title: Crystal structure of a dominant B-cell epitope from the preS2 region of hepatitis B virus in the form of an inserted peptide segment in maltodextrin-binding protein.
abstract: We report here the crystal structure of MalE-B363, a recombinant construction of maltodextrin-binding protein bearing a dominant B-cell epitope sequence from the preS2 region of the hepatitis B surface antigen. The inserted peptide sequence, which replaces the seven carboxy-terminal residues of maltodextrin-binding protein, carries the 14 amino acid residue epitope contained between residues 132 and 145 from the preS2 region. The epitope sequence is flanked on either side by additional residues that result from the genetically engineered insertion, bringing the total length of the foreign peptide to 26 amino acid residues. The hybrid protein has been previously shown to be recognised by monoclonal antibodies elicited by the native viral antigen. Three independent molecules of MalE-B363 are present in the asymmetric unit of the crystal. All 14 epitope residues could be traced for one molecule, ten epitope residues had significant electron density for the second, but no density was visible for the epitope of the third. The conformation of the amino-terminal segment of the epitope from Gln132(e) to Gly138(e) is similar in the two molecules of MalE-B363 for which the foreign peptide could be traced. Moreover, the conformation of a smaller segment, comprising residues Asp133(e) to Arg137(e), is similar to that present in the previously determined crystal structure of MalE-B133, another insertion/deletion mutant of maltodextrin-binding protein bearing the preS2 epitope. The presence of a common structural motif for the same sequence in disparate molecular environments suggests that this conformation might be present also in the native viral antigen. This could provide a structural basis to explain the cross-reactivity of anti-preS2 monoclonal antibodies with these hybrid proteins.
authors.affiliation: C.N.R.S. U.R.A. 1961, Institut Pasteur, 25 rue du Dr. Roux, Paris cedex 15, 75724, France.
authors.forename: F A
authors.initials: FA
authors.lastname: Saul
authors.forename: B
authors.initials: B
authors.lastname: Vulliez-le Normand
authors.forename: F
authors.initials: F
authors.lastname: Lema
authors.forename: G A
authors.initials: GA
authors.lastname: Bentley
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry*; D002352:Carrier Proteins / Q000737:chemistry*; D003461:Crystallography; D000939:Epitopes / Q000737:chemistry*; D029968:Escherichia coli Proteins; D006514:Hepatitis B Surface Antigens / Q000737:chemistry* / Q000276:immunology; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry*; D033902:Periplasmic Binding Proteins; D011487:Protein Conformation; D011498:Protein Precursors / Q000737:chemistry* / Q000276:immunology; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D014759:Viral Envelope Proteins / Q000737:chemistry* / Q000276:immunology
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D000939:Epitopes; D029968:Escherichia coli Proteins; D006514:Hepatitis B Surface Antigens; C461619:MalE protein, E coli; D010455:Peptides; D033902:Periplasmic Binding Proteins; D011498:Protein Precursors; D011993:Recombinant Fusion Proteins; D014759:Viral Envelope Proteins; C050807:presurface protein 2, hepatitis B surface antigen