 So if I have two beta sheets, I can either stack them on top of each other in an orthogonal fashion or in a parallel fashion. And again, these are real proteins, so you can forget about the perfect situations. But here you can likely see that they're packed roughly that way, and this one is at least more parallel, even if there is a bit of an angle between them. This particular protein is called fatty acid binding protein, and it's a friend we already looked at with that. I'll get back to that in a second, and this particular protein, I think that's an immunoglobulin that occurs in your immune system. In each layer, all of the strands are aligned, but in this case, between the two layers, there is roughly a 90-degree turn. Here too, the individual strands are aligned in each layer, and the two layers are also aligned. As a bit of an exercise, look at the geometry of these two structures and decide for yourself, are they parallel or anti-parallel? You should see that from the structure. This was the first protein, fatty acid binding protein. Is it parallel or anti-parallel? Anti-parallel. And that's characterized by these really short loops between them. This was an NMR structure I showed you before. Fatty acid binding protein has a couple of nice properties. It's using this feature of a beta sheet where every second amino acid is pointing to one side of the layer and every second amino acid to the other side of the layer. When this is constructed, each of these layers have hydrophobic on one side and hydrophilic on the other side. When we put both of these two together, you're actually going to have a very hydrophobic interior, but the entire exterior here is soluble. So this is, you could say that each layer is amphiphatic, meaning that it's, by the way, half of it is one side of it is hydrophobic, the other side is hydrophilic. Typical for detergents or anything that you use to solvate oil and water. The part that we're solvating here is that we're binding a fatty acid on the inside. I think I have an illustration of that shortly. This fold has a name. We occasionally call it a beta cylinder or beta barrel. It might not be entirely obvious, but again, we want to make sense of something and try to organize it hierarchically. That's characterized by something we call the beta meander. So meandering is this process that rivers show when they erode rocks or anything in nature. And what happens is that when the river changes direction, it's always eroding the rock when it's making the turn, and that means that you extend the river there. So the meandering part here is characterized by this, that we're having one sheet, and then we're making one short turn, and we directly continue with the sheet bound to the first. And then making one short while strand three is binding to strand two, etc. So there are no complications if that is super simple and easy and nice structure, but it has some drawbacks that you will see shortly.