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O2 pathways in trematode hemoglobin

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Globins are oxygen-storing proteins, vital to life. In our blood, hemoglobins carry oxygen from our lungs to every cell in our body. In our muscles, myoglobins keep reserves of oxygen to make sure it is available when needed. In some plants, leghemoglobins capture oxygen molecules that would otherwise be harmful to the production of ammonium necessary for the plant's survival. All these globins possess an iron-containig "heme", that grabs on to oxygen for a short time, and share the same protein architecture, despite large variations in their sequences. Since the heme group is buried inside a globin, scientists wondered how oxygen makes its way inside the protein to reach it. Exploring the motion and energetics of globins using the program NAMD researchers learned to gather data that permitted them to visualize, utilizing the VMD software, all the pathways taken by oxygen migrating inside whale myoglobin (see the Aug 2006 highlight and related publication). However, when the researchers turned their attention to the rest of the globin family to compute their oxygen pathways, they found, on their computational spelunking trip, something surprising. Given the conserved architecture of all globins, they expected to see similar oxygen pathways throughout the globin family, but they saw the opposite! Aside from a conserved pocket right at the heme binding site, the distribution of oxygen pathways showed very little similarity from one globin to the next. This result is described in a recent report, which shows that oxygen-pathways are not conserved by evolution, and that their location is not determined by a protein's overall architecture, but rather by its local amino acids. The researchers also learned which amino acids are found more often than others lining oxygen pathways, recognizing that bulky side groups are not hindering, but favoring oxygen passage. More information can be found here.