Shenshen Lai and colleagues from the University of British Columbia report results from a study of protein kinases in eukaryotes (A eukaryote is any organism whose cells contain a nucleus and other organelles enclosed within membranes.
Protein kinases play a pivotal role in communicating intracellular signals in eukaryotes. The family of eukaryotic protein kinases (ePKs) comprises of at least 568 human members, which accounts for more than 2% of protein coding genes of the entire human genome. These kinases are highly conserved both their primary amino acid sequences in the 3D structures of their catalytic domains. Because of the central regulatory roles the high conservation of the ePKs, the ancestry of these enzymes has become an important question in the study of the evolution eukaryotic organisms.
The ePKs and ChPK are responsible for amongst other things the construction of the cell membrane (which allow the development of organelles including the nucleus to develop) and communication between organelles within the cell. They are likely responsible for the evolution and success of organisms larger than prokaryotic organisms like for example bacteria which lack a nucleus and membrane bounded organelles. Without the early horizontal transfer and preservation of GlnRS life as we know it would likely not exist. GlnRS is found in all complex organisms including plants and animals.
Eukaryotic life is believed to have evolved between 1.7 to 2.7 billion years ago and no living representatives of the earliest eukaryotes survive today. Consequently, the actual origin of protein kinases is difficult to establish with a high degree of confidence.
They conclude that ePKs and ChPKs in eukaryotes evolved from an ancient common mRNA source (possibly at the commencement of life on earth – or at least very early). While these proteins are highly degenerate this team has identified two class-I aminoacyl-tRNA synthetases with high similarities to consensus amino acid sequences of human protein-serine/threonine kinases suggesting that horizontal transfer early in evolution gave rise to many contemporary genes.
This research provides solid argument for the continuity of life on early for much of the last 3 billion years and our genetic relationship to the earliest lifeforms on this planet.