A broader context for understanding amino acid alphabet optimality.

Area of Science:

• Biochemistry
• Astrobiology
• Origin of Life Studies

Background:

• Prior research suggests unique physicochemical properties of the 20 genetically encoded amino acids.
• Variations in methodologies across studies necessitate a consolidated framework.

Purpose of the Study:

• To unify and clarify the unusual features of the genetically encoded amino acid set.
• To compare the distribution of these amino acids against random samples of plausible alternatives.

Main Methods:

• Utilized quantitative descriptors for size, charge (pKa), and hydrophobicity.
• Compared the distribution of the 20 standard amino acids with random samples of plausible L-α-amino acids.
• Analyzed both the full set and prebiotically plausible subsets of amino acids.

Main Results:

• The standard 20 amino acids exhibit an unusually broad range in volume and even distribution in hydrophobicity.
• Exceptional range and evenness in charge (pKa) were observed for full structures, not sidechains.
• These remarkable features are less pronounced when considering only prebiotically plausible amino acids.

Conclusions:

• The unusual physicochemical properties of the genetically encoded amino acids are robust, especially for volume and hydrophobicity.
• The findings challenge prior interpretations regarding the role of amino acid sidechains in protein sequences.
• Further research is suggested to explore optimality theory in the context of amino acid selection.