Biocompatibility and Therapeutic Potential of Glycosylated Albumin Artificial Metalloenzymes
The ability of natural metalloproteins to prevent inactivation of their metal cofactors by biological metabolites, such as glutathione, is an area that has been largely ignored in the field of artificial metalloenzyme (ArM) development. Yet, for ArM research to transition into future therapeutic applications, biocompatibility remains a crucial component. The work presented here shows the creation of a human serum albumin-based ArM that can robustly protect the catalytic activity of a bound ruthenium metal, even in the presence of 20 mM glutathione under in vitro conditions. To exploit this biocompatibility, the concept of glycosylated artificial metalloenzymes (GArM) was developed, which is based on functionalizing ArMs with N-glycan targeting moieties. As a potential drug therapy, this study shows that ruthenium-bound GArM complexes could preferentially accumulate to varying cancer cell lines via glycan-based targeting for prodrug activation of the anticancer agent umbelliprenin using ring-closing metathesis.
Library Design and Screening Protocol for Artificial Metalloenzymes Based on the Biotin-Streptavidin Technology
Artificial metalloenzymes (ArMs) based on the incorporation of a biotinylated metal cofactor within streptavidin (Sav) combine attractive features of both homogeneous and enzymatic catalysts. To speed up their optimization, we present a streamlined protocol for the design, expression, partial purification and screening of Sav libraries. Twenty-eight positions have been subjected to mutagenesis to yield 335 Sav isoforms, which can be expressed in 24-deep-well plates using autoinduction medium. The resulting cell-free extracts (CFEs) typically contain >1 mg of soluble Sav. Two straightforward alternatives are presented, which allow the screening of ArMs using CFEs containing Sav. To produce an artificial transfer hydrogenase, Sav is coupled to a biotinylated three-legged iridium pianostool complex Cp*Ir(Biot-p-L)Cl (the cofactor). To screen Sav variants for this application, you would determine the number of free binding sites, treat them with diamide, incubate them with the cofactor and then perform the reaction with your test compound (the example used in this protocol is 1-phenyl-3,4-dihydroisoquinoline). This process takes 20 d. If you want to perform metathesis reactions, Sav is coupled to a biotinylated second-generation Grubbs-Hoveyda catalyst. In this application, it is best to first immobilize Sav on Sepharose-iminobiotin beads and then perform washing steps. Elution from the beads is achieved in an acidic reaction buffer before incubation with the cofactor. Catalysis using your test compound (in this protocol, 2-(4-(N,N-diallylsulfamoyl)phenyl)-N,N,N-trimethylethan-1-aminium iodide) is performed using the formed metalloenzyme. Screening using this approach takes 19 d.
Metal: IrReaction: Transfer hydrogenationMax TON: 183ee: 71PDB: ---Notes: Purified streptavidin (mutant K121A)
Metal: IrReaction: Transfer hydrogenationMax TON: 42ee: 59PDB: ---Notes: Cell free extract (mutant Sav K121A) treated with diamide
Ligand type: N-heterocyclic carbeneMax TON: 66ee: ---PDB: ---Notes: Purified streptavidin (mutant K121A)