A fluorescence assay for detecting amyloid-β using the cytomegalovirus enhancer/promoter

Robust assays for detecting the effects of elevated concentrations of amyloid-β (Aβ) may facilitate Alzheimer’s disease research. An appropriate assay would be high-throughput and enable identification of drugs and genetic mutations that block the effects of Aβ, potentially leading to treatments for Alzheimer’s disease. We discovered that the commonly used cytomegalovirus (CMV) enhancer/promoter is sensitive to the effects of Aβ. By combining the CMV enhancer/promoter with a fluorescent protein, we created a reporter system that produces changes in intracellular fluorescence in response to Aβ. Using hippocampal neurons, we quantified the ability of a CMV-fluorescent protein recombinant reporter to detect both exogenously applied and overexpressed Aβ. This is the first report of a high-throughput enhancer/promoter-based Aβ detection method. The reporter is able to detect the effects of elevated concentrations of Aβ in a high-throughput fashion, providing a new tool for Alzheimer’s disease research and important knowledge about the commonly used CMV enhancer/promoter.

Simultaneous selection and counter-selection for the directed evolution of proteases in E. coli using a cytoplasmic anchoring strategy

With the goal of generating new enzymes that can cleave custom sequences, this article describes a selection strategy for evolving proteases with desirable characteristics. Positive selection and counter-selection are combined to select for and against specified cleavage sequences simultaneously. Cleavage of the positive selection sequence permits E. coli growth, and cleavage of the counter-selection sequence slows growth. Growth occurs when cleavage of the positive selection sequence releases β-lactamase into the periplasm where it can confer antibiotic resistance. The counter-selection traps β-lactamase in the cytoplasm, preventing antibiotic resistance and growth. Thus, proteases with a preference for the positive selection sequence relative to the counter-selection sequence grow more rapidly. This system was used to select a tobacco etch virus (TEV) protease mutant with new substrate compatibility. Biotechnol. Bioeng. 2016;113: 1187-1193. © 2015 Wiley Periodicals, Inc.

N-Terminal labeling of filamentous phage to create cancer marker imaging agents

We report a convenient new technique for the labeling of filamentous phage capsid proteins. Previous reports have shown that phage coat protein residues can be modified, but the lack of chemically distinct amino acids in the coat protein sequences makes it difficult to attach high levels of synthetic molecules without altering the binding capabilities of the phage. To modify the phage with polymer chains, imaging groups, and other molecules, we have developed chemistry to convert the N-terminal amines of the ~4200 coat proteins into ketone groups. These sites can then serve as chemospecific handles for the attachment of alkoxyamine groups through oxime formation. Specifically, we demonstrate the attachment of fluorophores and up to 3000 molecules of 2 kDa poly(ethylene glycol) (PEG2k) to each of the phage capsids without significantly affecting the binding of phage-displayed antibody fragments to EGFR and HER2 (two important epidermal growth factor receptors). We also demonstrate the utility of the modified phage for the characterization of breast cancer cells using multicolor fluorescence microscopy. Due to the widespread use of filamentous phage as display platforms for peptide and protein evolution, we envision that the ability to attach large numbers of synthetic functional groups to their coat proteins will be of significant value to the biological and materials communities.

Viral capsid DNA aptamer conjugates as multivalent cell-targeting vehicles

Nucleic acid aptamers offer significant potential as convenient and evolvable targeting groups for drug delivery. To attach them to the surface of a genome-free viral capsid carrier, an efficient oxidative coupling strategy has been developed. The method involves the periodate-mediated reaction of phenylene diamine substituted oligonucleotides with aniline groups installed on the outer surface of the capsid shells. Up to 60 DNA strands can be attached to each viral capsid with no apparent loss of base-pairing capabilities or protein stability. The ability of the capsids to bind specific cellular targets was demonstrated through the attachment of a 41-nucleotide sequence that targets a tyrosine kinase receptor on Jurkat T cells. After the installation of a fluorescent dye on the capsid interior, capsids bearing the cell-targeting sequence showed significant levels of binding to the cells relative to those of control samples. Colocalization experiments using confocal microscopy indicated that the capsids were endocytosed and trafficked to lysosomes for degradation. These observations suggest that aptamer-labeled capsids could be used for the targeted drug delivery of acid-labile prodrugs that would be preferentially released upon lysosomal acidification.

Oxidative coupling of peptides to a virus capsid containing unnatural amino acids

This Communication describes the chemo- and site-selective coupling of cell type-specific targeting peptides to a virus capsid containing aminophenylalanine residues.