AN M-13-PHAGE LIBRARY DISPLAYING RANDOM 38-AMINO-ACID PEPTIDES AS A SOURCE OF NOVEL SEQUENCES WITH AFFINITY TO SELECTED TARGETS

We have examined the potential of isolating novel ligands from a libra ry of M 1 3 pIII-fusion phage displaying peptides composed of 38 rando m amino acids (aa). The library was panned with streptavidin (SA) and a polyclonal goat anti-mouse IgG Fc antibody (Ab) preparation coupled to paramagnetic beads. SA selected two classes of phage from the libra ry. One class exhibited the aa motif, HP(Q/M)THETA (where THETA signif ies a non-polar aa), similar to the motif identified by Devlin et al. [Science 249 (1990) 404-406] using a 15-aa random peptide library disp layed on phage. The other class of phage had no discernible motif In b inding experiments, the non-HP(Q/M)THETA phage had a slightly higher a ffinity for SA than did the motif phage. Both classes of SA-binding ph age failed to bind native and non-glycosylated forms of avidin, even t hough SA and avidin are structurally similar and both proteins possess extraordinary affinities for biotin. The polyclonal goat anti-mouse I gG Fc Ab preparation selected phage displaying sequences similar to a region of the mouse IgG Fc. Thus, a single immunodominant epitope on t he mouse IgG Fc was identified. Furthermore, a second phage displaying peptides with no discernible sequence similarities to mouse IgG Fc wa s isolated. Thus, an M13 library displaying 38-aa peptides can yield p hage with affinity for various targets. Finally, we have observed a bi ological bias against odd numbers of Cys residues in the displayed pep tides.