Estructura y funcionamiento de los flagelos

How Do Bacterial Flagella Function?

Structure and Components of Bacterial Flagella

• Many species of bacteria propel themselves using helical motorized flagella, with different structures: rotator cells have one flagellum each, while E. coli has multiple flagella that rotate in bundles.

• Each flagellum consists of three main parts: a helical filament, a flexible rotating hook, and the basal body located beneath the cell surface.

• The basal body is composed of a rod and several rings embedded in the inner membrane, peptidoglycan layer, and outer membrane; some rings form the flagellar motor.

Mechanism of Rotation

• The motor can be divided into two parts: the stator (attached to the peptidoglycan layer and stationary) and the rotor (which rotates).

• The rotor's power derives from a proton gradient across the membrane; protons flow through proteins MoA and MoB in the stator, suggesting that an aspartic acid residue in MoB plays a role in proton conductance.

Power Stroke Dynamics

• Although not fully understood, one model proposes that protons bind to aspartic acids in MoB proteins causing conformational changes that result in incremental movement of the rotor during power strokes.

• After releasing protons into the cytoplasm at each stroke, further conformational changes drive subsequent power strokes engaging the rotor again.

Assembly Process of Flagella

• Flagellar assembly begins with integral membrane protein subunits called FleF forming an MS ring; FleG proteins assemble under this ring along with other proteins to create the rotor.

• In Gram-negative bacteria like E. coli, additional rings (L and P rings) penetrate the outer membrane to support rod assembly; once exposed outside, these components are replaced by hook caps guiding further assembly.

Final Assembly Steps