Monomeric Covalent-Avidin for Rapid and Covalent Labeling of Quantum Dots to Cell Surface Proteins

Quantum Dot Imaging Agents: Haematopoietic Cell Interactions and Biocompatibility

Quantum dots (QDs) are semi-conducting nanoparticles that have been developed for a range of biological and non-biological functions. They can be tuned to multiple different emission wavelengths and can have significant benefits over other fluorescent systems. Many studies have utilised QDs with a cadmium-based core; however, these QDs have since been shown to have poor biological compatibility. Therefore, other QDs, such as indium phosphide QDs, have been developed. These QDs retain excellent fluorescent intensity and tunability but are thought to have elevated biological compatibility. Herein we discuss the applicability of a range of QDs to the cardiovascular system. Key disease states such as myocardial infarction and stroke are associated with cardiovascular disease (CVD), and there is an opportunity to improve clinical imaging to aide clinical outcomes for these disease states. QDs offer potential clinical benefits given their ability to perform multiple functions, such as carry an imaging agent, a therapy, and a targeting motif. Two key cell types associated with CVD are platelets and immune cells. Both cell types play key roles in establishing an inflammatory environment within CVD, and as such aid the formation of pathological thrombi. However, it is unclear at present how and with which cell types QDs interact, and if they potentially drive unwanted changes or activation of these cell types. Therefore, although QDs show great promise for boosting imaging capability, further work needs to be completed to fully understand their biological compatibility.

Compact and modular bioprobe: Integrating SpyCatcher/SpyTag recombinant proteins with zwitterionic polymer-coated quantum dots

The development of quantum dot (QD)-based modular bioprobe that has a compact size and enable a facile conjugation of various biofunctional groups is in high demand. To address this, we surface engineered QDs with zwitterion polymer ligands to have an inherent compact size and derivatized them sequentially with the recombinant proteins SpyCatcher/SpyTag (SC/ST) to use their protein ligation system. SC/ST spontaneously form one complex through the isopeptide bond between them. SC-conjugated QDs (QD-SC) were used as base building blocks. Then, ST-biomolecules were added for modular biofunctionalization. We synthesized compact sized (∼15 nm) QD-SC-ST-affibody (antibody-mimicking small protein for tumor detection) conjugates, which showed successful cell-receptor targeting. The target cell-receptor could be easily tuned by changing the type of ST-affibody. We also demonstrated that anti-human-chorionic-gonadotropin mouse IgG1 antibodies can be labeled on the QD surface by mixing QD-SC with the ST-MG1Nb (mouse-IgG1-specific protein). The immunoassay performance of the antibody-labeled QDs was evaluated using a pregnancy test kit, displaying equivalent detection sensitivity to a commercially available kit. This study proposed an innovative strategy for QD biofunctionalization in a modular manner, which can be expanded to a diverse range of colloidal particle derivatization.

A Dual-Metal-Catalyzed Sequential Cascade Reaction in an Engineered Protein Cage

Herein, we describe the creation of an artificial protein cage housing a dual-metal-tagged guest protein that catalyzes a linear, two-step sequential cascade reaction. The guest protein consists of a fusion protein of HaloTag and monomeric rhizavidin. Inside the protein capsid, we established a ruthenium-catalyzed allylcarbamate deprotection reaction followed by a gold-catalyzed ring-closing hydroamination reaction that led to indoles and phenanthridines with an overall yield of up to 66 % in aqueous solutions. Furthermore, we show that the encapsulation stabilizes the metal catalysts against deactivation by air, proteins and cell lysate.

An efficient cell type specific conjugating method for incorporating various nanostructures to genetically encoded AviTag expressed optogenetic opsins

Here, we report genetically encoded AviTag conjugating system for Channelrhodopsin-2(ChR2) in order to attach various nanostructures to the membrane protein in a cell type specific manner. First, AviTag peptide sequence is cloned to N-terminal site of ChR2 construct and expressed at the membrane of primary-cultured hippocampal neurons via lentiviral transduction. Second, with the help of BirA enzyme and ATP, biotin coated quantum dots (Qdots) and streptavidin (SAv) coated Qdots are successfully bound to AviTag sites at the membrane where ChR2 is located and confirmed by fluorescence imaging. Moreover, we synthesize biotinylated Traptavidin-DNA conjugate probes containing a desthio-biotin that has weaker affinity than a regular biotin, and successfully exchange them with pre-conjugated Biotin-AviTag-ChR2 site at the membrane of neuronal cells which can potentially solve the crosslinking issue of Avidin linked probes. Therefore, we expect the AviTag-ChR2 fusion platform to become a great tool for incorporating various nanostructures at the specific sites of a cellular membrane in order to overcome the limits of optogenetic opsins.