 The last of the three four helical bundled proteins we're going to be looking at was hemorrhytrin looking like this This is a small protein that has evolved to have functionality quite similar to hemorrhmiaglobin that we're going to be looking at later. So here we have evolved a binding site that can bind oxygen on the interior, not through a heme group or anything But you have other ways of binding a few metals and a hydrophobic interior site here And these two irons typically then in turns bind oxygen. They don't bind it as an O2 molecule as hemoglobin does We'll talk about that later in the class, but rather binds us as an OOH- group So it's literally creating a bond to the oxygen Just as hemorrhmiaglobin, these molecules exist in two shapes or forms You can have a monomere of it or in this case a tetramere or a trimer or occasionally tetrameres And they will have slightly different properties whether you're binding oxygen in blood or tissue such as muscles You will not have these in your bodies. They typically occur in invertebrates in particular marine invertebrates such as brachiopods Exactly why is beyond the topic of this particular lecture at least But you see the parallel here. Nature has evolved multiple ways to bind oxygens This has different properties than hemorrhmiaglobin exactly what those properties are is irrelevant right now But usually you tend to have simpler proteins in lower Lower simpler smaller organisms while higher organisms, vertebrates have evolved more complex systems There is a cost to those complex systems that we will come back to in evolution So it's not always an advantage to have this nervous system this particular protein is a Four-helical bundle Likely because those four helices essentially help us to create an interior So if you look at these four pens right if you carefully select amino acids on the inside here to make the four-helical bundle Hydrophobic on the inside while hydrophilic on the outside We're basically creating a pocket a pocket that combines something that does not like water such as the metal environment and everything in here and The oxygen itself which is a gas is hydrophobic and that means that the oxygen molecules will be able to diffuse here bind and then at some later Point they should be released from the hemorrhid right again There is a reason why I'm showing hemorrhid to you first to show that it's this diversity in the four-helical bundles and Second this concept of carefully designing or in nature's case evolving the amino acids is something that shows up over and over again in reuse or possibly design