Atypical chemoreceptor arrays accommodate high membrane curvature

Area of Science:

• Microbiology
• Cellular Biology
• Structural Biology

Background:

• The prokaryotic chemotaxis system is a well-established signaling pathway crucial for bacterial motility and environmental sensing.
• Chemoreceptors in known systems typically form hexagonal (P6 symmetry) arrays, organizing the signaling machinery.
• High membrane curvature presents a challenge for the assembly of large protein arrays.

Purpose of the Study:

• To investigate the structural organization of the chemotaxis apparatus in Treponema denticola, a bacterium with highly curved membranes.
• To determine the symmetry and molecular arrangement of chemoreceptor arrays in T. denticola.
• To identify novel components or organizational principles within this prokaryotic signaling system.

Main Methods:

• Cryo-electron tomography (cryo-ET) was employed to visualize the native structure of the chemotaxis arrays.
• Analysis of protein organization, including the histidine kinase CheA, CheW, and CheR-like fusion proteins.
• Investigation of the role of the oxygen sensor ODP in array assembly.

Main Results:

• Identified a novel P2 symmetry in the T. denticola chemotaxis apparatus, distinct from the canonical P6 symmetry.
• Revealed a linear organization of the histidine kinase CheA, contributing to the P2 symmetry and accommodating high membrane curvature.
• Discovered atypical features including an extended CheA dimerization domain and a CheW-CheR-like fusion protein essential for array order.
• Demonstrated that the oxygen sensor ODP influences the ordering of CheA within the arrays.

Conclusions:

• The chemotaxis system in Treponema denticola exhibits a unique P2 symmetry, adapted for highly curved membranes.
• This discovery highlights a greater diversity in the structural organization and assembly of prokaryotic chemotaxis signaling arrays than previously recognized.
• The findings suggest novel evolutionary strategies for chemosensory systems in bacteria with distinct cellular morphologies.