You are trying to design a protein that will be expressed in Escherichia coli and secreted outside of the cell for purification and use as a pharmaceutical. E. coli is a gram-negative cell and the protein folds after it has exited the cell. Which secretion system would work best for this project? Support your answer with evidence based on the properties of E. coli, the protein, and the secretion system.
What will be an ideal response?
Answer: Answers should refer to the fact that E. coli is gram negative and thus has both a cytoplasmic and outer membrane. In order to secrete the protein a translocase that can move the protein through the outer membrane will be necessary. The protein folds after it has left the cell, thus the Sec system would work better than the Tat system, because the Tat system is specialized for proteins that fold in the cytoplasm and then cross the cytoplasmic membrane. Together these properties dictate that a two-step mechanism, such as a type II secretion system would work best for this project.
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