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<\/span>\n\t\t\t<\/div>In addition to lipids, biomembranes contain a myriad of proteins that either bind to the membrane surface (\u201cperipheral\u201d) or insert into it, passing through the bilayer from one side to the other (\u201ctransmembrane\u201d). It was observed previously that the leaflet asymmetry of the plasma membrane is mirrored in the shape of the membrane-spanning portions of transmembrane proteins. <\/span><\/p>\n<\/div>\n<\/div>\n<\/div><\/div>\n\t\t\t<\/div>\n\t\t\t<\/div>\n\t\t\t\t\n\t\t\t\t\n\t\t\t\t\n\t\t\t\t\n\t\t\t<\/div> Lorent et al<\/em>. go significantly beyond this finding: since the shape of that transmembrane region can be readily inferred from the protein sequence, one can infer the asymmetry of biomembranes belonging to intracellular organelles that are difficult or impossible to isolate and probe directly. For instance, their paper shows that the asymmetry of endosomal or lysosomal membranes very closely resembles that of the plasma membrane. In contrast, other organelles, such as the endoplasmic reticulum or the Golgi apparatus, have proteins with symmetric transmembrane regions, suggesting that their host membranes are symmetric as well.<\/span><\/p><\/div>\n\t\t\t<\/div>\n\t\t\t<\/div>\n\t\t\t\t\n\t\t\t\t\n\t\t\t\t\n\t\t\t\t\n\t\t\t<\/div> Even more interestingly: Lorent et al<\/em>. applied the same analysis to a wide variety of different organisms, such as amphibians, worms, and even fungi\u2014a broad survey of \u201ceukarya\u201d, one of the three big domains of life. The plasma membranes in all these organisms were found to be asymmetric; in fact, they closely matched the asymmetry of our own cells. This leads to a deep conclusion: while we do not yet know the ultimate reason or purpose for biomembrane asymmetry, the fact that it is so widely conserved across such a broad spectrum of organisms implies that it must be fundamentally important.\u00a0<\/span><\/p><\/div>\n\t\t\t<\/div>\n\t\t\t<\/div>\n\t\t\t\t\n\t\t\t\t\n\t\t\t\t\n\t\t\t\t\n\t\t\t<\/div> This is an exciting result about the biological importance of membrane asymmetry, which underscores its ubiquity and poses a host of new questions. It also happens at a time where membrane biophysicists have devised several new experimental methods for artificially creating and examining asymmetric membranes. These provide a simplified test system for investigating the many ways in which asymmetric membranes differ from their symmetric counterparts, and how these differences could point us to the physiological purpose of asymmetry. For instance, it has been speculated that the higher degree of disorder in the inner leaflet of the plasma membrane makes it ideal for protein rearrangements and signaling, but at the same time the widely studied \u201clipid rafts\u201d, believed to be signaling platforms, are formed in the outer leaflet. Uncovering how these connections work is important for understanding many human diseases that arise if such signaling goes wrong, which shows that exploring the physiological basis for asymmetry could help combat such diseases.<\/span><\/p><\/div>\n\t\t\t<\/div>\n\t\t\t<\/div>\n\t\t\t\t\n\t\t\t\t\n\t\t\t\t\n\t\t\t\t\n\t\t\t<\/div>\n\t\t\t\t\n\t\t\t\t\n\t\t\t<\/div> Living cells and many of their internal organelles are bounded by a membrane composed predominantly of lipids. These are molecules with a water-soluble head region and a water-insoluble tail region. As a result, they form a bilayer structure, with the tail regions facing each other and the head regions facing the water.\u00a0[…]<\/p>\n","protected":false},"author":5,"featured_media":597,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"on","_et_pb_old_content":"","_et_gb_content_width":"","footnotes":""},"categories":[9],"tags":[],"class_list":["post-521","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-great-papers"],"jetpack_featured_media_url":"https:\/\/research.phys.cmu.edu\/biophysics\/wp-content\/uploads\/sites\/2\/2020\/07\/long-lipid-bilayer-sim-5-scaled.jpg","_links":{"self":[{"href":"https:\/\/research.phys.cmu.edu\/biophysics\/wp-json\/wp\/v2\/posts\/521","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/research.phys.cmu.edu\/biophysics\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/research.phys.cmu.edu\/biophysics\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/research.phys.cmu.edu\/biophysics\/wp-json\/wp\/v2\/users\/5"}],"replies":[{"embeddable":true,"href":"https:\/\/research.phys.cmu.edu\/biophysics\/wp-json\/wp\/v2\/comments?post=521"}],"version-history":[{"count":40,"href":"https:\/\/research.phys.cmu.edu\/biophysics\/wp-json\/wp\/v2\/posts\/521\/revisions"}],"predecessor-version":[{"id":2454,"href":"https:\/\/research.phys.cmu.edu\/biophysics\/wp-json\/wp\/v2\/posts\/521\/revisions\/2454"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/research.phys.cmu.edu\/biophysics\/wp-json\/wp\/v2\/media\/597"}],"wp:attachment":[{"href":"https:\/\/research.phys.cmu.edu\/biophysics\/wp-json\/wp\/v2\/media?parent=521"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/research.phys.cmu.edu\/biophysics\/wp-json\/wp\/v2\/categories?post=521"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/research.phys.cmu.edu\/biophysics\/wp-json\/wp\/v2\/tags?post=521"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
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by: Markus Deserno, Muhammed Erg\u00fcder, Samuel Foley, Amirali Hossein, and Malavika Varma<\/p><\/div>\n\t\t\t<\/div>\n\t\t\t<\/div>\n\t\t\t\t\n\t\t\t\t\n\t\t\t\t\n\t\t\t\t\n\t\t\t<\/div>
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Living cells and many of their internal organelles are bounded by a membrane composed predominantly of lipids. These are molecules with a water-soluble head region and a water-insoluble tail region. As a result,<\/span> they form a bilayer structure, with the tail regions facing each other and the head regions facing the water.\u00a0Lipids come in a variety of types, and the lipid composition differs between the two sides of a biomembrane.<\/span><\/p><\/div>\n\t\t\t<\/div>\n\t\t\t<\/div>