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We are looking at modifying the signal peptide of a receptor in a common immortalized human cell line. The cell line already expresses an unusually high amount of the protein, but much of it is not surface expressed.

When we compared the sequence of the signal peptide in the cell line (in this specific case the first 19AA), we found 2 mutations vs the wild type (WT) sequence. One obvious idea, which we will do, is to restore the peptide to the WT version.

But I've been curious about options that increase trafficking to the plasma membrane over WT. When I've looked up groups that have actually done this, it's normally been with large screens against every possible mutation in the signal peptide.

Are there targeted approaches to choosing a small number of signal peptides to increase surface expression?

I'm playing around with swapping it out some viral peptides that are totally unrelated to see if we can get increased expression with a receptor that's still (semi) functional.

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    $\begingroup$ Is there any evidence for the idea that the signal sequence is the cause of the lack of surface expression? Do you know where the rest of the protein (not at the surface) actually is located? $\endgroup$ – Alan Boyd Aug 14 '17 at 17:19
  • $\begingroup$ From staining it seems to mostly be diffuse through out the cytoplasm, not really in puncta as I would have thought from miss-folding. We also know that what is surface expressed is functional. $\endgroup$ – Atl LED Aug 14 '17 at 17:22
  • $\begingroup$ Further I'm interested in the general case if there is one, type-I transmembrane proteins if a type is needed. I will say that interested in any particular modification, even if it's a signal peptide not found in the host (eg viral). I'm trying to get my tech transfer guys to clear me asking about the specific protein. $\endgroup$ – Atl LED Aug 14 '17 at 17:50
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    $\begingroup$ I don't have an answer to the question but I'm intrigued by the problem. Do the mutations look like they might affect SP function? Meanwhile here is a paper on overall design principles that you may not have seen. It's old, but it's by G von Heijne. $\endgroup$ – Alan Boyd Aug 14 '17 at 18:22
  • $\begingroup$ @AlanBoyd Any von Heijne is worth reading regardless of application. That was the main source that lead me to ask the question. $\endgroup$ – Atl LED Aug 14 '17 at 19:49
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You could upregulate the transcription of the receptor gene you are interested in. More receptors being produced = more receptors being expressed on the cell's surface.

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