The crystal structure of a molecule from a primitive fungus has served as a time machine to show researchers more about the evolution of life from the simple to the complex.
By studying the three-dimensional version of the fungus protein bound to an RNA molecule, scientists from Purdue University and the University of Texas at Austin have been able to visualize how life progressed from an early self-replicating molecule that also performed chemical reactions to one in which proteins assumed some of the work.
"Now we can see how RNA progressed to share functions with proteins," said Alan Lambowitz, director of the University of Texas Institute for Cellular and Molecular Biology. "This was a critical missing step."
Results of the study were published in Thursday's (Jan. 3) issue of the journal Nature.
"It's thought that RNA, or a molecule like it, may have been among the first molecules of life, both carrying genetic code that can be transmitted from generation to generation and folding into structures so these molecules could work inside cells," said Purdue structural biologist Barbara Golden. "At some point, RNA evolved and became capable of making proteins. At that point, proteins started taking over roles that RNA played previously - acting as catalysts and building structures in cells."
In order to show this and learn more about the evolution from RNA to more complex life forms, Lambowitz and Paul Paukstelis, lead author and a research scientist at the Texas institute, needed to be able to see how the fungus' protein worked. That's where Golden's team joined the effort and crystallized the molecule at Purdue's macromolecular crystallization facility.
"Obviously, we can't see the process of moving from RNA to RNA and proteins and then to DNA, without a time machine," Golden said. "But by using this fungus protein, we can see this process occurring in modern life."
Looking at the crystal, the scientists saw two things, Golden said. One was that this protein uses two completely different molecular surfaces to perform its two roles. The second is that the protein seems to perform the same job that RNA performed in other simple organisms.
"The crystal structure provides a snapshot of how, during evolution, protein molecules came to assist RNA molecules in their biological functions and ultimately assumed roles previously played by RNA," Golden said.