title: Strong in vivo maturation compensates for structurally restricted H3 loops in antibody repertoires.
abstract: A central paradigm in immunology states that successful generation of high affinity antibodies necessitates an immense primary repertoire of antigen-combining sites. Much of the diversity of this repertoire is provided by varying one antigen binding loop, created by inserting randomly a D (diversity) gene out of a small pool between the V and J genes. It is therefore assumed that any particular D-encoded region surrounded by different V and J regions adopts a different conformation. We have solved the structure of two lysozyme-specific variable domains of heavy-chain antibodies isolated from two strictly unrelated dromedaries. These antibodies recombined identical D gene sequences to different V and J precursors with significant variance in their V(D)J junctions. Despite these large differences, the D-encoded loop segments adopt remarkably identical architectures, thus directing the antibodies toward identical epitopes. Furthermore, a striking convergent maturation process occurred in the V region, adapting both binders for their sub-nanomolar affinity association with lysozyme. Hence, on a structural level, humoral immunity may rely more on well developed maturation and selection systems than on the acquisition of large primary repertoires.
authors.affiliation: Laboratory of Cellular and Molecular Immunology, Department of Molecular and Cellular Interactions, Vlaams Interuniversitair Instituut voor Biotechnologie, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium. edegenst@vub.ac.be
authors.forename: Erwin
authors.initials: E
authors.lastname: De Genst
authors.forename: Karen
authors.initials: K
authors.lastname: Silence
authors.forename: Mehdi Arbabi
authors.initials: MA
authors.lastname: Ghahroudi
authors.forename: Klaas
authors.initials: K
authors.lastname: Decanniere
authors.forename: Remy
authors.initials: R
authors.lastname: Loris
authors.forename: Jörg
authors.initials: J
authors.lastname: Kinne
authors.forename: Lode
authors.initials: L
authors.lastname: Wyns
authors.forename: Serge
authors.initials: S
authors.lastname: Muyldermans
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000917:Antibody Formation / Q000502:physiology; D000941:Antigens / Q000737:chemistry / Q000378:metabolism; D001483:Base Sequence; D001666:Binding Sites, Antibody / Q000235:genetics; D002162:Camelus / Q000276:immunology; D005803:Genes, Immunoglobulin; D007143:Immunoglobulin Heavy Chains / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D007135:Immunoglobulin Variable Region / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes; D009113:Muramidase / Q000276:immunology; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment
chemical_list: D000941:Antigens; D007143:Immunoglobulin Heavy Chains; D007135:Immunoglobulin Variable Region; D046912:Multiprotein Complexes; D009113:Muramidase