(A) Plot of affinities (relative association constants, Kas) of the Nt-Ile–bearing peptide IGLWKS for GID4116–300 and its indicated single-residue mutants, with the affinity of wild-type GID4116–300 for IGLWKS taken as 100%. NDB, no detectable binding (Kd > 0.5 mM). (B) Plot of affinities (relative association constants, Kas) of the Nt-Ile–bearing peptide IGLWKS for GID4116–300 and its indicated position-173 mutants, with the affinity of wild-type GID4116–300 for IGLWKS taken as 100%. (C) Plot of affinities (relative association constants, Kas) of the Nt-Pro–bearing peptide PGLWKS for GID4116–300 and its indicated position-173 mutants, with the affinity of wild-type GID4116–300 for PGLWKS taken as 100%. In B and C, the highest-affinity levels for position-173 GID4 mutants (they differ for the IGLWKS versus PGLWKS peptides) are highlighted in red.