N-Terminal Labeling of Filamentous Phage To Create Cancer Marker Imaging Agents

Department of Chemistry, University of California, Berkeley, California 94720, USA.
ACS Nano (Impact Factor: 12.88). 07/2012; 6(8):6675-80. DOI: 10.1021/nn301134z
Source: PubMed


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.

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    • "There are several advantages of this bacteriophage amplification system: 1) phage clones display sequences identical to specific peptides; 2) phage clones are simple to prepare and purify; 3) phage recombination can produce induced pluripotent stem cells (iPSCs) with intact endogenous gene function13; and 4) phages can tolerate drastic modifications to their coat proteins and serve as a solid support for organic synthesis14. Owing to the specificity, stability, and safety of phages, some groups report that chemically modified or fluorophore-conjugated phages can be used specifically to detect bacteria1516171819 and cancer cells1920. However, using phages to deliver cargo to human ESCs has not been previously reported. "
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