title: An insight into the thermodynamic characteristics of human thrombopoietin complexation with TN1 antibody.
abstract: Human thrombopoietin (hTPO) primarily stimulates megakaryocytopoiesis and platelet production and is neutralized by the mouse TN1 antibody. The thermodynamic characteristics of TN1 antibody-hTPO complexation were analyzed by isothermal titration calorimetry (ITC) using an antigen-binding fragment (Fab) derived from the TN1 antibody (TN1-Fab). To clarify the mechanism by which hTPO is recognized by TN1-Fab the conformation of free TN1-Fab was determined to a resolution of 2.0 Å using X-ray crystallography and compared with the hTPO-bound form of TN1-Fab determined by a previous study. This structural comparison revealed that the conformation of TN1-Fab does not substantially change after hTPO binding and a set of 15 water molecules is released from the antigen-binding site (paratope) of TN1-Fab upon hTPO complexation. Interestingly, the heat capacity change (ΔCp) measured by ITC (-1.52 ± 0.05 kJ mol(-1)  K(-1) ) differed significantly from calculations based upon the X-ray structure data of the hTPO-bound and unbound forms of TN1-Fab (-1.02 ∼ 0.25 kJ mol(-1)  K(-1) ) suggesting that hTPO undergoes an induced-fit conformational change combined with significant desolvation upon TN1-Fab binding. The results shed light on the structural biology associated with neutralizing antibody recognition.
authors.affiliation: Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and Technology, 2-4 Shirakata, Tokai, Ibaraki, 319-1106, Japan. arai.shigeki@qst.go.jp.
authors.forename: Shigeki
authors.initials: S
authors.lastname: Arai
authors.affiliation: Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and Technology, 2-4 Shirakata, Tokai, Ibaraki, 319-1106, Japan.
authors.forename: Chie
authors.initials: C
authors.lastname: Shibazaki
authors.affiliation: Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and Technology, 2-4 Shirakata, Tokai, Ibaraki, 319-1106, Japan.
authors.forename: Motoyasu
authors.initials: M
authors.lastname: Adachi
authors.affiliation: Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and Technology, 2-4 Shirakata, Tokai, Ibaraki, 319-1106, Japan.
authors.forename: Eijiro
authors.initials: E
authors.lastname: Honjo
authors.affiliation: Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and Technology, 2-4 Shirakata, Tokai, Ibaraki, 319-1106, Japan.
authors.forename: Taro
authors.initials: T
authors.lastname: Tamada
authors.affiliation: Kyowa Hakko Kirin Co. Ltd, 3-6-6 Asahi-Cho, Machida, Tokyo, 194-8533, Japan.
authors.forename: Yoshitake
authors.initials: Y
authors.lastname: Maeda
authors.affiliation: Kyowa Hakko Kirin Co. Ltd, 3-6-6 Asahi-Cho, Machida, Tokyo, 194-8533, Japan.
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Tahara
authors.affiliation: Department of Biology, Faculty of Education and Integrated Arts and Sciences, Waseda University, 2-2 Wakamatsu, Shinjuku, Tokyo, 162-8480, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Kato
authors.affiliation: Department of Innovative Drug Discovery and Development, Japan Agency for Medical Research and Development, 1-5-5 Nihonbashi-muromachi, Chuo, Tokyo, 103-0022, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Miyazaki
authors.affiliation: College of Medicine, Florida State University, 1115 West Call Street, Tallahassee, Florida, 32306-4300, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Blaber
authors.affiliation: Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and Technology, 2-4 Shirakata, Tokai, Ibaraki, 319-1106, Japan.
authors.forename: Ryota
authors.initials: R
authors.lastname: Kuroki
mesh_terms: D000818:Animals; D058846:Antibodies, Monoclonal, Murine-Derived / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000737:chemistry*; D051379:Mice; D020836:Protein Structure, Quaternary; D013816:Thermodynamics; D013926:Thrombopoietin / Q000737:chemistry*
chemical_list: D058846:Antibodies, Monoclonal, Murine-Derived; D007140:Immunoglobulin Fab Fragments; D013926:Thrombopoietin
keywords: TN1; X-ray crystallography; antigen-antibody interaction; isothermal titration calorimetry; thrombopoietin