The stringency of selection was increased by decreasing the amount of immobilized protein, decreasing the incubation time with DevR protein, and increasing the percentage of Tween-20

in the washing buffer in each successive round (Table 1). The loosely bound phages were discarded by elution with DevR D54N mutant protein (100 μg mL−1 concentration), which differs from the wild-type protein at the phosphorylation site (Saini et al., 2004). A second elution was performed with buffer containing 250 mM imidazole that released the His6-tagged protein along with the tightly bound phages. Three rounds of panning were performed using the twin elutions approach, and each time the phages in the imidazole elution were amplified and used as an input for the next round of panning. The fourth and fifth rounds were performed on plate to eliminate bead binders (Table 1). The loosely bound phages

were first eluted with mutant D54N DevR protein and FK228 then with 0.2 M glycine, pH 2.2. In the fifth (final) round of panning, a penultimate elution using phosphorylated DevS was carried out prior to final elution of the bound phages using 0.2 M glycine. Phage titers in the elution used as an input for the next round of panning were determined according to manufacturer’s instructions. D54Na, 250 mM imidazole D54N, 250 mM imidazole D54N, 250 mM imidazole D54N, 0.2 M glycine D54N, DevS~P, 0.2 M glycine ELISA was PTC124 performed to screen for high-affinity binder phages. Briefly, individual phage plaques from the DevS~P and glycine elutions from the final round of panning were amplified, and the culture supernatants (containing phages) were screened by ELISA for binding to (His)6-DevR or BSA or to Metabolism inhibitor plastic. Briefly, plates were coated overnight with 10 μg per well protein or

left uncoated. After blocking overnight with BSA (5 mg mL−1), the plates were washed thrice with TBS (50 mM Tris–HCl, pH 7.5, and 150 mM NaCl). This was followed by incubation with phage supernatants for 1 h and subsequent vigorous washing with 0.5% Tween-20 in TBS (TBST). The bound phages were detected with horseradish peroxidase (HRP)-conjugated anti-M13 antibody (Amersham Biosciences, UK) using o-phenylenediamine as a substrate, and A490 was measured. The extent of binding to DevR was calculated (A490 nm in DevR-coated wells − A490 nm in control wells). For competition experiments, 1011 phages were added to DevR-coated wells (10 μg per well) in the presence of increasing amounts of synthetic peptide and allowed to compete for 1 h, and the bound phages were detected with HRP-conjugated anti-M13 antibody. The DNA of high-affinity binder phages was sequenced to determine peptide-coding phage sequences. A single peptide sequence ‘TLHLHHL’ was repeated 15 times of 19 clones sequenced. A peptide having this sequence was synthesized (Techno Concept Pvt. Ltd., New Delhi, India) and named as DevRS1.