Vesicular Transport Lecture Notes

Introduction

• Detailed discussion on vesicular transport.
• Focus on endoplasmic reticulum (ER) and Golgi apparatus (GGI).

Protein Translation and Translocation

• Proteins encoded by the genome, transported mRNA to ribosome.
• Translocated into the ER.
• Vesicular trafficking process for protein transport.

Types of Transport Vesicles

COP II Coated Vesicles

• Mediate anterograde transport from ER to CIS GGI.
• Movement towards the outside of the cell.

COP I Coated Vesicles

• Mediate retrograde transport from CIS GGI back to ER.

Clathrin Coated Vesicles

• Transport from plasma membrane to endosome.
• Diverse utility and types of transport dependent on complex association.

Vesicle Budding and Fusion

Anterograde Transport

• Two key events: budding from ER, fusion to target membrane (CSI).
• GTP-binding proteins assembly leads to vesicle release.

Vesicle Fusion

• Involves SNARE proteins: V-SNAREs (vesicle-bound) and T-SNAREs (target-bound).
• Interaction brings membranes close, allowing content release.

Molecular Machinery

COP II Vesicles

• Coats: SEC 23, 24, 13, 31, 16.
• GTPase: Sar1 GTPase.

COP I Vesicles

• Coats: seven different COP subunits.
• GTPase: ARF GTPase.

Clathrin-Mediated Transport

• Complexes: Clathrin and AP1, GGA, AP2, AP3.
• GTPase: ARF GTPase.

GTP Hydrolysis and Vesicle Assembly

• GTP hydrolysis powers assembly.
• Sar1 GTP replaces GDP and embeds into the membrane.
• Membrane carving proteins form vesicle curvature.
• Vesicle becomes naked after GTP hydrolysis leads to coat disassembly.

Endocytosis

Types of Endocytosis

• Receptor-mediated endocytosis.
• Phagocytosis and pinocytosis.

Receptor-Mediated Endocytosis

• Involves adapter proteins, AP2 complexes, and clathrin assembly.
• Dynamin aids in vesicle pinching.

Vesicle Tracking in Live Cells

• Label vesicles using fluorescent tags for live cell imaging.
• Track motion and dynamics using time-resolved fluorescence microscopy.

Conclusion

• Overview of retrograde and anterograde transport by COP I, COP II, and clathrin-coated vesicles.
• Techniques to study vesicle trafficking in live cells.