As a target for selection, we employed hepatitis C virus protease (HCVp) NS3a. Globular protein NS3a that binds to helical peptide inhibitors; small molecules like grazoprevir are known to compete with this class of helical peptides. This distinctive characteristic makes NS3a an attractive target for peptide ligand discovery, allowing the use of potent small molecule inhibitors to displace peptide binders at specific binding sites. To test this hypothesis, we conducted a selection campaign starting from previously published 10 9 linear X15 peptides displayed on phage, using inactive, non-membrane interactive NS3a variant NS3aH1 58 in NS3a buffer (20 mM Tris, 300 mM NaCl, pH 8.0, 1 mM DTT) as a bait. Elution by grazoprevir was used as a driving force for the selection (Figure ). From the panning results, we observed robust selection indicators: 240,000-fold inflection of phage recovery in round 3 compared to round 2; 850-fold stronger enrichment towards NS3aH1 than blank streptavidin beads control; a prominent motif, HXDMT observed in 1608 out of 3000 peptides that passed Differential Enrichment (DE) analysis of Next Generation Sequencing (NGS). The same motif was present in 34 out of 50 most abundantly observed peptides in Round 3 (Figure , Supplementary Table ). Furthermore, BLI assay confirmed that a HXDMT containing synthetic peptide TQMYYHEDMTLNYQR exhibited binding to NS3aH1 with Kd = 51.6 nM (Figure ), and the binding was inhibited by grazoprevir (Figure ). Given the promising results, we proceeded with NS3aH1 as a selection target and grazoprevir as an elution agent for more indepth exploration of the late-stage reshaping of phage libraries.