Vesicle Docking and Fusion

Vesicle Fusion to the Correct Membrane

  • The process ensures vesicles fuse to the correct target membrane for exocytosis.

  • It involves proteins on the target membrane that capture the vesicle and bring it close for interaction and fusion.

Tethering Proteins

  • These proteins extend from the target membrane and grab vesicles, pulling them closer.

  • Two types:

    • Coiled-coil tethering proteins: Located on the Golgi membrane, they interact with COP1 vesicles.

    • Multi-subunit tethering proteins: Found on the plasma membrane, interacting with vesicles from the TGN (Trans-Golgi Network).

Vesicle and Membrane Proteins

  • Vesicle proteins:

    • V-SNARE (vesicle SNARE): Located on the vesicle.

    • Rab GTPase: Also on the vesicle.

  • Membrane protein:

    • t-SNARE (target SNARE): Located on the target membrane.

SNARE Interactions and Fusion

  • SNARE Definition: SNARE stands for Snap Receptor.

  • Tethering complexes bring the vesicle close, enabling the T-SNARE and V-SNARE to interact.

  • Initial binding is weak; Rab GTPase catalyzes a reaction to lock them together.

  • This secure connection between T-SNAREs and V-SNAREs forces the vesicle to fuse with the target membrane via exocytosis.

Recycling Proteins

  • Following fusion, Rab GTPase and V-SNARE need to be removed and recycled for future use.

  • Two proteins, SNAPs and NSF, facilitate this:

    • They cause the V-SNARE and T-SNARE to detach from each other.

    • Rab GTPase is released.

    • All components are then available for reuse in subsequent vesicle formation.

  • The vesicle becomes integrated into the target membrane.

Snares and Neurotransmitter Release

  • SNAREs are vital for neurotransmitter release, which requires vesicle fusion.

  • Botox interferes with muscle contraction by cleaving SNAREs.

    • This cleavage disrupts the release of neurotransmitters needed to trigger muscle contraction.

    • The result is muscle paralysis, which is used cosmetically to reduce wrinkles.

  • Botox works by preventing the interaction of V-SNAREs and T-SNAREs, thus blocking vesicle fusion.