Myoglobin

Myoglobin is a very common protein in red blood cells. Its "duty" is to store oxygen and only under extreme conditions it releases the oxygen. So, it has a higher affinity for oxygen than hemoglobin has. It is almost identical to a single unit of hemoglobin. Anyway, I will not go into details and if you want to learn more about it, you can just read a Biochemistry textbook or even google it.

Another reason why it is a special protein is that it was the first protein that was "solved." After years of work, John Kendrew and his team finally solved the structure of the protein and built a model. Below is the model and I have learned that you can visit it at Science Museum in London. Unfortunately, it looks disgusting. I wish they had chosen a better color and material to build the model.

http://www.sciencemuseum.org.uk/images/i053/10321094.aspx

And here is a model generated by PyMOL on my laptop. It looks cute now: