Consider cargo proteins that are destined for secretion to the extracellular spa
ID: 163252 • 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) Normal Sar1 is mutated so that it hydrolyzes GTP immediately after binding GTP.
(ii) The signal recognition particle is mutated to be unable to bind to the SRP receptor.
(iii) Both
Explanation / Answer
i) Sar1 is essential for vesicle formation to transport the secreted protein from ER to Golgi and Sar1 GTP bound is active form. When GTP is hydrolyzed immediately after binding, vesicle cannot form and transport protein to golgi. So the protein remains in ER lumen itself.
ii) Only with the help of signal peptide, the secreted proteins are targeted to their respective organelles or to extracellular space. Binding of signal recognition particle to the signal peptide allows it to bind to the (SRP)receptor of endoplasmic reticulum after translation of protein. so the hindrance in the first step keeps the secreted protein in the cytosol itself.
iii) When both are mutated that is SRP and Sar1, secreted protein remains in the cytosol