MOSCOW, May 12. /TASS/. A team of biologists from Russia, the Czech Republic, Israel, the US and Spain have systematically measured how mutations interact within a protein coding gene. They studied tens of thousands of mutants of the green fluorescent protein from the jellyfish Aequorea victoria.
New results uncover mechanisms of protein evolution and deepen our understanding of why effects of mutations are dependent on the genetic context in which they occur, the Moscow Institute of Physics and Technology (MIPT) said on Thursday.
"We were curious about how accumulation mutations in a protein interact with each other, and how often does this happen in protein evolution," said Karen Sarkisyan, a researcher at IBCH RAS and the first author of the paper.
"We came up with an idea of how we can measure tens of thousands of protein mutants at the same time and applied it to study how the interdependence of the impact of mutations on the brightness of the green fluorescent protein," he said.
The team led by the evolutionary biologist Fyodor Kondrashov surveyed the so-called "fitness landscape", a concept that biologists use illustrate how populations evolve over time. In such landscapes, every point in space represents a particular genotype, while the height of the point reflects the fitness of the genotype. Therefore, evolution can be thought of as a walk of the evolving population along ridges of high fitness. Until recently, there were no methods to obtain enough data to study the shape of natural fitness landscapes but in the current paper, thanks to a novel experimental approach, researchers has been able to look at the fitness landscape of the whole protein.
To measure the brightness of every mutant, researchers expressed mutant genes in the bacterium Escherichia coli, and then used a cell sorter to sort bacteria according to their brightness. Sequencing of DNA from each tube allowed scientists to connect the brightness of mutant proteins to the underlying genotypes.
"I would say that this is the first experimental illustration of the concept of fitness landscapes that was invented 85 years ago," Sarkisyan said. "After measuring brightness of 50,000 mutants we were able to finally have a look at what these landscapes look like".
Scientist found that only every fourth amino acid change does not damage the protein, while most mutations negatively affect protein function. Moreover, if a slightly damaging mutation is already present in the gene, the negative effect of the following mutations will be strengthened leading to the non-functional protein much faster than if mutational effects are independent.
The strong interactions between mutations that the authors found in the fluorescent protein might be important piece to other areas of science. One of the key challenges of the modern medical genetics is the understanding of diseases with complex genetic component, like cardiovascular diseases. The prevalence of interactions between mutations and the influence of these interactions on human health is still an unsolved issue in human genetics. The new work on the fluorescent protein gives geneticists grounds to start looking for such interactions in complex multigene diseases. The paper has been published in Nature magazine.