Artwork showing mitochondria. Credit: Andrzej Wojcicki/SPL/Getty Images
Molecular biologists have discovered how ancient bacteria gradually evolved into mitochondria in eukaryotic cells1. Those eukaryotic cells ultimately gave rise to all complex life forms, such as plants and animals.
The researchers identified two key changes in the protein synthesis and surveillance machineries of the eukaryotic cells that resulted in the successful transition from bacteria to mitochondria.
Amino acids come in two different forms – L and D. L-amino acids are predominantly used to make proteins in cells. From bacteria to mammals, cells use D-aminoacyl-tRNA deacylase (DTD), a proofreading enzyme that only allows L-amino acids, to prevent D-amino acids being incorporated into proteins.
The research team, led by Rajan Sankaranarayanan at the Centre for Cellular and Molecular Biology (CCMB) in Hyderabad, found that the bacterial DTD had undergone a change that was compatible for use in eukaryotic cells. They also found a change in the discriminator element for mitochondrial transfer RNA (tRNA) that shuttles glycine, an essential amino acid for making a protein.
Of the 1,000 proteins identified in mitochondria, 40% are of bacterial origin. To trace back mitochondria’s origin, the scientists did experiments with Jakobida, the earliest known, tiny free-living organisms that retain a bacteria-like mitochondrial genome.
The team detected the intermediate state of the tRNA discriminator-code transition in the mitochondrial genome of Jakobida. They believe this probably happened during the bacteria-to-mitochondria transition.
The researchers says their findings will help to increase understanding of the complex evolutionary history of mitochondria.
