Enzyme-based protein-tagging systems for site-specific labeling of proteins in living cells

Single and combined toxic effects of nCu and nSiO2 on Dunaliella salina

There are many studies on the toxic effects of single nanoparticles on microalgae; however, many types of nanoparticles are present in the ocean, and more studies on the combined toxic effects of multiple nanoparticles on microalgae are needed. The single and combined toxic effects of nCu and nSiO2 on Dunaliella salina were investigated through changes in instantaneous fluorescence rate (Ft) and antioxidant parameters during 96-h growth inhibition tests. It was found that the toxic effect of nCu on D. salina was greater than that of nSiO2, and both showed time and were dose-dependent with the greatest growth inhibition at 96 h. A total of 0.5 mg/L nCu somewhat promoted the growth of microalgae, but 4.5 and 5.5 mg/L nCu showed negative growth effects on microalgae. The Ft of D. salina was also inhibited by increasing concentrations of nanoparticles and exposure time. nCu suppressed the synthesis of TP and elevated the MDA content of D. salina, which indicated the lipid peroxidation of algal cells. The activities of SOD and CAT showed a trend of increasing and then decreasing with the increase of nCu concentration, suggesting that the enzyme activity first increased and then decreased. The toxic effect of a high concentration of nCu was reduced after the addition of nSiO2. SEM and EDS images showed that nSiO2 could adsorb nCu in seawater. nSiO2 also adsorbed Cu2+ in the cultures, thus reducing the toxic effect of nCu on D. salina to a certain extent. TEM image was used to observe the morphology of algal cells exposed to nCu.

Nanoalbumin-prodrug conjugates prepared via a thiolation-and-conjugation method improve cancer chemotherapy and immune checkpoint blockade therapy by promoting CD8+ T-cell infiltration

Protein-drug conjugates are emerging tools to combat cancers. Here, we adopted an indirect thiolation-and-conjugation method as a general strategy to prepare protein-drug conjugates. We found for the first time that this method led to the formation of nanometric conjugates, probably due to the formation of intermolecular disulfide bonds, which facilitated enhanced uptake by cancer cells. As a proof-of-concept application in cancer therapy, a nanometric albumin-doxorubicin prodrug conjugate (NanoAlb-proDOX) was prepared. The nanometric size promoted its uptake by cancer cells, and the prodrug characteristic defined its selective cytotoxicity toward cancer cells in vitro and reduced side effects in vivo. In multiple tumor xenograft models, nanometric NanoAlb-proDOX showed superior antitumor activity and synergy with immune checkpoint blockade, probably due to the synergistically enhanced tumor CD8⁺ T-cell infiltration and activation. Hence, the thiolation-and-conjugation strategy may serve as a generally applicable method for preparing drug conjugates, and the proof-of-concept nanometric albumin-doxorubicin conjugate may be a good choice for antitumor therapy with the ability to co-stimulate the efficacy of immune checkpoint blockade.

Site-Specific Incorporation of a Photoactivatable Fluorescent Amino Acid

Photoactivatable fluorophores are emerging optical probes for biological applications. Most photoactivatable fluorophores are relatively large in size and need to be activated by ultraviolet light; this dramatically limits their applications. To introduce photoactivatable fluorophores into proteins, recent investigations have explored several protein-labeling technologies, including fluorescein arsenical hairpin (FlAsH) Tag, HaloTag labeling, SNAPTag labeling, and other bioorthogonal chemistry-based methods. However, these technologies require a multistep labeling process. Here, by using genetic code expansion and a single sulfur-for-oxygen atom replacement within an existing fluorescent amino acid, we have site-specifically incorporated the photoactivatable fluorescent amino acid thioacridonylalanine (SAcd) into proteins in a single step. Moreover, upon exposure to visible light, SAcd can be efficiently desulfurized to its oxo derivatives, thus restoring the strong fluorescence of labeled proteins.