September 22, 2017 at 10:25PM

Today I learned: 1) One of the major bacteria protein secretion tags works by getting itself inserted into the plasma membrane and esposing a motif that's recognized by a membrane-bound protease. The motif gets clipped, the tag stays in the membrane, and the rest of the protein floats away. 2) GFP doesn't really work in plants. Chlorophil blocks either GFP's absorption or its emission, and plants typically have a lot of chlorophil. Instead, the standard plant reporter is (one of the many) luciferase(s), which produces a fluorescent small molecule. Unfortunately, luciferase doesn't really work unless you express it in the chloroplast. I don't know why. Something about "metabolism". Anyway, even *more* unfortunately, the "express luciferase in the chloroplast" technology is under patent, so you can't really make glowing green plants for commercial use. =( Fortunately, it doesn't matter much, because 3) There's a class of lipids that act as membrane-specific markers for eukaryotic cells. I can't remember their name right now, and I can't find them, so I'm just going to call them marker lipids. Anyway, there are several (about a dozen) variations of marker lipid, and each is used by the cell to label a different kind of membrane, i.e., marker type I goes on the nuclear membrane, marker type II goes on the endoplasmid reticulum, marker type III goes on the plasma membrane, etc. That's how the cell can correctly insert stuff into the right membrane -- a lot of membrane insertion will only happen on membranes bearing the right marker lipid, and some proteins don't function unless they're bound to the right marker lipid. How, then, do the marker lipids get into the right membrane? Well, they can all be interconverted by a bunch of different enzymes, and those enzymes are *themselves* bound to the right membrane. So, using my example marker lipids above, the enzymes that turn other marker lipids into marker type I are found on the nuclear membrane. That way, just about any marker lipid can go into just about any membrane, and will eventually be converted into the right kind. How, then, do the marker-lipid-converting enzyems get into the right membrane? They recognize the marker lipids, of course!