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Thread: difference in protein composition of the nucleolemma

  1. #1 difference in protein composition of the nucleolemma 
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    It's as the title says: what's the reason that the inner nuclear membrane and the outer nuclear membrane (separated by the perinuclear space) have a different protein composition? while it is actually a continuous layer...

    The only reasons i can think of is: protein synthesis only occurs on the outer membrane since it is the continuation of the rer or that perhaps the nuclear pore complex form a barrier between the outer and inner membrane.

    Can someone help me out here...

    Thanks in advance!

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  3. #2  
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    Not my area of expertise by a long shot, but if you think of a somewhat-analogous system, the bacterium, it makes more sense. The two membranes have different functions. In bacteria (as I understand it), the outermost membrane is more of a coarse filter, while the inner membrane exerts precise control over what gets in. The protein composition is going to NEED to differ in that case to facilitate those functions.

    I like your reasoning behind it. The real answer could be very complicated, so any reasonable answer you come up with ought to be plausible.

    It might also be worth considering what environments each membrane "sees." The outer membrane interacts with the cytoplasm, and the inner membrane interacts with the nucleoplasm. WAY different things going on in each compartment. You will need to have different proteins in order to best mediate interactions here, and I don't think it would be all that useful to get into specifics.

    But there is one! PTP1B has been shown to localize to the inner nuclear membrane, according to John Chernoff. Exactly what the heck it's doing there is still a very active area of research, but to his knowledge it's the only tyrosine phosphatase that does that. Here's a paper on the phenomenon, which is available for free through the PMC.

    So you have different proteins localizing. That's an interesting phenomenon! You SUMOylate the PTP1B, and it specifically goes to the inner membrane. The only way this is possible is if you have SUMO recognition SPECIFICALLY on the inner membrane! That would require receptors that are not present on the outer.

    So that's a long-winded and specific example of why you need separate compositions. The two compartments have different function.

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  4. #3  
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    Compartmentalisation of function within membrane-bound regions, as Deadally notes, is a key feature of eukaryotic cells. So we can already "deduce" that any unique proteins within that region are going to have some compartment-specific functions.

    A major role for the IM is as a component of the nuclear lamina. Many of the IM proteins are likely to be structural components of the nuclear lamina and thus will be involved in DNA packaging within the nucleus. This control of large-scale chromatin structure means that IM proteins possibly influences gene epxression too.
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  5. #4  
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    Prote´n synthesis only occurs outside the inner membrane. So the prote´ns that need to be in the inner membrane, need to look different, to pass this membrane. Not sure if they need to lock to a detector, or simply pass trough it because of their smaller/conveniŰnt shape. But prote´ns are formed to where they are needed. So this is probably why they are different.

    They also have a different goal. Inside the membrane, all one needs to do, is read DNA, create cRNA, create cDNA (division), transport cRNA outside the inner membrane, and create/transport ATGCU's.

    But the idea itself splits the proteins in the cell into 2 groups. Which i find deserves more study .
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  6. #5  
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    I concur with the above posts.

    Note that just because membranes are continuous does not mean they necessarily have to have the same composition. There are countless examples. Note the differing profiles of basal and apical membranes of any given cell, e.g. enterocytes, renal tubule cells, endothelial cells, etc. Note that neurons have higher concentrations of potassium and sodium channels at nodes of Ranvier compared with parts of the membrane surrounded by myelin…..and the list goes on.

    So your question was about why a continuous membrane may have various compositions throughout rather than how? (i.e. the mechanism through which different membranes are produced) Because that is also interesting. The DNA does not code for all the membranes of the cell, the membranes need to be ‘inherited’ from the parent cell. Makes me wonder re the details of e.g. cloning a mammoth (resurrecting mammoths from their DNA) – would a surrogate species cell suffice (e.g. a modern elephant). (are there plenty of examples of this kind of thing I’m unaware of? Do species have species-specific membranes that can’t hold other species DNA?)
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