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Bacterial Flagella

Updated: Nov 24, 2022

Writer: Dicle Dilan Yardimci

Many bacteria use helical motorized flagella to move across their environment. Ecoli cells contain many flagella that revolve in bundles, whereas rotor bacteria cells have only one flagellum. Each flagellum is made up of a helical filament that spins at a rate of 100 times per second and is 20 nanometers broad and up to 15 microns long. Speculative models and schema ties for how bacterial flagella might function and assemble. The filament is attached to a flexible revolving hook just outside the cell wall. The flagellum is made up of three parts: a filament, a hook, and a component termed the basal body that lies beneath the cell surface. A rod and a sequence of rings embedded in the inner membrane, peptidoglycan layer, and outer membrane make up the basal body.

The flagellar motor is made up of several rings and is separated into two parts: the stator, which is connected to the peptidoglycan layer and remains fixed, and the rotor, which rotates. The motor is powered by a proton gradient that runs across the membrane. Outside the cell, there is a large concentration of protons, whereas inside the cell, there is a low concentration. The protons travel across the stator's interface, which is made up of two types of proteins named MotA and MotB. According to mutational research, a conserved aspartic acid in MotB is involved in proton conductance. Two MotB proteins are found in each stator.

As a result, it contains two of these crucial aspartic acids. Although the molecular mechanism of rotation is unknown, one proposed model depicts protons traveling through stators' channels and attaching to aspartic acid in MotB proteins. Because of this interaction, MotA proteins undergo a conformational shift, resulting in the first power stroke, which incrementally drives the rotor. Two protons were released into the cytoplasm at the end of the first power stroke. The loss of a proton results in a second conformational change, which generates the second power stroke. Engaging the rotor once again.

Many features of flagellar assembly have been discovered, despite the fact that the mechanism for motor function is still unknown. Flagella are made up of structures that start in the inner membrane. The MS ring is made up of 26 subunits of an integral membrane called FliF that join together in the plasma membrane. Under the MS ring, the FliG proteins assemble. The rotor is made composed of the proteins FliG, FliM, and FliN. Flagellar proteins destined for the extracellular section of the flagellum are exported from a cell and assembled at the center via a flagellum-specific export route. The stator of the flagellar motor was made up of MotA and MotB, which were the stationary parts. Both are membrane proteins, but MotB is attached to the hard peptidoglycan layer, which helps to maintain the stator proteins in place.

The rod component of the rotor's subunits go up through the hollow cylinder in the assembly and, with the help of cap proteins, build up the road from proximal to distal. Gram-negative bacteria, such as E. coli, have a different set of rings termed L & P rings. They pass through the outer membrane and form a bearing for the rod. When the rod cap is exposed outside the L ring, it dissociates and is replaced by a hook cap, which guides the hook proteins' assembly. The hook cap dissociates after the hook is assembled, and a sequence of junction proteins form between the hook and future filaments. Finally, a new cap is constructed, and filament proteins assemble similarly to rod and hook proteins, traveling through the hollow channel inside the filament to the distal end.

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