title: Characterization of C69R variant HBsAg: effect on binding to anti-HBs and the structure of virus-like particles.
abstract: Several variants of the major "a" determinant of the HBsAg, the main target of HBV neutralization by antibodies, have been described. However, mutations outside this region have not been as thoroughly investigated. During the genotyping of HBV from Tunisian patients with chronic hepatitis B, we identified a variant with a C69R substitution in the cytosolic loop of the S protein, resulting in a change in the hydrophobicity profile compared to the wild-type HBsAg. Wild-type and mutant HBsAgs were produced in Saccharomyces cerevisiae and recombinant proteins were tested for their ability to correctly self-assemble into virus-like particles (VLPs), and their ability to bind to HBs antibodies. The C69R substitution resulted in a decrease in binding to commercial anti-HBs antibodies, and although the variant appeared to assemble properly into VLPs, the average size of the particles was larger than that of the wild-type HBsAg. Prediction of the tertiary structure of the C69R mutant revealed a change in the first (aa 60-70) and the second loop (aa 110 to 120) compared to the wild-type protein. Furthermore, we showed by an isothermal titration calorimetry assay that the interaction between the wild-type HBsAg and the anti-HBs antibody was exothermic, whereas that with the mutant C69R was endothermic, indicating an effect on the binding affinity.
authors.affiliation: Laboratory of "Biomass Valorisation and Production of Eukaryotic Proteins", Center of Biotechnology of Sfax, University of Sfax, Route Sidi Mansour, BPK 1177, 3018, Sfax, Tunisia.
authors.forename: Nadia
authors.initials: N
authors.lastname: Hadiji-Abbes
authors.affiliation: Laboratory of "Biomass Valorisation and Production of Eukaryotic Proteins", Center of Biotechnology of Sfax, University of Sfax, Route Sidi Mansour, BPK 1177, 3018, Sfax, Tunisia.
authors.forename: Wafa
authors.initials: W
authors.lastname: Mihoubi
authors.affiliation: Laboratory Charles Coulomb UMR 5221, University of Montpellier, Place Eugène Bataillon, CC074, 34095, Montpellier Cedex 5, France.
authors.forename: Marta
authors.initials: M
authors.lastname: Martin
authors.affiliation: Laboratory "Polymères, Biopolymères, Surfaces" UMR 6270, University of Rouen, Bd Maurice de Broglie, 76821, Mont Saint Aignan Cedex, France.
authors.forename: Carole
authors.initials: C
authors.lastname: Karakasyan-Dia
authors.affiliation: Faculty of Sciences, University of Sfax, Sfax, Tunisia.
authors.forename: Fakher
authors.initials: F
authors.lastname: Frikha
authors.affiliation: Laboratory Charles Coulomb UMR 5221, University of Montpellier, Place Eugène Bataillon, CC074, 34095, Montpellier Cedex 5, France.
authors.forename: Csilla
authors.initials: C
authors.lastname: Gergely
authors.affiliation: Laboratory "Polymères, Biopolymères, Surfaces" UMR 6270, University of Rouen, Bd Maurice de Broglie, 76821, Mont Saint Aignan Cedex, France.
authors.forename: Thierry
authors.initials: T
authors.lastname: Jouenne
authors.affiliation: Laboratory of "Biomass Valorisation and Production of Eukaryotic Proteins", Center of Biotechnology of Sfax, University of Sfax, Route Sidi Mansour, BPK 1177, 3018, Sfax, Tunisia.
authors.forename: Ali
authors.initials: A
authors.lastname: Gargouri
authors.affiliation: Laboratory of "Biomass Valorisation and Production of Eukaryotic Proteins", Center of Biotechnology of Sfax, University of Sfax, Route Sidi Mansour, BPK 1177, 3018, Sfax, Tunisia. raja.gargouri@cbs.rnrt.tn.
authors.forename: Raja
authors.initials: R
authors.lastname: Mokdad-Gargouri
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D005838:Genotype; D006509:Hepatitis B / Q000821:virology*; D006510:Hepatitis B Antibodies / Q000378:metabolism*; D006514:Hepatitis B Surface Antigens / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D006515:Hepatitis B virus / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data
chemical_list: D006510:Hepatitis B Antibodies; D006514:Hepatitis B Surface Antigens