title: 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 (Pro(126), Glu(132), His(147), Arg(151), His(153), Met(154), Lys(156), Ala(196) and Lys(212)) 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.
authors.affiliation: Division of Biochemistry, CSIR-Central Drug Research Institute, BS10/1, Sector 10, Jankipuram extension, Lucknow, Uttar Pradesh, India.
authors.forename: Sunita
authors.initials: S
authors.lastname: Yadav
authors.affiliation: Division of Biochemistry, CSIR-Central Drug Research Institute, BS10/1, Sector 10, Jankipuram extension, Lucknow, Uttar Pradesh, India.
authors.forename: Smita
authors.initials: S
authors.lastname: Gupta
authors.affiliation: Computer Aided Drug Design and Molecular Modeling Lab, Department of Bioinformatics, Alagappa University, Karaikudi, Tamilnadu, India.
authors.forename: Chandrabose
authors.initials: C
authors.lastname: Selvaraj
authors.affiliation: Division of Biochemistry, CSIR-Central Drug Research Institute, BS10/1, Sector 10, Jankipuram extension, Lucknow, Uttar Pradesh, India.
authors.forename: Pawan Kumar
authors.initials: PK
authors.lastname: Doharey
authors.affiliation: Division of Biochemistry, CSIR-Central Drug Research Institute, BS10/1, Sector 10, Jankipuram extension, Lucknow, Uttar Pradesh, India.
authors.forename: Anita
authors.initials: A
authors.lastname: Verma
authors.affiliation: Computer Aided Drug Design and Molecular Modeling Lab, Department of Bioinformatics, Alagappa University, Karaikudi, Tamilnadu, India.
authors.forename: Sanjeev Kumar
authors.initials: SK
authors.lastname: Singh
authors.affiliation: Division of Biochemistry, CSIR-Central Drug Research Institute, BS10/1, Sector 10, Jankipuram extension, Lucknow, Uttar Pradesh, India.
authors.forename: Jitendra Kumar
authors.initials: JK
authors.lastname: Saxena
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000276:immunology; D017178:Brugia malayi / Q000737:chemistry* / Q000276:immunology / Q000472:pathogenicity; D037282:Calreticulin / Q000737:chemistry* / Q000276:immunology; D015922:Complement C1q / Q000235:genetics* / Q000276:immunology; D003171:Complement Pathway, Classical / Q000235:genetics / Q000276:immunology; D018360:Crystallography, X-Ray; D054884:Host-Pathogen Interactions / Q000235:genetics / Q000276:immunology*; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology; D056747:Immunomodulation; D011485:Protein Binding; D060066:Protein Interaction Maps / Q000235:genetics / Q000276:immunology; D017433:Protein Structure, Secondary
chemical_list: D037282:Calreticulin; D007074:Immunoglobulin G; D015922:Complement C1q