Phage display screening of epithelial cell monolayers treated with EGTA: identification of peptide FDFWITP that modulates tight junction activity.

Phage display was used to screen for peptides that modulate the activity of epithelial cell tight junctions. Panning with a phage library that displays random 7-mers was performed using monolayers of human bronchial epithelial cells (16HBE14o(-)) treated with a calcium chelator, ethylene glycol-bis(2-aminoethylether)- N, N, N', N'-tetraacetic acid (EGTA), to increase accessibility to the junctional complex/paracellular space, followed by subtractive panning. A novel peptide, FDFWITP, identified as a potential tight junction modulator, was synthesized in linear and cyclic forms with lysine residues added to improve solubility. The cyclic form of the peptide reduced transepithelial electrical resistance (TER) in a concentration-dependent manner (80% reduction at 100 microM and 95% reduction at 500 microM) and was reversible within 2 h; the linear form only affected TER at the highest concentration. Interestingly, the constrained peptide did not increase permeation of the model small molecule, fluorescein. The highly selective activity of FDFWITP supports the hypothesis that ions and small molecules may be transported paracellularly across tight junctions by separate pathways.

Purification of the Staphylococcus aureus bacteriophages VDX-10 on methacrylate monoliths.

Bacteriophages (phages) are known to be useful in many fields from medicine to agriculture, and for a broad range of applications, including phage therapy and phage display. For some applications, especially in medicine, high purity and viability of phages are required. Methacrylate monoliths (Convective Interaction Media [CIM] monolithic columns), designed for purification of bionanoparticles, were applied for the purification of Staphylococcus aureus phages VDX-10 from bacterial lysate. With a single step purification method, more than 99% of host cell DNA and more than 90% of proteins were removed, with 60% recovery of viable phages. Comparable results were obtained when the purification method was scaled-up from a CIM monolithic disk to a larger CIM monolithic column. Additionally, the dynamic binding capacity of a methacrylate monolith column for S. aureus phages VDX-10 was determined.

The Trp cage motif as a scaffold for the display of a randomized peptide library on bacteriophage T7.

Phage libraries displaying linear or disulfide-constrained peptides often yield weak binders, upon screening against a target, and must be optimized to improve affinity. The disadvantages of libraries based on larger complex proteins, such as single chain antibodies, have stimulated interest in the development of smaller nonimmunoglobulin protein scaffolds. A promising candidate is the Trp cage motif, a 20-residue C-terminal sequence of exendin-4. Amino acid substitution within the Trp cage resulted in a 20-mer peptide recognized as an ultrafast cooperative folding miniprotein, with ideal characteristics for the discovery of small structured nonimmunoglobulin motifs having a stable tertiary structure. Although we were unable to display the Trp cage on M13 phage, successful display was achieved using the lytic T7 phage. Interestingly, mutations were observed at a frequency dependent on display valency. A Trp cage library designed with randomized amino acids at seven solvent-exposed positions was developed from 1.6 x 10(9) primary clones in T7Select10-3b. DNA sequencing of 109 library clones revealed 38% mutants and 16% truncations by TAG codons at randomized positions. Amino acid frequencies were largely within expected bounds and DIVAA analysis revealed that the library had an average diversity of 0.67. Utility of the library was demonstrated by identification of HPQ containing Trp cage miniproteins, which bound streptavidin, and AAADPYAQWLQSMGPHSGRPPPR, which bound to human bronchial epithelial cells. A high complexity library based on the Trp cage miniprotein has demonstrated potential for identifying novel cell and protein binding peptides that could be used for the delivery of therapeutic molecules or as target-specific therapeutic agents.