Structure of a bacterial cell surface decaheme electron conduit

Area of Science:

• Microbiology
• Biochemistry
• Structural Biology

Background:

• Bacteria like Shewanella oneidensis use extracellular minerals as respiratory electron acceptors.
• This process involves decaheme cytochromes on the bacterial cell surface, part of trans-outer-membrane electron transfer pathways.
• These cytochromes may mediate electron transfer to insoluble minerals, flavin electron shuttles, or other cytochromes via nanowires.

Purpose of the Study:

• To determine the 3.2-Å crystal structure of the decaheme cytochrome MtrF from Shewanella oneidensis.
• To visualize the spatial organization of the 10 hemes within the MtrF protein.
• To gain molecular insights into MtrF's potential roles in diverse extracellular electron transfer processes.

Main Methods:

• X-ray crystallography was used to obtain the 3.2-Å structure of MtrF.
• Analysis of the crystal structure to determine the arrangement and conformation of the 10 hemes.
• Structural interpretation to understand potential electron transfer mechanisms.

Main Results:

• The crystal structure of MtrF reveals a unique crossed conformation of its 10 hemes across four domains.
• A staggered 65-Å octaheme chain runs the protein's length, bisected by a planar 45-Å tetraheme chain.
• The tetraheme chain connects two extended Greek key split β-barrel domains.

Conclusions:

• The MtrF structure provides the first visualization of decaheme arrangement in these key bacterial electron transfer proteins.
• The unique heme organization suggests a trifurcated electron transport chain capable of simultaneously interacting with insoluble minerals, soluble flavins, and other cytochromes.
• This structural insight explains how MtrF facilitates versatile extracellular respiration in Shewanella oneidensis.