The extracellular matrix and glycoconjugates

What is the ECM?

A gel-like network of polysaccharides, proteoglycans, and proteins found just outside the plasma membrane.

What is the role of ECM?

Holds cells together, provides strength and elasticity, allows diffusion of oxygen/nutrients, serves as a recognition site, and acts as a barrier (e.g., to tumor cells).

What are glycosaminoglycans (GAGs)?

Long, linear heteropolysaccharides made of repeating disaccharide units, found in the ECM.

What are the roles of GAGs?

Form sticky meshworks with fibrous proteins, support connective tissue, lubricate joints, and anchor ECM to cells.

What are GAGs made of?

One sugar is either N-acetylglucosamine or N-acetylgalactosamine, sometimes sulfated.

What are glycoconjugates?

Molecules where carbohydrates are covalently linked to proteins or lipids.

What is the role of glycoconjugates?

Information carriers:

• Communication between cells

• Recognition sites for signal molecules

• Label proteins for transport or degradation

What happens when tumor cells secrete heparinase?

They degrade the ECM to invade surrounding tissues.

What is hyaluronan (hyaluronic acid)?

A non-sulfated GAG not linked to protein; gives strength and elasticity to cartilage, lubricates joints, and fills the eye’s vitreous humor.

What is chondroitin sulfate?

A GAG that gives tensile strength to cartilage, tendons, ligaments, and aorta walls; usually attached to proteins.

What is keratan sulfate?

A GAG found in the cornea, cartilage, bones, and in structures like hooves and claws; protein-attached.

Heparin

A highly sulfated, negatively charged linear GAG that prevents blood clotting by activating antithrombin.

Heparan sulfate

Similar to heparin but attached to proteins; regulates development and blood vessel formation.

What else can heparin bind to?

Viruses and bacteria—can reduce virulence, but some viruses exploit it to invade cells.

proteoglycan?

A core protein with long, negatively charged GAG chains; the polysaccharide portion dominates by weight.

Where are proteoglycans found?

In all extracellular matrices (ECMs); often function as structural and signaling components.

What is a glycoprotein?

A protein with small oligosaccharides attached via its anomeric carbon.

What are the roles of glycoproteins?

Protein-protein recognition, especially in antibodies; some are used to create vaccines.

How are oligosaccharides attached in glycoproteins?

N-linked (via asparagine) or O-linked (via serine/threonine).

mucins?

Glycoproteins with many O-linked oligosaccharides, important in lubrication and protective barriers.

glycolipid?

A lipid molecule with covalently attached oligosaccharides.

Where are glycolipids found?

In cell membranes; help determine blood groups in vertebrates and are involved in immune recognition.

What are bacterial lipopolysaccharides?

Glycolipids on Gram-negative bacteria that can trigger immune responses; Lipid A portion is an endotoxin.

: How do cells interact with the ECM?

Through membrane proteins like syndecans (proteoglycans) and integrins (receptors for ECM).

What functions do integrins perform?

Link the ECM to the cytoskeleton and transmit signals that control growth, mobility, apoptosis, and wound healing.