Novel peptide ligands for integrin alpha 6 beta 1 selected from a phage display library

Integrin alpha 6 beta 1 is a major adhesion receptor for the basement membrane, specifically binding to laminin-1. To identify the peptide sequences recognized by alpha 6 beta 1, we screened a 15-mer phage display library by panning with alpha 6 beta 1 purified from human placenta. DNA sequencing of 73 randomly picked phage revealed that three clones were dominantly enriched after repeated panning with alpha 6 beta 1. None of the peptide sequences displayed on these phage showed significant homology to laminin-1. A synthetic peptide modeled after the sequence displayed by one of these phage, designated P3, was found to strongly inhibit the binding of laminin-1 to alpha 6 beta 1. This inhibitory effect of the P3 peptide seems to be specific for alpha 6 beta 1, since it did not affect the binding of fibronectin to integrin alpha 5 beta 1. A synthetic peptide with a scrambled P3 amino acid sequence barely inhibited the binding of laminin-1 to alpha 6 beta 1. When coated on a substratum after conjugation with bovine serum albumin, the P3 peptide was capable of promoting cell spreading in an alpha 6 beta 1-dependent manner, although the peptide with the scrambled sequence showed activity similar to that of a control peptide. These results taken together indicate that the P3 peptide is a novel ligand for integrin alpha 6 beta 1 with potent cell spreading activity.