Crystal structure of a dimerized cockroach allergen Bla g 2 complexed with a monoclonal antibody.
The crystal structure of a 1:1 complex between the German cockroach allergen Bla g 2 and the Fab' fragment of a monoclonal antibody 7C11 was solved at 2.8-angstroms resolution. Bla g 2 binds to the antibody through four loops that include residues 60-70, 83-86, 98-100, and 129-132. Cation-pi interactions exist between Lys-65, Arg-83, and Lys-132 in Bla g 2 and several tyrosines in 7C11. In the complex with Fab', Bla g 2 forms a dimer, which is stabilized by a quasi-four-helix bundle comprised of an alpha-helix and a helical turn from each allergen monomer, exhibiting a novel dimerization mode for an aspartic protease. A disulfide bridge between C51a and C113, unique to the aspartic protease family, connects the two helical elements within each Bla g 2 monomer, thus facilitating formation of the bundle. Mutation of these cysteines, as well as the residues Asn-52, Gln-110, and Ile-114, involved in hydrophobic interactions within the bundle, resulted in a protein that did not dimerize. The mutant proteins induced less beta-hexosaminidase release from mast cells than the wild-type Bla g 2, suggesting a functional role of dimerization in allergenicity. Because 7C11 shares a binding epitope with IgE, the information gained by analysis of the crystal structure of its complex provided guidance for site-directed mutagenesis of the allergen epitope. We have now identified key residues involved in IgE antibody binding; this information will be useful for the design of vaccines for immunotherapy.
Li
Mi
M
Macromolecular Crystallography Laboratory, NCI-Frederick, National Institutes of Health, Frederick, Maryland 21702, USA.
Gustchina
Alla
A
Alexandratos
Jerry
J
Wlodawer
Alexander
A
Wünschmann
Sabina
S
Kepley
Christopher L
CL
Chapman
Martin D
MD
Pomés
Anna
A
D000818:Animals; D000911:Antibodies, Monoclonal; D001120:Arginine; D016282:Aspartic Acid Endopeptidases / Q000737:chemistry* / Q000235:genetics / Q000276:immunology*; D003058:Cockroaches / Q000276:immunology*; D018360:Crystallography, X-Ray; D019281:Dimerization; D006801:Humans; D006967:Hypersensitivity; D019476:Insect Proteins / Q000737:chemistry / Q000276:immunology; D008239:Lysine; D011994:Recombinant Proteins / Q000737:chemistry / Q000276:immunology; D014443:Tyrosine
D000911:Antibodies, Monoclonal; D019476:Insect Proteins; D011994:Recombinant Proteins; D014443:Tyrosine; D001120:Arginine; D016282:Aspartic Acid Endopeptidases; C094699:allergen Bla g 2; D008239:Lysine