Consider cargo proteins that are destined for secretion to the extracellular spa
ID: 163338 • Letter: C
Question
Consider cargo proteins that are destined for secretion to the extracellular space. For each of the following pairs of mutations or conditions, predict where the cargo will end up (ex. in the cytoplasm, a specific organelle, transport vesicles, multiple places, extracellular space) for: (i) & (ii) Each individual condition; & (iii) The combination of both.
(i) A mitochondrial signal sequence is added to the C-terminus of the cargo protein.
(ii) v-SNAREs on COPII coated vesicles are mutated to be unable to bind t-SNAREs
(iii) Both
Explanation / Answer
(1). If a mitochondrial signal sequence is added to the c- terminus of the cargo protein, it will end up in the endoplasmic reticulum (a specific organelle).
(2). Vesicular transport
COP-2 carries cargo protein in an anterograde direction, i.e, from the ER to the golgi.
V-snare is a vesicle protein on the outside that is complementary to a t- snare protein on the target organelle. This ensures that vesicle goes to the right place. V-snare and t-snare attach each other in a coiled coil fashion. Once they are coiled around each other, they promote fusion of the two membranes. Botox cleaves a particular v-snare located on neurotransmitter vesicles at a neuromuscular synapse, thereby preventing vesicles carrying neurotransmitter to fuse with the surface membrane. Failure to release neurotransmitter causes muscular paralysis.
Vehicle fusion is mediated by the interaction between specific pairs of proteins called as SNAREs. The formation of complexes between v-snares on the vesicle and t-snares on the target membrane leads to membrane fusion and completes the process of vehicle transport since v-snares are complementary to t-snares. So if v-snares on cop2 coated vesicles are mutated and unable to bind t-snares, then membrane fusion does not occur which leads to the complete disruption of vesicular transport system.