Reconstitution of vesicle transport in cell-free systems was historically carrie
ID: 64221 • Letter: R
Question
Reconstitution of vesicle transport in cell-free systems was historically carried out in the presence of isolated “donor” and “acceptor” Golgi stacks. The donor stacks are isolated from cells expressing a viral protein and lacking a processing enzyme. The protein can be transported to the acceptor stacks (that do contain the processing enzyme) and be processed only in the presence of an energy source (such as ATP) and a cytosolic fraction. The transport vesicles that mediate this process are visualized by microscopy. Various compounds can be added to this system to help understand the mechanism of transport. Two such compounds were added in early experiments in the 1980s, both of which blocked transport of the viral protein and resulted in the accumulation of transport vesicles. However, the accumulated vesicles following treatment with one of these compounds (A) appeared to be coated, while those resulting from treatment with the other compound (B) did not. If one of these compounds is a nonhydrolyzable GTP analog and the other one is N-ethylmaleimide, which compound (A or B) do you think represents the GTP analog? Write down A or B as your answer and explain why.
Explanation / Answer
Compound A is the nonhydrolyzable GTP analog. This is because the compound A coated the vesicles and stopped the transport of viral protein and coated transport vesicles are accumulated. The compound B does not coat the transport vesicles and it is N-ethylmaleimide, a derivative of maleic acid containing imide functional group. Generally, it is an alkene. Since, hydrolyzing of GTP provides energy for binding and transport of compound, the nonhydrolyzable GTP coated the vesicles and thereby prevented the transport of viral proteins. Thus, compound A is the nonhydrolyzable GTP analog.
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