Download L 11Flagellar motors

FLAGELLAR MOTORS
Objectives
• Functions of bacterial flagella.
• How flagellar motors work to bring about
locomotion!!!
Bacteria Swim by Rotating Their
Flagella
• Bacteria
swim
by
rotating flagella that
protrude from their
surfaces.
• When the flagella rotate
in a counter clockwise
direction, the separate
flagella form a bundle
that very efficiently
propels the bacterium
through solution.
Bacterial flagella in a bundle
Bacterial flagella
• Bacterial flagella are polymers approximately 15 nm in
diameter and as much as 15 μm in length, composed of a
protein called flagellin.
• Each flagellum has a hollow core.
• At its base, each flagellum has
a rotory motor (200-1000rpm).
• Three parts: Basal body, hook
and filament
Deriving forces of flageller motion
• ATP is not used for flagellar motion.
• The necessary free energy is derived from either the
proton gradient or sodium ion gradient that exists
across the plasma membrane.
• Hence, either proton motive force or sodium motive
force facilitates flagellar motion.
• Flagella do not rotate at a constant speed but
instead can increase or decrease their rotational
speed in relation to the strength of the proton
motive force.
Proton motive force
• The bacterial flagellum is driven by a rotary engine.
The engine is powered by proton motive force, i.e., by
the flow of protons (hydrogen ions) across the
bacterial cell membrane due to a concentration
gradient set up by the cell's metabolism
Sodium motive force
• In some bacteria especially marine bacteria,
ion channels eject sodium ions from the cell.
This leads to formation of sodium ion
gradient. This gradient can also be used as
intermediate
energy
storage
for
flagellar rotation.
• This gradient is a form of sodium motive force
which assists in flagellar rotation.
Flagellar Motor
• Five components crucial to motor function have
been identified.
• MotA and MotB are membrane proteins.
• Approximately 11 MotA - MotB pairs form a ring
around the base of the flagellum.
• The proteins FliG, FliM, and FliN are part of a disclike structure called the MS (membrane and
supramembrane) ring, with approximately 30 FliG
subunits coming together to form the ring.
Flagellar Motion
• The MotA - MotB pair and FliG combine to create a
proton channel that drives rotation of the flagellum.
• Each MotA - MotB pair is conjectured to form a
structure that has two half-channels; FliG serves as
the rotating proton carrier
• A proton from the periplasmic space passes into the
outer half channel and is transferred to an FliG
subunit.
• The MS ring rotates, rotating the flagellum with it
and allowing the proton to pass into the inner halfchannel and into the cell.
Flagellar Motion
Flagella
Sensory Role of Flagella:
Bacterial Chemotaxis
• In the presence of a gradient of certain substances
such as glucose, bacteria swim preferentially toward
the direction of the higher concentration of the
substance. Such compounds are referred to as
chemoattractants (positive chemotaxis).
• Bacteria also swim preferentially away from
potentially harmful compounds such as phenol, a
chemorepellant (negative chemotaxis).
• The process of moving in specific directions in
response to environmental cues is called chemotaxis.
Bacterial Chemotaxis
• The bacteria swim in one
direction for some length of
time, senses the concentration
of
chemo-attractants
or
chemo-repellants , tumble
briefly, and then set off in a
new direction.
• Tumbling is caused by an
abrupt reversal of the flagellar
motor, which disperses the
flagellar bundle for some time.
Flagella changing direction