Cryo-electron tomography of periplasmic flagella in Borrelia burgdorferi reveals a distinct cytoplasmic ATPase complex.

Zhuan Qin,Md A Motaleb,Tao Lin,Steven J Norris,Jun Liu,Chunhao Li,Jiagang Tu

doi:10.1371/journal.pbio.3000050

Zhuan Qin, Md A Motaleb + Show 5 more

Open Access

https://doi.org/10.1371/journal.pbio.3000050

Copy DOI

Abstract

Periplasmic flagella are essential for the distinct morphology and motility of spirochetes. A flagella-specific type III secretion system (fT3SS) composed of a membrane-bound export apparatus and a cytosolic ATPase complex is responsible for the assembly of the periplasmic flagella. Here, we deployed cryo-electron tomography (cryo-ET) to visualize the fT3SS machine in the Lyme disease spirochete Borrelia burgdorferi. We show, for the first time, that the cytosolic ATPase complex is attached to the flagellar C-ring through multiple spokes to form the “spoke and hub” structure in B. burgdorferi. This structure not only strengthens structural rigidity of the round-shaped C-ring but also appears to rotate with the C-ring. Our studies provide structural insights into the unique mechanisms underlying assembly and rotation of the periplasmic flagella and may provide the basis for the development of novel therapeutic strategies against several pathogenic spirochetes.

Highlights

A group of bacteria named spirochetes can cause serious human diseases such as Lyme disease (Borrelia or Borreliella species), syphilis (Treponema pallidum subsp. pallidum), and leptospirosis (Leptospira interrogans and other Leptospira species)
By analyzing 7,242 intact motor structures extracted from tomographic data collected on a direct detection device (DDD), we generated an asymmetric reconstruction that revealed the previously observed 16-fold symmetry of the collar and stator structures [10,11,39] and disclosed a novel spoke-like structure underneath the C- and MS-rings (S1 Fig and S1 Movie)
The overall organization of the flagella-specific type III secretion system (fT3SS) machine in the B. burgdorferi periplasmic flagella shares many similar features observed with the fT3SS machine in the E. coli external flagella [50] and the virulence T3SS (vT3SS) machines in Shigella and Salmonella [40,43,44] (Fig 4)

Summary

Introduction

A group of bacteria named spirochetes can cause serious human diseases such as Lyme disease (Borrelia or Borreliella species), syphilis (Treponema pallidum subsp. pallidum), and leptospirosis (Leptospira interrogans and other Leptospira species). Similar to the flagella in the model organisms Escherichia coli and Salmonella enterica, periplasmic flagella are composed of the flagellar motor, the hook, and the filament. A periplasmic “collar” contributes significantly to the motor structures observed in B. burgdorferi [10,11] and all other spirochetes characterized to date [12,13,14,15]. Spirochetes have unusual flagellar hooks in which the hook proteins are cross-linked by a covalent bond, which is required to transmit the torque from the motor to the filament [17]. Those spirochete-specific features enable the spirochetes to bore through viscous environments in their animal hosts

Methods

Results

Conclusion