Structural study of ExbB-ExbD-TonB that is responsible for energy transduction of proton motive force in bacteria

2017 Fiscal Year Final Research Report

• Project/Area Number: 15K06986
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Structural biochemistry
• Research Institution: Institute of Physical and Chemical Research
• Principal Investigator: Maki-Yonekura Saori 国立研究開発法人理化学研究所, 放射光科学総合研究センター, 研究員 (20513386)
• Co-Investigator(Kenkyū-buntansha): 米倉 功治 国立研究開発法人理化学研究所, 放射光科学総合研究センター, 主任研究員 (50346144)
• Project Period (FY): 2015-04-01 – 2018-03-31
• Keywords: X線結晶構造解析 / クライオ電子顕微鏡 / イオンチャネル / プロトン駆動力

Outline of Final Research Achievements

Gram-negative bacteria import essential nutrients such as iron and vitamin B12 through outer membrane receptors. This process utilizes proton motive force harvested by the Ton system made up of three inner membrane proteins, ExbB, ExbD and TonB. ExbB and ExbD form the proton channel that energizes uptake through TonB.
We report the structures of hexameric complexes of ExbB and ExbD revealed by X-ray crystallography and single particle cryo-EM. Image analysis shows that hexameric and pentameric complexes coexist, with the proportion of hexamer increasing with pH. Channel current measurement and 2D crystallography support the existence and transition of the two oligomeric states in membranes. The hexameric complex consists of six ExbB subunits and three ExbD transmembrane helices enclosed within the central channel. We propose models for activation/inactivation associated with hexamer and pentamer formation and utilization of proton motive force.

Free Research Field

生物物理