title: Structural consequences of mutations in interfacial Tyr residues of a protein antigen-antibody complex. The case of HyHEL-10-HEL.
abstract: Tyrosine is an important amino acid in protein-protein interaction hot spots. In particular, many Tyr residues are located in the antigen-binding sites of antibodies and endow high affinity and high specificity to these antibodies. To investigate the role of interfacial Tyr residues in protein-protein interactions, we performed crystallographic studies and thermodynamic analyses of the interaction between hen egg lysozyme (HEL) and the anti-HEL antibody HyHEL-10 Fv fragment. HyHEL-10 has six Tyr residues in its antigen-binding site, which were systematically mutated to Phe and Ala using site-directed mutagenesis. The crystal structures revealed several critical roles for these Tyr residues in the interaction between HEL and HyHEL-10 as follows: 1) the aromatic ring of Tyr-50 in the light chain (LTyr-50) was important for the correct ternary structure of variable regions of the immunoglobulin light chain and heavy chain and of HEL; 2) deletion of the hydroxyl group of Tyr-50 in the heavy chain (HTyr-50) resulted in structural changes in the antigen-antibody interface; and 3) the side chains of HTyr-33 and HTyr-53 may help induce fitting of the antibody to the antigen. Hot spot Tyr residues may contribute to the high affinity and high specificity of the antigen-antibody interaction through a diverse set of structural and thermodynamic interactions.
authors.affiliation: Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Aoba-yama 6-6-11, Sendai 980-8579, Japan.
authors.forename: Mitsunori
authors.initials: M
authors.lastname: Shiroishi
authors.forename: Kouhei
authors.initials: K
authors.lastname: Tsumoto
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Tanaka
authors.forename: Akiko
authors.initials: A
authors.lastname: Yokota
authors.forename: Takeshi
authors.initials: T
authors.lastname: Nakanishi
authors.forename: Hidemasa
authors.initials: H
authors.lastname: Kondo
authors.forename: Izumi
authors.initials: I
authors.lastname: Kumagai
mesh_terms: D000818:Animals; D000936:Antigen-Antibody Complex / Q000737:chemistry* / Q000235:genetics; D002645:Chickens; D018360:Crystallography, X-Ray; D004527:Egg Proteins; D007128:Immunoglobulin Fragments / Q000737:chemistry*; D009113:Muramidase / Q000737:chemistry* / Q000235:genetics / Q000276:immunology*; D009154:Mutation; D011487:Protein Conformation; D013816:Thermodynamics; D014443:Tyrosine
chemical_list: D000936:Antigen-Antibody Complex; D004527:Egg Proteins; D007128:Immunoglobulin Fragments; C055966:immunoglobulin Fv; D014443:Tyrosine; D009113:Muramidase