The “SNARE” hypothesis

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Presentation transcript:

The “SNARE” hypothesis How do coated vesicles go to the right place and fuse with the right membrane? The “SNARE” hypothesis

SNARE Vesicle-SNAP-receptors (v-SNAREs) Target-SNAP-receptors (t-SNAREs) SNAP=soluble NSF attachment proteins NSF=N-ethylmaleimide-sensitive factor

Lysosomes Digestive enzymes Low pH (4-5) Develop from late endosomes/hydrolases from Golgi Activated by lowering the pH

Extracellular components Cell walls Extracellular matrix Bone Cartilage Connective tissue

Types of molecules in ECM Structural proteins—strength/flexibility Collagen Elastin Proteoglycans--matrix Adhesive glycoproteins—stick cells to matrix Fibronectins laminins

Collagen--strength

Synthesis--fibroblasts

Elastin--flexibility

Glycosaminoglycans

Proteoglycans—hydrated matrix

Adhesive glycoproteins Extracellular Fibronectins Laminins Cell surface Integrins

Fibronectins Group of adhesive glycoproteins 2 long linked proteins Several binding domains

Fibronectin roles Anchor cells to ECM Maintain cell shape Cell movement Blood clotting

Laminins Found in basal laminae Role of basal laminae Contain Special ECM Under epithelial cells Separates them from connective tissue Role of basal laminae Support Permeability barrier Contain Type IV collagen Proteoglycans laminins

Laminins Very large proteins 3 linked peptides Multiple domains

What binds the cells to the ECM?

Integrins Groups of transmembrane proteins Link cytoskeleton to ECM Fibronectin receptor is best known

Cell-cell interactions Cell-cell adhesion Cell-cell communication

Cell-cell adhesion Cell adhesion molecules (CAMs) Cadherins Lots of them Involved in many cellular processes Cadherins Adhesive glycoproteins

Cell juctions Adhesive junctions Tight junctions Gap junctions Strong links Tight junctions Prevent leaks between cells Gap junctions Forms direct link between cells

Adhesive junctions Desmosomes Hemidesmosomes Adherens junctions Focal adhesions All contain - intracellular attachment proteins—link to cytoskeleton - transmembrane linker proteins—link the cells

Desmosomes—rivets between cells

Adherens junctions Belt around cell Connects to actin, not tonofilaments Look a lot like desmosomes Found in Heart Epithelial layers Oftern form belt Called “focal adhesion” if connects to ECM

Tight junctions

Gap junctions Direct electrical connection Formed by connexons Protein=connexin Prominent in muscle and nerve—e.g. electrical tissues Form of cell-cell communication

Cell walls

Plant cell walls Cellulose (40%) Branched polysaccharides Hemicellulose (20%) Pectins (30%) Extensins--glycoproteins (10%) Lignins—woody tissues Insoluble aromatic alcohols Cross-link to form wood

Plasmodesmata

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