Bacterial Motility Flashcards
(11 cards)
Types of chemostimuli for E. coli
Attractant: Ser Asp, most sugars
Repellent: Leu, metal ions
Flagella structure
11 protofilaments, inclined, composed of flagellin
Once incorporated, increases a-helical content
Normal, Left-handed, longer waveform 9L-2R
Curly, Right-handed, shorter waveform 8L-3R
Protofilament structure
Each protofilament can be arranged to form either LH or RH superhelical configuration
β-hairpin undergoes an abrupt change in orientation, and the resulting shear may cause alteration of repeat distances between flagellin monomers within a protofilament
RH superhelix form of the protofilament is ~1.5% shorter than the LH-protofilament
Motility of E. coli
Biased random walk
Low reynolds number - sudden stop
Mutagenesis screen
Outer ring - spatial gradient of Ser
Inner ring - spatial gradient of Asp
Types of chemoreceptors
Tsr - serine
Tar - aspartate
MCP clustering and evidence
Forms (clusters) - known as (signalling patches) at poles of the cell - shown by IF and Immuno-gold
Clusters are composed of (signalling teams) - mixed trimers of MCP homodimers, and trimers are inter-linked to form a cluster.
Trimers share a common CheA dimer.
X-ray crystal structure show MCPs assemble as mixed trimers of homodimers
Biochemical studies - enhanced co-operative signalling through CheA
Methylation state can alter stability of complexes
Binding of repellents - immediate response
CheW couples CheA to receptor → CheA-P transautophosphorylation at His → CheY-P at Asp → FliM - CW → Favours tumbling
Binding of repellents - time-dependent adaptation
CheA-P → CheB-P → Rapid demethyl’ of receptor, steady-state establishes
Binding of attractant - immediate response
MCP-CheW, - CheA unphos’, CheY dephos’ by CheZ → Runs
Binding of attractant - time-dependent adaptation
tldr; CheR MCP methylation CheA autophosphorylation Tumbles, steady state establishes
