nounIntermediate
Definition
Mirror-image (right-handed) stereoisomer of an amino acid; rare in nature but widely used in peptide drug design to confer protease resistance and improve metabolic stability.
Detailed Explanation
Almost all amino acids in biology are L-form (left-handed). D-amino acids are their mirror images — chemically identical but spatially reversed, like left and right hands. Because proteases evolved to recognize L-amino acid substrates, incorporating D-amino acids into a peptide at key positions makes it 'invisible' to digestive and serum proteases, dramatically extending half-life. D-amino acids also induce β-turns in peptide chains, useful for conformational control in cyclic peptide design. D-amino acids do occur naturally in some bacterial cell walls (D-Ala, D-Glu in peptidoglycan), in some marine peptides, and in aged human tissues.
Key Facts
- Almost all amino acids in biology are L-form (left-handed)
- D-amino acids are their mirror images — chemically identical but spatially reversed, like left and right hands
- Because proteases evolved to recognize L-amino acid substrates, incorporating D-amino acids into a peptide at key positions makes it 'invisible' to digestive and serum proteases, dramatically extending half-life
- D-amino acids also induce β-turns in peptide chains, useful for conformational control in cyclic peptide design
- D-amino acids do occur naturally in some bacterial cell walls (D-Ala, D-Glu in peptidoglycan), in some marine peptides, and in aged human tissues
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