The Interaction Of Lipoprotein(a) With Protein F Derived From Nontypeable Haemophilus Influenzae

Protein F (PF) is a plasminogen (Plg) receptor on the surface of nontypeable Haemophilus influenzae (NTHi). Pig via its lysine binding sites (LBS) binds to PF. Apolipoprotein (a) [Apo(a)] is one component of lipoprotein(a) [lipoprotein(a), Lp(a)]. It shares a high homology with Pig and its Kringle (K) domains, especially the KIV10 domain contains a high affinity LBS. Therefore, we speculated that Lp(a) might bind to PF on the surface of NTHi, subsequently competitively inhibited the interaction of PF with Pig.In this study, the interactions of recombinant Protein F (rPF) and its C-terminal lysine residue-deleted variant (rPF△K) with plasminogen (Pig) and lipoprotein(a) [Lp(a)] were investigated.Firstly, rPF and rPFAK were expressed in E. coli BL21 and purified by affinity resin. Secondly, the interactions of rPF and rPF△K with Pig and Lp(a) were tested by ELISA. The results showed that rPF could bind to Pig and Lp(a). The binding capacity of rPF was significantly higher than that of rPFAK. The inhibition assay indicated that:1) the interactions of rPF with Pig and Lp(a) could be inhibited by EACA.2 mmol/L of EACA significantly inhibited the binding of rPF to Pig, while 0.2 mmol/L of EACA could significantly reduce the binding of rPF to Lp(a).2) 50 ng/100μL of Lp(a) could significantly inhibit the interaction of rPF with Pig. Moreover, affinity chromatography followed by Western biotting was also used to study the interaction. In overall, C-terminal lysine residue of rPF and the lysine binding sites (LBS) of Lp(a) should be responsible for the binding. Lp(a) could combine with rPF consequently inhibiting the interaction of Plg with rPF. This implied that Lp(a) might play an important role in anti-NTHi infection.