Topology of protein

Topology of protein

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The domain structure of protein Z, which is composed of 180 amino acids, is shown in the upper part of the figure below. Protein Z is palmitoylated at a cysteine residue (the third amino acid) through the mechanism shown in the box.

Which of the following diagrams shows the correct topology of protein Z in the plasma membrane?

I think the second diagram is correct because cytoplasmic side has reducing environment and so SH will not be allowed to react this way. Am I right ?

I don't think there's any oxidation or reduction going on in this reaction; certainly there is no net reduction or involvement of NADH cofactor or anything like that. Furthermore, I think that it isn't too hard (esp. since these are enzyme-catalyzed reactions) to imagine that the mechanism is simple: nucleophilic attack of the carbon of the thioester by the cysteine, forming a thioketal intermediate, resulting in ejecting the CoASH as a leaving group. No reduction or oxidation.

Instead of oxidation or reduction, I would think about where exactly are the components of each reaction present. In order for the palmitoylation reaction to occur, you need: the protein Z N terminus, palmitoyl-CoA, and protein acyltransferase. Where are these components more likely to be present, inside or outside of the cell? Especially given that CoASH has several negatively charged phosphate groups.

Watch the video: Endoplasmic Reticulum Protein Transport (December 2022).