How life got moving: Nature’s ingenious motor

Research led by the University of Auckland has cast more light on the origin of one of nature’s first motors, which evolved 3.5 billion to 4 billion years ago for bacteria to swim.

Scientists have created the most comprehensive picture yet of the evolution of bacterial stators, proteins with roles similar to pistons in a car engine, says Dr Caroline Puente-Lelievre, of the School of Biological Sciences.

“Movement is essential to life, from microbes to the largest animals,” says Puente-Lelievre. “Within our cells, constant molecular motion is what keeps us alive. We’re unravelling the story of how life first got moving.”

Bacteria are among our earliest life forms, dating from when the Earth was wildly volcanic and bombarded by meteorites, the sky orange and the seas green because of the dominant chemicals.

In this harsh environment, bacteria developed as single cell beings, and a nifty nanomachine evolved to power their swimming. 

The scientists were focused on one key part of the nanomachine: "stator proteins", which sit in the bacterial cell wall, transforming charged particles (ions) into torque.

The research in collaboration with UNSW Sydney and University of Wisconsin Madison was made possible by DeepMind AI’s revolutionary AlphaFold breakthrough in 2020 predicting the 3D folded shapes of proteins.

Stators  power a rotor, which spins the flagellum – a long tail that pushes the cell through liquid like a microscopic propeller. (Flagellum is Latin for whip, here alluding to the whip-like movements of the tail.)

The scientists believe bacterial stators likely evolved from molecules called ion transporter proteins, commonplace in bacterial cell membranes. Their research was published in the journal mBio.

To investigate stators, the scientists parsed genomic data from over 200 bacterial genomes, built evolutionary trees with advanced computational tools, modelled 3D protein structures, and conducted hands-on lab experiments.

The 3D shape of each protein was crucial because shape is critical to function.

“We predicted the sequences and structures of ancestral proteins that existed millions or billions of years ago and may no longer exist,” says Puente-Lelievre.

A stator is typically made up of five identical versions of a protein called MotA and two identical versions of a protein called MotB.

These “motor proteins” derived from an ancient two-protein system that evolved a variety of other functions, says Dr Nick Matzke, the senior researcher from the University of Auckland.

“This supports the idea that complex machines evolve by coopting simpler machines with simpler functions."

Much as the dinosaur ancestors of birds probably evolved protofeathers to keep warm, later redeploying them for gliding or flying, ancient bacteria likely put an ion flow tool to a new use, he says.

What began as a simple mechanism for moving ions across a membrane became one of nature’s most enduring engines.

In the research, Puente-Lelievre and her colleagues compared 3D protein structures to identify key differences between similar proteins and the traits unique to the stators, such as torque generating regions.

“Finally, we performed functional assays in the lab,” she says. “We took E. coli bacteria that lacked the torque-generating interface and found that none of them could swim, confirming that this specific region is essential for movement in this group of bacteria.”

Despite billions of years of evolution, the essential features of these tiny engines are little changed and remain as relevant as ever.

“We live in a remarkable era for structural biology and microbiology, where new sequences are discovered daily and tools like AlphaFold let us near instantly explore possible protein structures,” says Associate Professor Matthew Baker of UNSW Sydney.

“In this study, we cast a wide net across species to find stator-like proteins, revealing what they share, how they differ, and how these engines may have evolved throughout history.”

The research was funded by Human Frontier Science Program, University of Auckland's Faculty of Science, John Templeton Foundation and the Alfred P. Sloan Foundation.

Co-authors were Pietro Ridone, Dr Jordan Douglas, Kaustubh Amritkar, and Assistant Professor Betül Kaçar.