Scientists Successfully Remove Amino Acid From Genetic Code

Researchers at Columbia University, the Massachusetts Institute of Technology, and Harvard University have successfully engineered a strain of Escherichia coli to function with a reduced genetic code – specifically, one that doesn’t require the amino acid isoleucine. This represents an early step in understanding how life might have functioned with a simpler biochemical toolkit and could pave the way for designing organisms with novel capabilities.

The genetic code, fundamental to all known life, typically utilizes 20 amino acids to build proteins. Scientists have long theorized that early life forms may have relied on a smaller set of these building blocks. This new research, published in Science, provides experimental evidence supporting that hypothesis. The team used artificial intelligence (AI) to redesign ribosomal proteins – essential components of protein synthesis – to function effectively without isoleucine.

Rewriting Life’s Alphabet

The project’s core aim wasn’t simply to remove an amino acid, but to explore the limits of life’s chemistry and gain insight into its origins. “The underlying question that we seek to ask is what early life looks like,” explained Harris H. Wang, a professor of systems biology at Columbia University Irving Medical Center and senior author of the study. Researchers believe that all current life descended from a single-celled ancestor over four billion years ago, but simpler life forms may have existed before it.

While previous work has focused on expanding the genetic code to incorporate new, non-natural amino acids, this research takes a different approach – subtraction. Most attempts to alter the genetic code have been hampered by the disruption of protein function when even minor changes are made to amino acid sequences. The team overcame this challenge by leveraging advances in AI-driven protein design, which allowed them to predict and compensate for the effects of removing isoleucine.

Isoleucine is one of three structurally similar amino acids – alongside leucine and valine – all possessing a branched carbon-hydrogen structure. The researchers focused on isoleucine because its removal presented a manageable first step in simplifying the genetic code. They didn’t create a fully 19-amino-acid organism; rather, they engineered the ribosome itself to function without requiring isoleucine in its construction.

AI’s Role in Simplifying Complexity

The success of this project hinges on the increasing sophistication of AI tools for protein design. Previously, redesigning proteins to function with fewer amino acids was considered impractical. However, recent advancements have made it possible to accurately predict how changes to amino acid sequences will affect protein structure and function. This allowed the researchers to identify and create modified ribosomal proteins that maintained their essential roles despite the absence of isoleucine.

The engineered E. Coli strain was able to survive and function, demonstrating that at least a portion of life’s core machinery can tolerate a simplified amino acid palette. This finding suggests that early life forms may have indeed relied on a more limited set of building blocks, and that the current 20-amino-acid code represents a later evolutionary development.

Implications for Synthetic Biology

Beyond shedding light on the origins of life, this research has significant implications for the field of synthetic biology. The ability to manipulate the genetic code opens up possibilities for creating organisms with entirely new functionalities. By streamlining the code, scientists could potentially design cells with enhanced efficiency, novel metabolic pathways, or resistance to viruses.

As Julius Fredens, a synthetic biologist at the National University of Singapore, noted, the work is “very exciting” and offers “a blueprint for engineering cells with capabilities beyond those found in nature.” The researchers acknowledge that further work is needed to explore the limits of this approach and to determine whether organisms can be engineered to function entirely without isoleucine throughout their genomes. However, this study represents a significant step towards rewriting the fundamental rules of life and harnessing the power of synthetic biology.