Membrane fusion Flashcards
steps of membrane fusion
- tethering
- docking of a trans-SNARE complex
- membrane fusion
how close do membranes need to be apart to enable fusion
closer than 1.5nm
the movement of membranes from one compartment to another allows exchange of
1) membrane proteins
2) luminal content.
describe the role of tethering factors
MTCs provide a protein bridge between two membranes
they provide some specificity to the fusion process
give an example of a tethering factor
HOPS complex will tether lysosomes to late endosome before the SNAREs allow fusion
role of SNARE proteins
bring membranes into close proximity, which allows repulsion forces between membranes to be overcome, thereby allowing membranes to ‘fuse’
they also provide specificity to membrane fusion events
how many helical coils does a SNARE complex consist of
4
SNAP proteins contribute 2
features of a SNARE complex
SNAREs have a hydrophobic central core, hydrogen bonding and salt bridges
Q snares –> contribute Glutamine
R snares -> contribute arginine
A SNARE complex consists of 3 Q-SNARES (Qa, Qb and Qc) and one R-SNARE.
SNAP {no.} proteins have Qb and Qc helices
position of the N & C terminus of SNARES
The N-terminus of the SNAREs are always pointing into the cytoplasm
The C-terminus of the SNAREs are either luminal or extracellular
what did the SNARE experiment show?
SNAREs are the minimal machinery needed for membrane fusion
how do you recycle SNARE proteins
use alpha-SNAP and NSF
what is the process behind NSF and aSNAP
NSF and aSNAP form a complex and with the hydrolysis of ATP break open the SNARE complex allowing the SNARE proteins to be re-used
NSF - hydrolyses ATP
aSNAP - binds and activates NSF ATPase activity
which proteins can regulate SNARE complex assembly
SM proteins by either providing positive or negative regulation
SM proteins can regulate SNARE protein conformations
What are Rab proteins? and what is their involvement with SNARES
Rab proteins are GTPases
Rab proteins which can bind/recruit a variety of effector proteins can regulate SNARE fusion
Active Rab proteins make membrane fusion permissible, and regulate the speed of the fusion event (alongside SM proteins)
