In Silico and In Vitro Studies on the Protein-Protein Interactions between Brugia malayi Immunomodulatory Protein Calreticulin and Human C1q

Abstract

Filarial parasites modulate effective immune response of their host by releasing a variety of immunomodulatory molecules, which help in the long persistence of the parasite within the host. The present study was aimed to characterize an immunomodulatory protein of Brugia malayi and its interaction with the host immune component at the structural and functional level. Our findings showed that Brugia malayi Calreticulin (BmCRT) is responsible for the prevention of classical complement pathway activation via its interaction with the first component C1q of the human host. This was confirmed by inhibition of C1q dependent lysis of immunoglobulin-sensitized Red Blood Cells (S-RBCs). This is possibly the first report which predicts CRT-C1q interaction on the structural content of proteins to explain how BmCRT inhibits this pathway. The molecular docking of BmCRT-C1q complex indicated that C1qB chain (IgG/M and CRP binding sites on C1q) played a major role in the interaction with conserved and non-conserved regions of N and P domain of BmCRT. Out of 37 amino acids of BmCRT involved in the interaction, nine amino acids (Pro126, Glu132, His147, Arg151, His153, Met154, Lys156, Ala196 and Lys212) are absent in human CRT. Both ELISA and in silico analysis showed the significant role of Ca+2 in BmCRT-HuC1q complex formation and deactivation of C1r2–C1s2. Molecular dynamics studies of BmCRT-HuC1q complex showed a deviation from ∼0.4 nm to ∼1.0 nm. CD analyses indicated that BmCRT is composed of 49.6% α helix, 9.6% β sheet and 43.6% random coil. These findings provided valuable information on the architecture and chemistry of BmCRT-C1q interaction and supported the hypothesis that BmCRT binds with huC1q at their targets (IgG/M, CRP) binding sites. This interaction enables the parasite to interfere with the initial stage of host complement activation, which might be helpful in parasites establishment. These results might be utilized for help in blocking the C1q/CRT interaction and preventing parasite infection.

Identification of the complement 9‐binding protein in Setaria equina excretory‐secretory products

“…However, the reduction of C3d indicated the inhibitory action for C3 cleavage and production of C3d . Likewise, the SeqES products of the parasitic nematodes Anisakis simplex , Haemonchus contortus and Brugia malayi could also inhibit the complement activity . In H contortus and B malayi , the C3‐ and C1q‐binding proteins were identified as glyceraldehyde‐3‐phosphate dehydrogenase and calreticulin, respectively.…”

“…Paramyosin was found previously in Trichinella spiralis to bind C1q and C9 and inhibit the formation of membrane attack complex (MAC) . Furthermore, Brugia malayi calreticulin had been found to prevent classical complement pathway activation via its interaction with the first component C1q of the human host …”

D76V, L161R, and C117S are the most pathogenic amino acid substitutions with several dangerous consequences on leptin structure, function, and stability

“…The TM-score is used to evaluate the topological similarity between wild-type and mutant models, while the RMSD measures the average distance between α-carbon backbones of wild-type and mutant models [28]. The greater the RMSD value the greater is the deviation of mutant structure from that of the wild type which in turn changes their functional activity [34]. The mutant model for L161R showed maximum RMSD value which followed by those of D76V and C117S respectively, indicating more alteration forces of L161R compared with the other two D76V and C117S mutation forms ( Table 4).…”

Molecular cloning and characterization of protein disulfide isomerase of Brugia malayi, a human lymphatic filarial parasite

“…Several excretory and secretory (E/S) products are discharged by the parasites as immunomodulatory factors, which are responsible for modulation or blockage of the effective immune response of the host (Allen and Macdonald 1998[ 2 ]; Holland et al, 2000[ 20 ]; Maizels and Yazdanbakhsh, 2003[ 30 ]; Nisbet et al, 2010[ 37 ]). Previously we have reported that calreticulin of filarial parasite differs from host and helps in establishment of infection by modulating the complement system of host (Yadav et al, 2014[ 61 ]). Diethylcarbamazine (DEC), ivermectin alone and in combination with albendazole are mainly microfilaricidal in nature and exert few effects on adult worms.…”