Dresidues

Dresidues, or D-residues, refer to residues in polymers, typically amino acid residues, that have the D-configuration as opposed to the more common L-configuration in biology. In peptides and proteins, amino acids are usually L-stereoisomers, but D-residues occur in certain biological contexts and synthetic systems.

Natural occurrence is most notable in bacterial cell walls, where D-alanine and D-glutamate are incorporated into peptidoglycan and contribute to structural rigidity and resistance to certain enzymes. D-residues also appear in some non-ribosomal peptides produced by specialized enzymes, where the inclusion of D-amino acids can influence folding, stability, and bioactivity. In eukaryotic proteins, D-residues are comparatively rare and often arise through post-translational racemization or aging-related processes.

Formation mechanisms include enzymatic racemization by specific racemases that convert L- to D-amino acids, as well as non-enzymatic racemization under conditions of time, temperature, or oxidative stress. These processes can alter protein conformation and function and may impact proteolytic susceptibility.

Detection and analysis rely on chiral separation techniques such as chiral chromatography or derivatization methods followed by mass spectrometry, which distinguish D- from L-residues.

Applications and significance include the role of D-residues in bacterial cell-wall biology, where they influence pathogenicity and antibiotic interactions, and the use of D-amino acids in biotechnology and drug design to create more stable, protease-resistant peptides and materials. See also D-amino acids, L-amino acids, and racemization.