Structural study of the microglia/macrophage-specific protein Iba1 from human and mouse having an actin-binding activity

• Project/Area Number: 18570109
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Structural biochemistry
• Research Institution: Kagawa University
• Principal Investigator: KAMITORI Shigehiro Kagawa University, Life Science Research Center, Professor (00262246)
• Co-Investigator(Kenkyū-buntansha): YOSHIDA Hiromi Kagawa University, Life Science Research Center, Associate Professor (10313305)
• Project Period (FY): 2006 – 2007
• Project Status: Completed (Fiscal Year 2007)
• Budget Amount: ¥3,890,000 (Direct Cost: ¥3,500,000、Indirect Cost: ¥390,000); Fiscal Year 2007: ¥1,690,000 (Direct Cost: ¥1,300,000、Indirect Cost: ¥390,000); Fiscal Year 2006: ¥2,200,000 (Direct Cost: ¥2,200,000)
• Keywords: X-ray structure / Calcium binding protein / EF-hand protein / Microglia / Actin-binding protein / Conformational change / Protein Complex / Synchrotron radiation

Research Abstract

Iba1 (ionized calcium-binding adaptor molecule 1) with 147 amino acid residues has been identified as a calcium (Ca^<2+>)-binding protein, expressed specifically in microglia/macrophages, and is expected to be a key factor in membrane ruffling which is a typical feature of activated microglia. We have determined the crystal structure of human Iba1 in Ca^<2+> free form and mouse Iba1 in Ca^<2+> -bound form, to a resolution of 1.9 A and 2.1 A, respectively. X-ray structures of Iba1 revealed a compact, single-domain protein with two EF-hand motifs, showing similarity in overall topology to partial structures of the classical EF-hand proteins troponin C and calmodulin. In mouse Iba1, the second EF-hand contains a bound Ca^<2+>, but the first EF-hand does not, which is often the case in S100 proteins, suggesting that Iba1 has S100 protein-like EF-hands. However, the molecular conformational change induced by Ca^<2+>-binding of Iba1 is different from that found in the classical EF-hand proteins and/or S100 proteins, leading to the formation of a dimer in a crystal, which demonstrates that Iba1 has an unique molecular switching mechanism dependent on Ca^<2+>-binding. The dimer has the shape of a slightly flat quadratic prism with the characteristic charge distribution; negatively charged regions are widely distributed on the upper surface and sides, while the unusual positively charged region is found at the center of the lower surface. It is likely that this positively charged region interacts with a target molecule. To elucidate the oligomeric state of Iba1 in a solution, cross-linking experiments was done, showing that Iba1 partially forms a dimer in a solution. To investigate whether a dimer Iba1 can interacts with target molecules or not, we also done surface plasmon resonance studies, but a clear evidence for this has not yet been obtained.

Research Products

• [Journal Article] X-ray structures ofthe microglia/macrophage-specific protein Iba1 from human and mouse demonstrate novel molecular confomation change induced by calcium-binding (2006)
  • Author(s): Yamada, M., Ohsawa, K., Imai, Y., Kohsaka, S. & Kamitori, S.
  • Journal Title: J. Mol. Biol. 364 Pages: 449-457
  • Description: 「研究成果報告書概要(和文)」より
  • Peer Reviewed
• [Journal Article] X-ray structures of the microglia/macrophage-specific protein IBal from human and mouse demonstrate novel molecular conformation change induced by calcium-binding (2006)
  • Author(s): Yamada, M., Ohsawa, K., Imai, Y., Kohsaka, S., Kamitori, S
  • Journal Title: J. Mol. Biol. 364 Pages: 449-457
  • Description: 「研究成果報告書概要(欧文)」より
• [Journal Article] X-ray structures of the microglia/macrophage-specific protein Ibal from human and mouse demonstrate novel molecular conformation change induced by calcium-binding. (2006)
  • Author(s): Yamada, M., Ohsawa, K., Imai, Y., Kohsaka, S., Kamitori, S.
  • Journal Title: J.Mol.Biol. 364 Pages: 449-457
• [Presentation] Binding modes of microglia-specific EF-hand protein Iba1 with targets deduced from X-ray structures (2007)
  • Author(s): Yamada, M., Yoshida, H., Ohsawa, K., Imai, Y., Kohsaka, S. & Kamitori, S.
  • Organizer: 32nd FEBS Congress
  • Place of Presentation: Vienna, Austria
  • Year and Date: 2007-07-10
  • Description: 「研究成果報告書概要(和文)」より
• [Presentation] Binding modes of microglia-specific EF-hand protein Ibal with targets deduced from X-ray structures (2007)
  • Author(s): Yamada, M., Yoshida, H., Ohsawa, K., Imai, Y., Kohsaka, S., Kamitori, S
  • Organizer: 32nd FEBS Congress
  • Place of Presentation: Vienna, Austria
  • Description: 「研究成果報告書概要(欧文)」より
• [Presentation] Binding modes of microglia-specific EF-hand protein Ibal with targets deduced from X-ray structures (2007)
  • Author(s): Yamada M.., Yoshida, H.., Ohsawa K., Imai, Y., Kohsaka, S.and Kamitori S.
  • Organizer: 32nd FEBS Congress
  • Place of Presentation: Vienna,Austria
• [Presentation] Binding modes of microglia-specific EF-hand protein Ibal with targets deduced from X-ray structures (2006)
  • Author(s): Yamada, M., Yoshida, H., Ohsawa, K., Imai, Y., Kohsaka, S., Kamitori, S
  • Organizer: 20th IUBMB International Congress of Biochemistry and Molecular Biology
  • Place of Presentation: Kyoto, Japan
  • Year and Date: 2006-07-23
  • Description: 「研究成果報告書概要(欧文)」より
• [Presentation] X-ray structure of microglia/macrophage-specific protein Iba1 and its binding study to actin and L-fimbin (2006)
  • Author(s): Yamada, M., Yoshida, H., Imai, Y., Ohasawa, K, Kohsaka, S. & Kamitori, S.
  • Organizer: 20th IUBMB International Congress of Biochemistry and Molecular Biology
  • Place of Presentation: Kyoto, Japan
  • Year and Date: 2006-06-23
  • Description: 「研究成果報告書概要(和文)」より
• [Remarks] 「研究成果報告書概要(和文)」より
  • URL: http://www.med.kagawa-u.ac.jp/~xraylab/
• [Remarks]
  • URL: http://www.med.kagawa-u.ac.jp/~xraylab/