BSCI 1510 Vesicular Transport I Lecture

Vesicle Transport Overview

  • Vesicle transport involves mechanism for moving materials within cells, particularly between membrane-bound compartments.

  • Key cellular structures involved:

    • Nucleus

    • Endoplasmic Reticulum (ER)

    • Golgi Apparatus

    • Mitochondria

    • Lysosomes

    • Endosomes

    • Peroxisomes

Big Questions in Vesicle Transport

  • What is the basic mechanism of vesicle transport?

  • What different types of protein coats are involved in vesicle budding?

    • COP II: ER —> Golgi

    • COP I: Golgi —> ER (retrograde transport)

    • Clathrin: Golgi or plasma membrane to endosomes or lysosomes

  • What is the structure and function of the Golgi apparatus?

  • How do proteins pass through the Golgi?

  • What proteins are involved in membrane fusion?

Mechanism of Vesicular Transport

  • Vesicles bud from donor compartments carrying transport cargo. These vesicles then fuse with acceptor compartments.

  • Process includes:

    • Vesicle budding: Driven by coat proteins (COPs)

    • Transport: Utilizes microtubules and motor proteins.

    • Vesicle fusion: Involves tethers and SNARE proteins.

Types of Coated Vesicles

  • Types of Coated Vesicles include:

    • Clathrin-coated vesicles: Transport from the Golgi apparatus to lysosomes and from the plasma membrane to endosomes.

    • COPII-coated vesicles: Move from the ER to the Golgi cisternae.

    • COPI-coated vesicles: Involved in retrograde transport from the Golgi back to the ER.

  • Coat Protein Functions:

    • Helps shape the membrane into a bud.

    • Captures molecules for onward transport.

Vesicle Budding and Fusion

  • Three well-characterized vesicle coat proteins and their functions:

    1. Clathrin

    2. COPI

    3. COPII

  • Functionality of budding and fusion includes:

    • Proper selection of cargo molecules during vesicle formation.

    • Ensures vesicles dock and fuse accurately with target membranes using specific SNARE proteins.

Golgi Apparatus Structure and Function

  • Structure:

    • Composed of stacked cisternae (4-7 cisternae).

    • Divided into cis-Golgi network, medial, and trans-Golgi network.

  • Functions include:

    • Glycosylation: Adding carbohydrate groups to proteins.

    • Sphingolipid and Glycolipid Synthesis.

    • Proteolytic Processing: Processing of proteins to their active forms.

    • Protein Sorting: Directing proteins to their final destinations.

Steps of Vesicular Transport

  • Proteins exit the ER in COPII-coated transport vesicles, with different GTP-activated components involved in the budding and cargo selection.

  • Proteins are modified and sorted as they move through the Golgi via:

    • Transport vesicles.

    • Cisternae migration.

Proteolytic Processing Example: Insulin

  • Insulin undergoes proteolytic processing during vesicle formation and maturation:

    • Proinsulin is cleaved into active insulin as it matures in secretory vesicles.

Transport Mechanisms from Golgi to Plasma Membrane

  • Cis Face: Receiving side from rough ER.

  • Trans Face: Shipping side directed toward the plasma membrane.

  • Vesicles transport glycoproteins, cholesterol, and membrane components.

Significance of SNARE Proteins in Fusion

  • SNARE proteins facilitate the fusion of vesicles with target membranes by ensuring specificity through matching v-SNAREs and t-SNAREs.

  • Fusion process illuminates how vesicles can deliver contents and integrate their membrane with the target membrane, critical for cell communication and function.

Conclusion

  • Vesicle transport is a vital cellular function—understanding mechanism, involved proteins, and pathways highlights essential cellular processes affecting overall cell function.