title: Antiferritin VL homodimer binds human spleen ferritin with high specificity.
abstract: The antiferritin variable light domain (VL) dimer binds human spleen ferritin ( approximately 85% L subunits) but with approximately 50-fold lower affinity, K(a)=4 x 10(7) x M(-1), than the parent F11 antibody (K(a)=2.1 x 10(9) x M(-1)). The VL dimer does not recognize either rL (100% L subunits) or rH (100% H subunits) human ferritin, whereas the parent antibody recognizes rL-ferritin. To help explain the differences in ferritin binding affinities and specificities, the crystal structure of the VL domain (2.8A resolution) was determined by molecular replacement and models of the antiferritin VL-VH dimer were made on the basis of antilysozyme antibody D1.3. The domain interface is smaller in the VL dimer but a larger number of interdomain hydrogen bonds may prevent rearrangement on antigen binding. The antigen binding surface of the VL dimer is flatter, lacking a negatively charged pocket found in the VL-VH models, contributed by the CDR3 loop of the VH domain. Loop CDR2 (VL dimer) is located away from the antigen binding site, while the corresponding loop of the VH domain would be located within the antigen binding site. Together these differences lead to 50-fold lower binding affinity in the VL dimer and to more restricted specificity than is seen for the parent antibody.
authors.affiliation: Department of Biochemistry and Pharmacy, Abo Akademi University, P.O. Box 66, FIN-20521, Turku, Finland.
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Nymalm
authors.forename: Zinaida
authors.initials: Z
authors.lastname: Kravchuk
authors.forename: Tiina
authors.initials: T
authors.lastname: Salminen
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Chumanevich
authors.forename: Anatoly P
authors.initials: AP
authors.lastname: Dubnovitsky
authors.forename: Jussi
authors.initials: J
authors.lastname: Kankare
authors.forename: Olli
authors.initials: O
authors.lastname: Pentikäinen
authors.forename: Jukka
authors.initials: J
authors.lastname: Lehtonen
authors.forename: Paolo
authors.initials: P
authors.lastname: Arosio
authors.forename: Sergey
authors.initials: S
authors.lastname: Martsev
authors.forename: Mark S
authors.initials: MS
authors.lastname: Johnson
mesh_terms: D000595:Amino Acid Sequence; D000906:Antibodies / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D018360:Crystallography, X-Ray; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D005293:Ferritins / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D006860:Hydrogen Bonding; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D013154:Spleen / Q000378:metabolism*
chemical_list: D000906:Antibodies; C116856:scF11 antibody; D005293:Ferritins