Unit 5: Cytoskeleton and Cell Motility - Extracellular Matrix and Cell-ECM Interactions

Vocabulary practice flashcards covering the components of the extracellular matrix (ECM) and the primary complexes mediating cell-to-ECM interactions.

Extracellular Matrix (ECM)

A complex network of molecules secreted from cells, but not part of the cell or directly attached to it, that provides structural support and organization to tissues.

Collagen

A fibrous glycoprotein found exclusively in the ECM consisting of a triple helix composed of three helical $\alpha$ chains; it is the most abundant protein in the human body, provides an insoluble framework, and functions as the 'steel beams' of tissue.

Elastin

The primary protein component of elastic fibers that gives the ECM elasticity; it is abundant in glycine and proline, crosslinked via lysine residues, and stretches under tension before relaxing when tension is released.

Proteoglycans

A complex of proteins and polysaccharides consisting of a core protein linked to glycosaminoglycans (GAGs) that attracts water to form a gel, functioning like a sponge to provide cushioning and resist compression.

Glycosaminoglycans (GAGs)

Long polysaccharide chains attached to a core protein in proteoglycans, characterized by a repeating disaccharide structure represented as $\text{-A-B-A-B-}$.

Fibronectins

Extracellular matrix glycoproteins formed by two similar polypeptide subunits joined near their C-termini by disulfide bonds; they act as connectors that bind ECM components and cell surface receptors, directing embryonic cell migration and organ branching.

Fn Domains

A series of approximately $30$ linearly arranged repeating structural domains on fibronectin that contain specific binding sites for other ECM components, blood clotting factors, and cell surface receptors.

RGD Sequence

A specific amino acid sequence found within fibronectin that serves as the binding site recognized by cell surface integrin receptors.

Laminins

A family of at least $15$ cross-shaped extracellular glycoproteins formed by three long polypeptides ($\alpha$, $\beta$, and $\gamma$) held together by disulfide bonds; they strengthen the basement membrane, act like Velcro, and modulate cell migration, growth, and differentiation.

Integrins

Transmembrane cell surface heterodimers composed of an $\alpha$ and a $\beta$ polypeptide subunit that integrate the intracellular cytoskeleton with the extracellular matrix by binding to molecules such as collagen, fibronectin, or laminin.

Integrin $\alpha$ Subunit

The subunit of the integrin heterodimer that primarily dictates ligand-binding specificity for distinct extracellular matrix components.

Focal Adhesions

Specialized cell-ECM attachment sites that allow migratory and non-epithelial cells, such as fibroblasts, to adhere to ECM molecules through clustered integrins linked to bundles of actin filaments.

Talin, Vinculin, and $\alpha$-Actinin

Cytosolic linker proteins that mediate the connection between the cytoplasmic tails of clustered integrins and actin filament bundles within focal adhesions.

Dystrophin Glycoprotein Complex (DGC)

A cell-to-ECM anchoring complex in skeletal and smooth muscle cells that functions like a seatbelt, protecting muscle cells from mechanical stress by linking the intracellular cytoskeleton to basal lamina laminin.

Dystroglycan

A transmembrane glycoprotein within the DGC that provides a structural bridge between extracellular laminin in the basal lamina and intracellular costamere structures.

Costamere

A specialized attachment structure located at the surface of striated muscle cells that contains dystrophin and focal contact proteins, connecting the muscle fiber to the surrounding ECM.

Dystrophin

A spring-like cytoskeletal protein present in costameres that interacts with dystroglycan to anchor intracellular actin filaments to the plasma membrane and ECM.

Hemidesmosomes

Specialized epithelial anchor junctions that function like tent spikes, tethering the basal domain of the cell to the underlying basal lamina via $\alpha_6\beta_4$ integrin in tissues subjected to continuous mechanical strain.

$\alpha_6\beta_4$ Integrin

The specific integrin heterodimer localized within hemidesmosomes that fastens epithelial cells to the underlying basal lamina.

Plectin

A member of the plakin family of linker proteins found in hemidesmosome plaques that links cytoplasmic keratin intermediate filaments to integrins.

BPAG2

A transmembrane hemidesmosomal linker protein (also known as BP180) that, alongside its associated plakin BPAG1 (BP230), connects intermediate keratin filaments to extracellular laminin.