Avidin host protein

Chem. Soc., 126, 14411-14418 Skander, M., Malan, C., Ivanova, A. and Ward, TR. (2005) Chemical optimization of artificial metaUoenzymes based on the biotin-avidin technology (S)-selective and solvent-tolerant hydrogenation catalysts via the introduction of chiral amino acid spacers. Chem. Commun., 4815-4817 Ward, TR. (2005) Artificial metallo-enzymes for enantioselective catalysis based on the noncovalent incorporation of organometallic moieties in a host protein. Chem.-Eur. J., 11, 3798-3804 Letondor, C. and Ward, TR. (2006) Artificial metaUoenzymes for enantioselective catalysis Recent advances. Chem. Bio. Chem., 7, 1845-1852. 

Letondor, C., Humbert, N. and Ward, TR. (2005) Artificial metaUoenzymes based on biotin-avidin technology for the enantioselective reduction of ketones by transfer hydrogenation. Proc. Natl. Acad. Sci. U.S.A., 102, 4683-4687 Letondor, C., Pordea, A., Humbert, N., Ivanova, A., Mazurek, S., Novic, M. and Ward, TR. (2006) Artificial transfer hydrogenases based on the biotin-(strept)avidin technology Fine tuning the selectivity by saturation mutagenesis of the host protein. J. Am. Chem. Soc., 128, 8320-8328. 

FIGURE 28 Artificial metalloenzymes (A) strategy for incorporating a catalytically active metal fragment into a host protein (Wilson and Whitesides (97)) (B) hydrogenation of alkenes via biotin-(strep)avidin methodology (Wilson and Whitesides (97) and Skander et al. (9S)). (For a color version of this figure, the reader is referred to the Web version of this chapter.)... 

Letondor C, Pordea A, Humbert N, Ivanova A, Mazurek S, Novic M, Ward TR. Artificial transfer hydrogenases based on the biotin-(strept)avidin technology fine tuning the selectivity by saturation mutagenesis of the host protein. J. Am. Chem. Soc. 2006 128 8320-8328. 

Fig. 2 Biotin-avidin technology Artificial metalloenzymes [M(L )(biotin-ligand)]c(strept)avidin for enantioselective catalysis are based on the anchoring of a catalyticaUy active metal fragment within a host protein via a hgand, a spacer, and biotin. Chemical optimization can be achieved either by varying the spacer or the metal chelate moiety ML ). Saturation mutagenesis at a position close to the metal moiety ( ) can be used for genetic optimization...

A metal complex with a host protein using a combination of avidin as a protein and biotin with a rhodium diphosphine complex was prepared as a supramolecular asymmetric catalyst. Avidin shows a high affinity for biotin K = -10 M- ), indicating that the rhodium diphosphine complex quantitatively binds into the chiral space of avidin. 

These examples are part of a broader design scheme to combine catalytic metal complexes with a protein as chiral scaffold to obtain a hybrid catalyst combining the catalytic potential of the metal complex with the enantioselectivity and evolvability of the protein host [11]. One of the first examples of such systems combined a biotinylated rhodium complex with avidin to obtain an enantioselective hydrogenation catalyst [28]. Most significantly, it has been shovm that mutation-based improvements of enantioselectivity are possible in these hybrid catalysts as for enzymes (Figure 3.7) [29]. 

Artificial metalloenzymes, as reviewed here, are hybrid catalysts resulting from the introduction of a metal complex with catalytic activity into a macromolecular host, avidin or streptavidin (referred to as (strept)avidin hereafter). This provides a well-defined enantiopure second coordination sphere, thus potentially inducing selectivity in the catalyzed reaction [2-16], The incorporation of an organometallic moiety within a protein may combine the advantages of both catalytic strategies, which are, in many regards, complementary (Table 1). 

Considering the ease of recombinant protein production in various hosts, we set out to produce streptavidin (Sav hereafter) in Escherichia coli and avidin (Avi hereafter) in Pichia pastoris Although in our hands both proteins could be overexpressed to high levels (230mgl cell culture and 330mgl cell culture respectively) streptavidin was eventually preferred over avidin for the following reasons ... 

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