Beta-turn-driven early evolution: the genetic code and biosynthetic pathways.

The physicochemical properties of beta-turns suggest their biological importance prior to the formation of the genetic code. These properties include ones potentially affecting the preference for either L- or D-amino acids. The abundance of certain amino acids in beta-turns is correlated with their assignment to a small, well-defined part of the genetic code and with their role as metabolic precursors for other amino acids. It is proposed that in the prebiotic environment, beta-turns became objects of selection that influenced the evolution of the genetic code and biosynthetic pathways for amino acids.