Streptavidin host protein

With the most advanced streptavidin variants, the strategy in which a racemic catalyst is converted to a chiral-at-metal complex and then further assisted by residues in the chiral protein has led to the development of both R- and 5-selective synthetic enzymes for imine reduction. Extensive kinetic data has been obtained for these new synthetic enzymes, and computer modelling of the complex stmctures (which contain four interacting subunits) serves to support and understand the results. An induced lock and key where the host protein structure determines the catalyst structure and the reduction selectivity is proposed (Fig. 44) [141]. 

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). 

Proteins as Host for Enantioselective Catalysis Artificial Metalloenzymes Based on the Biotin-Streptavidin Technology... 

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 ... 

It has been demonstrated that CNTs can enhance crystallinity of certain host polymers (72, 95), leading to improved mechanical properties. The CNT-enhanced nucleation crystallinity has been reported to occur in various polymer systems, including poly(vinyl alcohol) (PVA), polycarbonate (PC), polypropylene (PP), and poly(m-phenylenevinylene-co-2,5-dioctyloxy-p-phenylenevinylene) (PmPV) (98-111). In addition to these synthetic polymers, certain proteins, such as streptavidin, were also found to form crystalline structures around CNTs (100, 102, 104). Of particular interest is that polyvinyl alcohol (PVA), which showed significant improvement in mechanical properties... 

In the absence of any pre-purification step, it might be intuitively expected that host cell proteins which are endogenously biotinylated would compete with the biotinylated recombinant proteins for the available streptavidin-binding sites on the array surface. Insect cells have five such endogenous proteins, but under native conditions we have observed that these protein do not compete efficiently with biotinylated recombinant proteins for binding to streptavidin. This perhaps reflects low natural expression levels and the fact that in endogenous biotinylated protein, the biotin is typically less solvent accessible in the native protein (30) meaning that the biotin may not be physically accessible to bind to streptavidin. 

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