Chemotaxis and Protein Secretion

Practice flashcards covering bacterial chemotaxis signaling pathways and the various protein secretion systems (Type I-IX) in prokaryotes.

Chemotaxis

The mechanism by which bacteria sense and swim towards attractants and away from repellents.

CCW rotation

Counter-clockwise rotation in peritrichous bacteria that causes flagella to come together into a larger filament for directed movement.

CW rotation

Clockwise rotation in peritrichous bacteria that causes flagella to come apart, resulting in random tumbling movement.

Temporal Gradients

The method by which bacteria sense concentration changes over time rather than spatial gradients due to their small size.

Random Walk

The movement pattern in the absence of a gradient where the frequency of tumbling is random.

Directed movement

A movement state where an increase in $[ ext{attractant}]$ leads to a decrease in the frequency of tumbles and longer runs.

CheA

A histidine kinase that becomes phosphorylated when a Methyl-accepting Chemotaxis Protein (MCP) is not bound to an attractant.

CheW

An adaptor protein that helps the histidine kinase CheA bind to the Methyl-accepting Chemotaxis Protein (MCP).

MCP

Methyl-accepting Chemotaxis Proteins, which act as chemoreceptors and typically cluster near one pole of the cell.

CheY

A response regulator that, when phosphorylated ($CheY ext{~} P$), tells the flagella to tumble.

CheZ

A phosphatase that dephosphorylates $CheY ext{~} P$ to reset the flagellar motor back to its default run state.

Accommodation

A mechanism that allows bacteria to calibrate sensitivity to different $[ ext{attractant}]$ levels to find the highest concentration.

CheR

A methyltransferase that hyper-methylates MCP when a chemoattractant is bound, increasing CheA kinase activity to decrease sensitivity.

CheB

A response regulator and demethylase that, when phosphorylated by $CheA ext{~} P$, demethylates MCP to return it to a previous level of sensitivity.

Tar

An MCP in E. coli that detects the chemoattractants Aspartate and Maltose.

Tsr

An MCP in E. coli that detects the chemoattractant Serine.

Trg

An MCP in E. coli that detects the chemoattractants Galactose and Ribose.

Aer

An MCP in E. coli that detects Oxygen.

Tcp

An MCP found in Salmonella that detects the chemoattractant citrate, replacing Tap.

Tap

An MCP in E. coli that detects Dipeptides but is absent in Salmonella.

Translocation

The transport of proteins from the cytoplasm to the periplasm.

Sec (General Secretion) Pathway

A pathway that transports unfolded preproteins with an amino-terminal signal peptide; it is translocation in Gram-negative cells and secretion in Gram-positive cells.

Tat (Twin Arginine Transporter)

A transporter powered by PMF that actively transports folded proteins and recognizes a highly conserved twin-arginine leader motif $(S/TRRXFLK)$.

Type I Secretion System (T1SS)

A Sec-independent system consisting of an ATP-binding cassette (ABC) transporter and TolC that transports proteins across both membranes using ATP hydrolysis.

Type II Secretion System (T2SS)

A Sec-dependent two-step system that secretes folded proteins (such as Pullulanase of Klebsiella oxytoca) from the periplasm across the outer membrane.

Pseudopilus

A structure in the T2SS that polymerizes to push cargo proteins through a channel in the outer membrane and then depolymerizes to retract.

Type III Secretion System (T3SS)

A Sec-independent contact-dependent system involving 20 or more proteins that can inject virulence proteins directly into a host cell.

Type IV Secretion System (T4SS)

A secretion system used for conjugal transfer of DNA or proteins between bacteria and sometimes to eukaryotic cells.

Type VI Secretion System (T6SS)

A Sec-independent one-step system that uses a phage-related contractile structure to inject effector proteins into target cells.

Type VII Secretion System (T7SS)

Also known as ESX-1, this system is restricted to high-GC-content organisms and Gram-positive bacteria like Mycobacterium.

Type VIII Secretion System (T8SS)

Commonly known as Curli, these systems form scaffolds for adhesive and structural support within biofilms.

Type IX Secretion System (T9SS)

A Sec-dependent system restricted to Bacteroidetes involved in the secretion of effectors like proteases and adhesins.