Neutraligands of C5a can potentially occlude the interaction of C5a with the complement receptors C5aR1 and C5aR2

Abstract

The complement system is central to the rapid immune response witnessed in vertebrates and invertebrates, which plays a crucial role in physiology and pathophysiology. Complement activation fuels the proteolytic cascade, which produces several complement fragments that interacts with a distinct set of complement receptors. Among all the complement fragments, C5a is one of

Rational design of antibody‐like peptides for targeting the human complement fragment protein C5a

“…Further, peptides are expected to be less immunogenic and have a lower production cost as compared to antibodies. In this context, major synthetic peptides 13,14 derived from the ECS (NT‐region and ECL2) of the C5aR1 and C5aR2 have confirmed that both the NT‐peptide and ECL2‐peptide of the receptors strongly contribute to the binding of C5a. Further, it is evidenced that the NT‐region of C5aR1 attains an extended sheet‐like structure at the interaction site with C5a.…”

“…The designer antibody‐like peptide fold (Figure 2) based on the poly‐alanine sequence was further subjected to sequence optimization so that it could maintain the desired structural stability in the solution and also effectively bind to neutralize the function of C5a by complementing its overall cationic surface. Moreover, it has been demonstrated that, in addition to the hydrophobic interactions, amino acids with anionic side chains on the NT‐peptide regions 13,14 of C5aR1 and C5aR2 play a significant role in the binding of C5a. Thus, rational sequence optimization of the antibody‐like peptides involved the usage of hydrophobic amino acids as well as amino acids with acidic side chains to aid proper folding of the peptides and to allow the folded peptides to establish intermolecular interactions with C5a through salt bridge, cation‐π, and hydrogen bonding.…”

“…The designer antibody-like peptide fold (Figure 2) based on the polyalanine sequence was further subjected to sequence optimization so that it could maintain the desired structural stability in the solution and also effectively bind to neutralize the function of C5a by complementing its overall cationic surface. Moreover, it has been demonstrated that, in addition to the hydrophobic interactions, amino acids with anionic side chains on the NT-peptide regions 13,14 a significant sequence similarity with other peptides (Figure 3) made of ≤30 aa that have been reported to demonstrate a multi-stranded β-sheet structure. [44][45][46][47] Moreover, the presence of D-chiral amino acids is going to confer proteolytic stability to DePA1 compared to DePA and a combination of the peptide pair can be advantageous in targeting the C5a in biological systems.…”

“…In its receptor‐free form, C5a has been described as a conformationally dynamic protein with a highly flexible L 2 ‐Helix3‐L 3 region and the CT‐region 9 . Both computational 10–12 and experimental 13,14 studies have evidenced that C5a undergoes further conformational changes in response to the binding of the N‐terminal (NT) region of the receptors, which further alters the conformation of the CT‐region of C5a, allowing it to dock into the interhelical crevices of the C5aR1/C5aR2 through conformational selection while establishing intermolecular contacts with the extracellular loop 2 (ECL2) of the receptors 6,7 . In a broad sense, in receptor‐bound form, the bulk and CT‐region of C5a collectively make two‐site contacts with the extracellular surface (ECS) of the receptors (Figure 1) through various electrostatic, hydrogen bonding, and hydrophobic interactions.…”

“…Similarly, L2, Q3, and I6 from the helix 1 region of C5a have also been shown to interact with the ECL2 region of C5aR1 in the cryo-EM-based ternary complex of C5aR1. Notably, E14 and T29 of DePA form strong hydrogen bonds, respectively, with Q3, L2, and M1 of C5a. Similarly, in the ternary complex, K20, Y23, D24, A26, and C27 from the helix 2 region of C5a are also observed to interact with different amino acids of C5aR1.…”