Characterisation of novel motility proteins in flagellar motors using cryo-electron microscopy
File(s)
Author(s)
Singh, Nanki
Type
Thesis
Abstract
Little is known about the evolution of macromolecular complexes. A prime example of a macromolecular machine is the bacterial flagellar motor. This rotatory molecular motor is embedded in the cell membrane of many bacteria and provides motility. Bacterial flagellar motors have diversified over the course of evolution and vary in structure across different species of bacterium. The core flagellar motor structure remains the same but additional structures have been incorporated into motors which are specific to each species. These structures benefit the bacterium because they act as scaffolds to keep the motor in place or form wider flagellar motors which make more powerful motors that generate high torque and modulate swimming speeds. A flagellar motor that provides high torque benefits bacteria that reside in high viscous environments for example Campylobacter jejuni. The flagellar motor can also ‘sense’ its surrounding environment and signal the bacterium to change its cell morphology as observed in C. crescentus. To power the flagellar motor, transmembrane proteins embedded in the inner membrane rotate against the rotor which generates torque. To understand the evolution of the flagellar motor I first studied these transmembrane proteins using cryo-electron microscopy. I showed significant improvements in the in situ structure of the ring of transmembrane proteins that surround the rotor. I further showed that these transmembrane proteins behave differently in C. jejuni’s high-torque motor compared to low-torque bacteria. To understand the role of the flagellar motor in morphological changes I study two novel proteins known to contribute to this process in C. crescentus using cryo-electron tomography. By studying novel proteins in the flagellar motor of two distinctly diverse species of bacteria C. jejuni and C. crescentus I showed how macromolecular structures have evolved in different species to aid biological function.
Version
Open Access
Date Issued
2024-07-18
Date Awarded
01/02/2025
License URL
Advisor
Beeby, Morgan
Sponsor
Imperial College London
Grant Number
LATPG G98715
Publisher Department
Division of Molecular Biosciences
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)