In the 1980s, efforts to determine the structures of all known proteins needed to overcome one large – or more accurately speaking, microscopic – barrier. Many proteins involved in vital biological functions, such as the transport of nutrients into cells or nerve impulses, span the fatty membranes that surround every cell in order to carry out their tasks. Buried within the membrane as they are, these important proteins were long thought to be impossible to access and crystallize for structural studies.
The seemingly impossible was at last achieved by Hartmut Michel, Johann Deisenhofer and Robert Huber, for which they received the Nobel Prize in Chemistry in 1988. The source of their breakthrough work was not just any membrane protein, but the hub of possibly the most important chemical reaction on earth – photosynthesis – in which plants and bacteria convert the energy of the sun into chemical energy to fuel their growth.
In 1982, Hartmut Michel developed a new isolation procedure that helped him obtain the first crystals of a four-protein complex, called a photosynthetic reaction centre, that is crucial to the process of photosynthesis in the purple bacterium Rhodopseudomonas viridis. Michel collaborated with Johann Deisenhofer and Robert Huber to analyse these crystals using X-ray crystallography, and through this they determined the exact arrangement of the more than 10,000 atoms that make up the three-dimensional structure of this photosynthetic reaction centre.
The photosynthetic apparatus in bacteria might be simpler than in plants, but Michel, Deisenhofer and Huber's findings showed there is a close relationship between the bacterial reaction centre and the protein complex in plants, providing a giant leap in the general understanding of the mechanism of plant photosynthesis. But more than that, their findings also gave the green light to researchers to finally access and explore a raft of other important proteins housed in the cell's living frontier.