Scientists identify the proteins that allowed vertebrates to evolve. Most animal species are vertebrates, including mammals, birds, fish, reptiles, and amphibians. Scientists at Kyoto University’s Institute for Integrated Cell-Material Sciences (iCeMS) have spent nearly four decades investigating how vertebrates evolved, and recently discovered a family of proteins that played a very important role. Scientists identify the proteins that allowed vertebrates to evolve
The study suggests that one transporter protein in particular, ABCA1, was critical for regulating the signals involved in cell proliferation, differentiation, and migration. These processes were required for vertebrates to develop into more complex organisms.
The ATP-binding cassette proteins (ABC) are very similar across species, including in bacteria, plants, and animals. Different types of ABC proteins have different responsibilities, such as transporting nutrients into cells, exporting toxic compounds, and regulating lipid concentrations within cell membranes. Scientists identify the proteins that allowed vertebrates to evolve
Kazumitsu Ueda is a cellular biochemist at iCeMS who has studied human ABC proteins ever since he and his colleagues identified the first eukaryote ABC protein gene 35 years ago.
“We believe ABC proteins must have played important roles in evolution,” said Ueda. “By transporting lipids, they enabled plants and animals to thrive on land by protecting them from water loss and pathogen infection. They are also assumed to have accelerated vertebrate evolution by allowing cholesterol to function as an intra-membrane signalling molecule.”
Some of the earliest organisms on Earth were likely formed of DNA and proteins surrounded by a leaky lipid membrane. As the organisms evolved, their membranes were strengthened to protect them from the external environment. What this means is that only those organisms that gained special ABC transporters – capable of carrying nutrients across the membrane – would have survived.
ABC proteins also produced an outer membrane that protected cells from external stresses and removed harmful substances from inside.
Ueda and his team analyzed the roles of ABCA1, gaining deeper insight into how it regulates cholesterol. In particular, they found that ABCA1 exports cellular phospholipids and cholesterol outside the cell for generating high-density lipoproteins, or “good cholesterol.”
According to the experts, ABCA1 constantly flops cholesterol from the cell membrane’s inner leaflet to its outer leaflet, maintaining a lower concentration on the inner side. This process is temporarily suppressed when the cell is exposed to an external stimulus, like a growth hormone, which leads to an accumulation of cholesterol in the inner leaflet. As a result, proteins are recruited to the cell membrane.
The researchers believe that ABCA1 allowed vertebrates to evolve complicated biological processes and sophisticated bodies.
“ABCA1 is very unique and its functions surprised us,” said Ueda. “Cholesterol’s role was thought to focus mainly on physically strengthening the cell membrane and reducing its permeability to ions. Our research suggests it played a more important role in vertebrates, accelerating their evolution.”
The study is published in the journal FEBS Letters.