Lysine‐50 is a likely site for anchoring the plasminogen N‐terminal peptide to lysine‐binding kringles

Interactions between the kringle 4 (K4) domain of human plasminogen (Pgn) and segments of the N‐terminal Glul‐Lys77 peptide (NTP) have been investigated via 1H‐NMR at 500 MHz. NTP peptide stretches devoid of Lys residues but carrying an internal Arg residue show negligible affinity toward K4 (equilibrium association constant Ka < 0.05 mM−1). In contrast, while most fragments containing an internal Lys residue exhibit affinities comparable to that shown by the blocked Lys derivative Nα‐acetyl‐L‐lysine‐methyl ester (Ka ˜ 0.2 mM−1), peptides encompassing Lys50 consistently show higher Ka values. Among the investigated linear peptides, Nα‐acetyl‐Ala‐Phe‐Tyr‐His‐Ser‐Ser‐Lys50‐Glu‐Gln‐NH2 (AcAFYHSKSOEQ‐NH2) exhibits the strongest interaction with K4 (Ka ˜ 1.4 mM−1), followed by AcYHSKSOEQ‐NH2 (Ka ˜ 0.9 mM−1). Relative to the wild‐type sequence, mutated hexapeptides exhibit lesser affinity for K4. When a Lys50 → Ser mutation was introduced (⇒ AcYHSSSOEQ‐NH2), binding was abolished.