The Interaction Between Recombinant Protein F Derived from Nontypeable Haemophilus influenzae and Lipoprotein(a)

摘要

Protein F (PF) is a surface plasminogen (Plg) receptor on the nontypeable Haemophilus influenzae (NTHi). Plg via its lysine binding sites (LBS) can bind to PF. Apolipoprotein(a) [Apo(a)] is one component of Lipoprotein(a) [Lp(a)]. It has Kringle (K) domains, which contain LBS and has a high homology with Plg. Therefore, we speculated that Lp(a) might bind to Plg receptor on the surface of NTHi, subsequently competitively inhibiting the interaction of NTHi with Plg. In this study, recombinant PF (rPF) and its C-terminal lysine residue-deleted variant (rPFΔK) were expressed in E. coli BL21. The interactions of rPF with Plg and Lp(a) were tested by ELISA. The results showed that rPF could bind to Plg and Lp(a). The binding capacity of rPF was significantly higher than that of rPFΔK. The interactions of rPF with Plg and Lp(a) could be inhibited by EACA. 2 mmol/L of EACA significantly inhibited the binding of rPF to Plg, while 0.2 mmol/L of EACA could significantly reduce the binding of rPF to Lp(a). 50 ng/100 μL Lp(a) could significantly inhibit the interaction of rPF with Plg. In addition, affinity chromatography assay 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 Plg and Lp(a) should be responsible for these specifically bindings. Lp(a) could combine with rPF consequently inhibiting the interaction of Plg with rPF. This revealed that Lp(a) might play a role in anti-NTHi infection.