March 11, 2016 at 02:49AM

Today I Learned: 1) Amphiphilic peptide membranes. Consider a cell membrane. Cell membranes are usually phospholipid bilayers, which is a fancy way of saying they're basically a soap bubble made from a ton of insoluble hydrocarbon chains (lipids) with phosphate groups at one end that are soluble (phospholipids), which organize into a double-layered sheet with the heads facing out towards water and the tails facing inward towards each other. In principle, you should be able to build such a membrane out of any molecule of roughly the same shape (long and thin) and size with a charged head and a long, insoluble tail. Well, some clever chemist came up with another class of molecule that fits the bill -- amphiphilic peptides. These are very short proteins (amino acid chains) where the first amino acid is charged and the rest form a long, hydrophobic backbone. In in-vitro conditions, they can spontaneously form micelles and bilayers just like phospholipids, although so far they've all been pretty small (tens of nanometers at the largest). Why would you use amphiphilic peptides instead of phospholipids? After all, phospholipids are good enough for nature*, why aren't they good enough for us? The answer is their programmability. Because amphiphilic peptides are, well, amino acid chains, they can be genetically encoded. If they can be genetically encoded, they can be easily modified. I'll leave it at that for now. Thanks to Anders Knight for cuing me in to amphiphilic peptide membranes! He's been reading about them extensively over the last 24 hours or so, so you should direct any questions about peptide membranes to him (and direct his answers back to me!). * ...or maybe not. See #2. 2) There is at least one context in which the usual phospholipid bilayer membrane design is not good enough for nature, and that's in the extremophiles. Archaea and bacteria living at extremely high temperatures (anywhere from about 50-100 °C) have some really crazy phospholipids in their membranes, presumably because normal phospholipids either break down or fly apart from their neighbors under very hot conditions. Then again, a lot of those lipids can also be found in the membranes of archaea at perfectly reasonable temperatures, so they might not have anything to do with living at high temperatures at all. For more information on archaeal phospholipids than you ever knew existed, check out http://ift.tt/1nBVqHN (apologies if it's behind a paywall). In particular, check out figure 1, which shows a bunch of interesting archaeal and bacterial lipids. My favorites are caldarchaeol (1d) and cyclopentane-containing caldarchaeol (1f), which have two phospholipid heads! 3) "Psychrophilic" is another word for "cryophilic", which is used to describe organisms that grow in extreme cold (between -20 and 10 °C).