Talk:Peripheral membrane protein

message: The article says that "Peripheral membrane proteins are proteins that adhere only temporarily to the biological membrane with which they are associated". I think there is a big confusion between peripheral and monotopic membrane proteins. "Peripheral" means a biochemical point of view on membrane proteins. Peripheral proteins are proteins weakly bound to the membrane and require a soft treatment (e.g. high salt concentration) to be realesed. These proteins do not necessarly interact directly with the membrane. They can just be bound to an integral membrane protein. On the opposite, an integral membrane protein requires the strong detergent compund to be released from the membrane (i.e. the membrane has to be broken). This is also a biochemical point of view on membrane proteins. In contrast, monotopic and polytopic is related to a structural point of view. That means the protein is in contact with one or both compartments defined by the membrane. A monotopic protein can be an integral protein if it strongly interact with the membrane like a GPI-anchored protein  or a protein anchored by an amphipathic alpha-helix (e.g. some antibacterial peptides, but it is strongly case-dependant). As far as I know, only monotopic bound to the membrane surface with electrostatic interaction are also peripheral proteins in all cases. Finally, the notion of "temporarly" bound is very weak to my opinion. There is several example of transmembrane proteins that are not initially inserted in the membrane (VAMP, Bcl2, some bacterial toxin if I remember well) They can't be classified as peripheral, regarding the difficulty to extract them once they become inserted... I don't have enough time to correct everything but I'm pretty sure that wikipedians will found enough references in Pubmed to correct this article. —The preceding unsigned comment was added by 136.159.234.195 (talk) 17:05, 4 April 2007 (UTC)
replies: text: It is already written in the first paragraph: "In contrast to integral membrane proteins, peripheral membrane proteins tend to collect in the water-soluble component, or fraction, of all the proteins extracted during a protein purification procedure." One could also argue that Bcl2 and some bacterial toxins have two different conformational/aggregation states, one of which is integral membrane state, and another is water-soluble state (not necessarily even "peripheral"). Thus, the same protein can behave as integral or peripheral, depending on conditions. Some classical peripheral proteins, such as annexins, can undergo conformational changes and aggregate with lipid bilayer irreversibly. You are very welcome to edit and improve the article or provide good sources that would clarify the situation. Biophys 18:23, 4 April 2007 (UTC)
replies: text:  Nice to see that we agree on the complexity of the problem. Atually, I was a little bit worried about the lack of moderation of the first sentences... Many examples show that it not so simple that's why so many people are working on the membrame-protein interaction. :) Unfortunately, I can't do much more than a comment : I'm very busy and Wikipedia become quickly too time-consuming -- 136.159.234.195 23:01, 4 April 2007 (UTC)
thread_title:  About the definition of Peripheral membrane proteins 

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