Cytoskeleton, Actin, and Listeria Infection

Flashcards covering key vocabulary related to the cytoskeleton, actin dynamics, and Listeria infection based on the provided lecture notes.

Cytoskeleton

An intracellular network of protein filaments and tubules that provides structural support, facilitates cell motility, and resists mechanical stresses.

Microfilaments (Actin Filaments)

The smallest cytoskeletal elements, about 8 nanometers in diameter, composed of polymerized G-actin monomers, also known as actin filaments.

Microtubules

The largest cytoskeletal elements, about 25 nanometers in diameter, composed of 13 protofilaments forming water-filled tubes polarized with plus and minus ends.

Intermediate Filaments

Cytoskeletal elements intermediate in size, non-polarized, and play a crucial role in cellular strength and resisting mechanical forces.

Septins

A type of cytoskeleton element briefly mentioned, distinct from microfilaments, microtubules, and intermediate filaments.

Immunofluorescence

A visualization technique using fluorescent antibodies to detect individual cytoskeletal elements in cells due to the historical difficulty of traditional light microscopy.

G-Actin

Monomeric actin, a single polypeptide chain that binds ATP and possesses ATP hydrolytic activity, polymerizing to form F-actin.

Plus End (Actin)

Also called the barbed end, it is the rapidly growing end of an actin filament where G-actin monomers add quickly.

Minus End (Actin)

Also called the pointed end, it is the slowly growing or disassembling end of an actin filament.

ATP Hydrolytic Activity (Actin)

The spontaneous hydrolysis of bound ATP to ADP by G-actin monomers once incorporated into an actin filament, which reduces monomer affinity for each other.

Nucleation (Actin Polymerization)

The rate-limiting step in actin polymerization, involving the slow formation of an oligomer (typically three G-actins).

Elongation (Actin Polymerization)

The rapid growth of an actin filament after nucleation, as monomers quickly add to the polymer.

Critical Concentration (Actin)

The concentration of G-actin monomers at which the rate of monomer addition to the polymer equals the rate of monomer dissociation, indicating no net polymerization.

Actin Treadmilling

A phenomenon where at a specific monomer concentration, there is net addition at the plus end and net removal at the minus end, with no net change in filament length, resulting in monomers moving through the filament.

Lamellipodium

A broad, sheet-like protrusion at the leading edge of a migrating cell, driven by actin polymerization and the formation of dendritic networks.

Microvilli

Non-motile, finger-like extensions of the apical plasma membrane, supported by parallel actin bundles, that increase the surface area for nutrient absorption.

Terminal Web (Microvilli)

A network of actin filaments at the base of microvilli, anchored to adhering junctions near the apical end of cells.

Stress Fibers

Contractile bundles of actin filaments, often arranged antiparallel and crosslinked by alpha-actinin, which resist or apply tension across a cell.

Cell Cortex

The region immediately beneath (deep to) the plasma membrane in most cells, rich in actin filaments, which plays a key role in regulating cell shape and extensions.

Rho Family GTPases

Monomeric G proteins (like CDC42, RAC, RHO) that bind GTP in their active state and GDP in their inactive state, important for regulating the actin cytoskeleton.

CDC42

A Rho family GTPase whose activation typically induces the formation of filopodia.

RAC

A Rho family GTPase whose activation typically induces the formation of lamellipodia.

RHO

A Rho family GTPase whose activation typically induces the formation of stress fibers and focal adhesions.

Chemotaxis

The directional movement of a cell (e.g., a neutrophil) in response to a chemical gradient, driven by orchestrated actin dynamics at the leading and trailing edges.

Professional Phagocytes

Cells such as neutrophils and macrophages that are specialized in chasing down and engulfing pathogens (e.g., bacteria) via phagocytosis.

Profilin

An actin-binding protein that binds to G-actin, encouraging its polymerization by leaving the plus-end interacting face available and increasing its affinity for the plus end.

Thymosin

An actin-binding protein that binds stoichiometrically to G-actin, preventing it from polymerizing by blocking the region required for plus-end addition.

ARP2/3 Complex

A multi-subunit actin-related protein complex that nucleates actin filament formation, stabilizes the minus end, mediates side-filament attachment, and forms dendritic webs.

Dendritic Web

A tree-like network of actin filaments formed by the ARP2/3 complex, often characterized by 70-degree branch angles between filaments.

Formins

A family of actin-associated proteins that form dimeric functional complexes at the plus end of actin filaments to encourage monomer association and filament growth.

Fimbrin

An actin crosslinking protein that creates tight parallel bundles of actin filaments, as seen in microvilli, supporting structure without motility.

Alpha-Actinin

An actin crosslinking protein that arranges microfilaments in antiparallel arrays with sufficient spacing for myosin motors, prominent in stress fibers.

Filamin

An actin crosslinking protein that functions as a dimer with long, flexible arms, allowing it to form flexible, three-dimensional gel-like networks of actin filaments.

Gelsolin

A well-known severing protein that cuts actin filaments, modulating their length and stability.

Tropomyosin

An actin-stabilizing protein that binds along the side of actin filaments, important in regulating their structure and interactions.

Trunculin

An actin inhibitor, a sponge molecule that depolymerizes actin by binding and sequestering G-actin subunits.

Cytochalasin B

An actin inhibitor that promotes depolymerization by blocking the plus end of actin filaments, preventing monomer addition.

Phalloidin

A toxin from the death cap mushroom that stabilizes actin filaments by binding along their side, preventing depolymerization and disrupting normal cell function.

Listeria

A bacterium responsible for food poisoning that hijacks the ARP2/3 complex using its ActA protein to build an actin tail, enabling intracellular motility and cell-to-cell spread.

ActA (Listeria)

A cell surface protein of Listeria that specifically recruits and activates the host cell's ARP2/3 complex to initiate actin polymerization, forming an 'actin tail'.

Actin Tail (Listeria)

A comet-shaped structure of actin microfilaments generated by Listeria via ActA and ARP2/3 complex, which propels the bacterium through the host cell cytoplasm and facilitates cell-to-cell transmission.

Cell-to-Cell Transmission (Listeria)

The process by which Listeria uses the force generated by its actin tail to propel itself from an infected cell directly into an adjacent host cell, avoiding the extracellular environment.

Autophagy Escape (Listeria)

A mechanism where Listeria's actin network formation may allow it to break through pre-autophagosomal structures, preventing its clearance by the host cell's autophagy pathway.