Why are all proteins left-handed?

Patrick Wang

Patrick Wang

Expert of Peptides | Ask me anything about Peptides | Sales Manager at AHB Lab
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The Enigmatic Bias in the Building Blocks of Life

The foundation of life exhibits a fascinating bias that puzzles scientists: almost all proteins are made of amino acids that are “left-handed.” This preference exists despite both mirror-image forms of amino acids, resembling left and right-handed gloves, being theoretically equally prevalent in the early days of Earth. The prevailing question has been: what influenced the primordial world to favor left-handed amino acids, setting a precedent that has been maintained throughout the evolution of life?

protein

 

A Novel Explanation from Recent Research

A breakthrough study conducted by a team of U.S. researchers offers a compelling explanation for this bias. Published in the prestigious journal Nature, their research meticulously analyzed the formation rates of amino acid pairs, known as dipeptides, revealing mechanisms that preferentially promote dipeptides composed of amino acids with matching handedness. This discovery could potentially extend to explain the uniform orientation in larger molecules like proteins, and intriguingly, the opposite bias observed in RNA and DNA molecules, which predominantly consist of right-handed sugars.

Insights from Experiments and Theories

The quest to understand life’s chirality, or directional bias, has led to various theories over the years. Some speculate that life’s building blocks may have been influenced by external forces, such as polarized light from space or Earth’s magnetic fields. However, these theories lacked a mechanism for perpetuating the initial bias.

Recent advancements by Matthew Powner and his team at University College London have shed light on this mystery. They explored sulfur-based molecules, likely present on early Earth, that facilitate the formation of dipeptides in water. This process, compatible with all amino acids found in living organisms, presents a plausible pathway for the initial protein formation.

Building on this foundation, Donna Blackmond’s team at Scripps Research took the investigation further. They discovered that certain sulfur compounds, when acting as catalysts, showed a preference in forming dipeptides with mixed chirality. Initially, this seemed to complicate the understanding of life’s chirality. However, deeper analysis revealed a domino effect: a slight initial bias towards one form of amino acids could lead to a significant predominance of homochiral (same-handed) dipeptides.

The Domino Effect and Its Implications

The process unfolds as heterochiral (mixed-handed) dipeptides form more rapidly, gradually leading to a surplus of the initially more abundant form of amino acids. This imbalance increases the likelihood of forming homochiral dipeptides. Moreover, the researchers observed that heterochiral dipeptides tend to precipitate out of solution faster than their homochiral counterparts, further skewing the balance towards a single chirality based on the initial mix.

This mechanism, though demonstrated with dipeptides, suggests a broader principle that could apply to the formation of longer peptide chains and potentially to the chirality observed in genetic molecules like RNA.

 

Toward a Unified Theory of Life’s Chirality

The implications of this research extend beyond the molecular level, potentially offering insights into one of the fundamental aspects of life’s origin. The “left-handedness” of amino acids and the opposite bias in the sugars of RNA and DNA might stem from similar statistical and chemical biases, a hypothesis that future research will continue to explore.

This groundbreaking study not only advances our understanding of life’s molecular asymmetry but also opens new avenues for investigating the origin of life on Earth. As researchers delve deeper into the mechanisms behind life’s chirality, the mystery of why life prefers one handedness over the other becomes less enigmatic, bringing us closer to understanding the very essence of our existence.

 

Understanding Peptide Structure: Orientation, Bonds, and Biological Function

The structure of a peptide is a critical aspect of its function and biological activity, intricately determined by the sequence and orientation of its amino acids. Peptides are formed through the dehydration synthesis between the amino group of one amino acid and the carboxyl group of another, creating a covalent bond known as a peptide bond. This process repeats to form long chains of amino acids, which can fold into specific three-dimensional shapes essential for their biological roles. The sequence from the N-terminal (amino group) to the C-terminal (carboxyl group) end not only dictates the peptide’s structure but also influences its ability to interact with other molecules. The physical properties and reactivity of the side chains of the constituent amino acids further contribute to the peptide’s overall shape and function, allowing for a diverse range of biological activities and functions, from signaling to catalytic roles within cells. Understanding the structure of peptides, including their spatial configuration and folding patterns, is fundamental in biochemistry and molecular biology, providing insights into protein function, enzyme activity, and the molecular basis of diseases.

At AHB Lab, we’re not just leaders in peptide synthesis; we’re at the heart of pioneering biotechnology exploration. Our focus goes beyond mastering peptide production to embody a vision that drives innovation across the biotech landscape. We are committed to exploring the depths of peptide structure and function, uncovering the molecular mysteries that hold the key to groundbreaking health solutions. By aligning with the latest in scientific research and technological advancements, AHB Lab is dedicated to spearheading developments that not only enhance our understanding of peptides but also pave the way for revolutionary biotech applications. Join our quest as we forge new paths in science and contribute to shaping the future of biotechnology with our unwavering commitment to excellence and innovation.

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