see the Supporting Information). [37,49] Upon standing at room temperature, the dilute purple solution containing the metal + ligand + protein triad slowly becomes turbid, suggesting the formation of polymeric material {[Fe(Biot 2 -terpy) 2 ] 2+ &Sav} 1 . In the presence of calcium ions (0.05 m), threads appear within minutes and can be visualized by scanning electron microscopy (SEM, Figure 3 a,b).…”

Artificial Metalloenzymes: Proteins as Hosts for Enantioselective Catalysis

“…41 For this purpose, the tetrameric streptavidin was loaded with increasing amounts of [Rh(COD)(Biot-1)] + (1-10 equivalents). Beyond four equivalents of coenzyme, the optical purity of the produced acetamidoalanine steadily decreases, as the catalyst outside of the protein affords essentially racemic material.…”

Hierarchical Self‐Assembly of One‐Dimensional Streptavidin Bundles as a Collagen Mimetic for the Biomineralization of Calcite

“…[35][36][37][38][39][40][41] Streptavidin is a slightly acidic (isoelectric point, pI = 6.3) homotetrameric protein that bears four biotin binding sites. [42,43] For this proof-ofprinciple study, we selected a preorganized bis-biotinylated terpyridine ligand Biot 2 -terpy that binds to two cis-related sites in streptavidin.…”

“…[44][45][46][47] A ferrous ion was chosen as terpyridine binds in a cooperative fashion (K 1 = 1.26 10 7 m À1 , K 2 = 6.31 10 13 m À1 ), [48] thus ensuring the exclusive formation of a linear connector bearing four biotin anchors ( Figure 2 2+ ion and Sav can be conveniently monitored with the disappearance of an induced CD signal, l max = 505 nm, caused by the displacement of 2-(4'-hydroxyazobenzene)benzoic acid (HABA, a hydrophobic dye weakly bound within the biotin-binding pocket) by the [Fe(Biot 2 -terpy) 2 ] 2+ ion (see the Supporting Information). [37,49] Upon standing at room temperature, the dilute purple solution containing the metal + ligand + protein triad slowly becomes turbid, suggesting the formation of polymeric material {[Fe(Biot 2 -terpy) 2 ] 2+ &Sav} 1 . In the presence of calcium ions (0.05 m), threads appear within minutes and can be visualized by scanning electron microscopy (SEM, Figure 3 a,b).…”