title: Control of domain swapping in bovine odorant-binding protein.
abstract: As revealed by the X-ray structure, bovine odorant-binding protein (OBPb) is a domain swapped dimer [Tegoni, Ramoni, Bignetti, Spinelli and Cambillau (1996) Nat. Struct. Biol. 3, 863-867; Bianchet, Bains, Petosi, Pevsner, Snyder, Monaco and Amzel (1996) Nat. Struct. Biol. 3, 934-939]. This contrasts with all known mammalian OBPs, which are monomers, and in particular with porcine OBP (OBPp), sharing 42.3% identity with OBPb. By the mechanism of domain swapping, monomers are proposed to evolve into dimers and oligomers, as observed in human prion. Comparison of bovine and porcine OBP sequences pointed at OBPp glycine 121, in the hinge linking the beta-barrel to the alpha-helix. The absence of this residue in OBPb might explain why the normal lipocalin beta-turn is not formed. In order to decipher the domain swapping determinants we have produced a mutant of OBPb in which a glycine residue was inserted after position 121, and a mutant of OBPp in which glycine 121 was deleted. The latter mutation did not result in dimerization, while OBPb-121Gly+ became monomeric, suggesting that domain swapping was reversed. Careful structural analysis revealed that besides the presence of a glycine in the hinge, the dimer interface formed by the C-termini and by the presence of the lipocalins conserved disulphide bridge may also control domain swapping.
authors.affiliation: Dipartimento di Produzioni Animali, Biotecnologie Veterinaire, Qualità e Sicurezza degli Alimenti, Università di Parma, Via del Taglio 8, 43100 Parma, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Ramoni
authors.forename: Florence
authors.initials: F
authors.lastname: Vincent
authors.forename: Alison E
authors.initials: AE
authors.lastname: Ashcroft
authors.forename: Paolo
authors.initials: P
authors.lastname: Accornero
authors.forename: Stefano
authors.initials: S
authors.lastname: Grolli
authors.forename: Christel
authors.initials: C
authors.lastname: Valencia
authors.forename: Mariella
authors.initials: M
authors.lastname: Tegoni
authors.forename: Christian
authors.initials: C
authors.lastname: Cambillau
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000873:Anthracenes / Q000378:metabolism; D002417:Cattle; D018360:Crystallography, X-Ray; D019281:Dimerization; D005456:Fluorescent Dyes / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008970:Molecular Weight; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D018035:Receptors, Odorant / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D013552:Swine
chemical_list: D000873:Anthracenes; D005456:Fluorescent Dyes; D020033:Protein Isoforms; D018035:Receptors, Odorant; D011994:Recombinant Proteins; C045648:odorant-binding protein; C049062:1-aminoanthracene