The interactions between proteins are of central importance for virtually every process in a living cell. It has long been a mystery how two proteins associate to form a complex in a complicated... Show moreThe interactions between proteins are of central importance for virtually every process in a living cell. It has long been a mystery how two proteins associate to form a complex in a complicated cellular context. Recently, it was found that an intermediate state called encounter state, of a protein complex, exists briefly before a final protein complex is formed. In the encounter state, one protein is rolling over on the surface of its partner, searching for the optimal orientation. In my PhD thesis, a transient electron transfer complex formed between a heme protein and an iron-sulfur protein was found to be trapped in this intermediate state, existing as a pure encounter complex. Thus, characterization of this dynamic complex by nuclear magnetic resonance spectroscopy advances our understanding of the general mechanism of protein-protein interaction Show less