Streptavidin and its homologs (together referred to as streptavidin) are widely used in molecular science owing to their highly selective and stable interaction with biotin. Other factors also contribute to the popularity of the streptavidin-biotin system, including the stability of the protein and various chemical and enzymatic biotinylation methods available for use with different experimental designs. The technology has enjoyed a renaissance of a sort in recent years, as new streptavidin variants are engineered to complement native proteins and novel methods of introducing selective biotinylation are developed for in vitro and in vivo applications. There have been notable developments in the areas of catalysis, cell biology, and proteomics in addition to continued applications in the more established areas of detection, labeling and drug delivery. This review summarizes recent advances in streptavidin engineering and new applications based on the streptavidin-biotin interaction.
Previous studies tracking AMPA receptor (AMPAR) diffusion at synapses observed a large mobile extrasynaptic AMPAR pool. Using super-resolution microscopy, we examined how fluorophore size and photostability affected AMPAR trafficking outside of, and within, post-synaptic densities (PSDs) from rats. Organic fluorescent dyes (≈4 nm), quantum dots, either small (≈10 nm diameter; sQDs) or big (>20 nm; bQDs), were coupled to AMPARs via different-sized linkers. We find that >90% of AMPARs labeled with fluorescent dyes or sQDs were diffusing in confined nanodomains in PSDs, which were stable for 15 min or longer. Less than 10% of sQD-AMPARs were extrasynaptic and highly mobile. In contrast, 5–10% of bQD-AMPARs were in PSDs and 90–95% were extrasynaptic as previously observed. Contrary to the hypothesis that AMPAR entry is limited by the occupancy of open PSD ‘slots’, our findings suggest that AMPARs rapidly enter stable ‘nanodomains’ in PSDs with lifetime >15 min, and do not accumulate in extrasynaptic membranes.
Metabolic engineering has facilitated the production of pharmaceuticals, fuels, and soft materials but is generally limited to optimizing well-defined metabolic pathways. We hypothesized that the reaction space available to metabolic engineering could be expanded by coupling extracellular electron transfer to the performance of an exogenous redox-active metal catalyst. Here we demonstrate that the electroactive bacterium can control the activity of a copper catalyst in atom-transfer radical polymerization (ATRP) via extracellular electron transfer. Using, we achieved precise control over the molecular weight and polydispersity of a bioorthogonal polymer while similar organisms, such as , showed no significant activity. We found that catalyst performance was a strong function of bacterial metabolism and specific electron transport proteins, both of which offer potential biological targets for future applications. Overall, our results suggest that manipulating extracellular electron transport pathways may be a general strategy for incorporating organometallic catalysis into the repertoire of metabolically controlled transformations.
Consumption of unsafe water is a major cause of morbidity and mortality in developing regions. Pasteurizing or boiling water to remove pathogens is energy‐intensive and often impractical to off‐grid communities. Therefore, low capital cost, rapid and energy‐efficient water disinfection methods are urgently required to address global challenges of safe water access. Here, anti‐bacterial hydrogels (ABHs) with catechol‐enabled molecular‐level hydrogen peroxide generators and quinone‐anchored activated carbon particles are designed for effective water treatment. The bactericidal effect is attributed to the synergy of hydrogen peroxide and quinone groups to attack essential cell components and disturb bacterial metabolism. ABHs can be directly used as tablets to achieve >99.999% water disinfection efficiency within 60 min without energy input. No harmful byproducts are formed during the treatment process, after which the ABH tablets can be easily removed without residues. Taking advantage of their excellent photothermal and biofouling‐resistant properties, ABHs can also be applied as solar evaporators to achieve stable water purification under sunlight (≤1 kW m−2) after months of storage and operation in bacteria‐containing river water. The ABH platform offers reduced energy and chemical demands for point‐of‐use water treatment technologies in remote areas and emergency rescue applications.
Biological production of inorganic materials is impeded by relatively few organisms possessing genetic and metabolic linkage to material properties. The physiology of electroactive bacteria is intimately tied to inorganic transformations, which makes genetically tractable and well-studied electrogens, such as Shewanella oneidensis, attractive hosts for material synthesis. Notably, this species is capable of reducing a variety of transition-metal ions into functional nanoparticles, but exact mechanisms of nanoparticle biosynthesis remain ill-defined. We report two key factors of extracellular electron transfer by S. oneidensis, the outer membrane cytochrome, MtrC, and soluble redox shuttles (flavins), that affect Pd nanoparticle formation. Changes in the expression and availability of these electron transfer components drastically modulated particle phenotype, including particle synthesis rate, structure, and cellular localization. These relationships may serve as the basis for biologically tailoring Pd nanoparticle catalysts and could potentially be used to direct the biogenesis of other metal nanomaterials.
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