After having attended lecture and read the paper by Cabezon et al. (2015), you s
ID: 226759 • Letter: A
Question
After having attended lecture and read the paper by Cabezon et al. (2015), you should have a pretty good grasp of the complexity of bacterial conjugation. Please answer the following questions. a. Pilin is translated in the cytoplasm and somehow magically ends up outside the cell where it forms the tubular pilus. Please provide evidence that you understand the basic principles by which this happens including the role of the signal sequence, the importance of hydrophobicity, and the role of ATPases. b. Once you build the pilus, somehow the cell is able to transport the "DNA cargo from one bacteria to the other. Please provide a nice concise overview, establishing that you understand the process of cargo delivery by summarizing the distinct step of transport and how the cell provides energy to do this work.Explanation / Answer
a) Secreted proteins have signal sequence or signal peptide with 10 - 20 aminoacids at the N- terminal of the secreted protein. This signal sequence is essential to transport the secreted proteins to its desination. In this case, pilin is secreted in the cytoplasm and which is transported to the outer layer of the cell.
During or after complete translation of pilin, it is targeted to the membrane. The N-terminal will be anchored in the plasma membrane by hydrophobic domain of the pilin while the C terminal will be present in the periplasm. ATPases support the assembly of the pilin subunits in the outer membrane to form tubular pilus facing the extracellular region. Hydrophobic domains in the pilin protein plays an important role in anchoring the polar regions of protein to form tubular pilus. This type of ATP dependent process is called Type-IV secretion system and one of the main function is DNA transfer (conjugation).
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