Classic Style Guide,D-Alanyl-D-alanine is a dipeptide

D-Ala-D-Ala, also known by its CAS number 923-16-0, is a fascinating dipeptide with profound implications in microbiology, biochemistry, and pharmaceutical research. Composed of two D-alanine amino acid residues linked by a peptide bond, this peptide is a non-proteinogenic amino acid, meaning it deviates from the standard amino acids found in proteins. Its significance lies primarily in its fundamental role within the bacterial peptidoglycan structure, a critical component of the bacterial cell wall.

The D-Ala-D-Ala moiety forms the carboxy-terminal dipeptide sequence (D-Ala-D-Ala), serving as the crucial terminus moiety of bacterial peptidoglycans. This specific arrangement is essential for the structural integrity and survival of many bacteria. The synthesis of this vital component is orchestrated by enzymes such as D-alanyl-D-alanine ligase, also referred to as D-Ala:D-Ala ligase. These enzymes belong to the ATP-grasp ligases superfamily, specifically those that catalyze the formation of carbon-nitrogen bonds, acting as acid-D-amino-acid ligases or peptidesynthases. In some bacteria, the D-Ala-D-Ala structure is further modified by enzymes like D-alanyl-D-alanine carboxypeptidase, which removes C-terminal D-alanyl residues from sugar-peptide cell wall precursors. This enzymatic activity plays a role in the dynamic remodeling of the cell wall during bacterial growth and division.

Beyond its structural role, D-Ala-D-Ala is a biologically significant molecule that has found substantial utility in scientific research. Its unique properties make it valuable for affinity chromatography and binding mechanism studies of antibiotics, particularly those that target bacterial cell wall synthesis. For instance, the interaction of antibiotics like vancomycin with the D-Ala-D-Ala terminus is a well-studied phenomenon, offering insights into antibiotic resistance mechanisms. In this context, enzymes like VanX, a bacterial d-alanyl-d-alanine dipeptidase, play a crucial role in conferring vancomycin resistance. VanX hydrolyzes D-Ala-D-Ala, preventing the antibiotic from binding effectively to its target. The study of D-Ala-D-Ala ligases capable of ester formation has also been pivotal in understanding resistance mechanisms, with some ligases showing preferential catalytic efficiency for forming D-Ala-D-Lac instead of D-Ala-D-Ala.

The scientific community actively researches the synthesis and function of D-Ala-D-Ala. Studies have explored the enzymology of D-alanyl-D-alanine ligase and its control mechanisms. The dipeptide product D-Ala-D-Ala is often observed in structural studies of these enzymes, such as the solved structures of EcDdlB containing either ADP or ATP, highlighting the energy-dependent nature of its formation.

The broader implications of D-Ala-D-Ala extend to the development of novel therapeutic agents and the understanding of biological processes. Researchers are investigating D-Ala-ended peptidoglycan precursors for their potential immunomodulatory abilities. Furthermore, the study of cyclic D,L-α-peptides, which are proteolytically stable and easy to synthesize, offers a vast membrane-active sequence space that can be derived from amino acids like alanine. While not directly analogous to the bacterial cell wall component, the exploration of D-alanine in other biological contexts, such as the D-alanine-containing peptide dermorphin isolated from frog skin with potent opiate-like activity, underscores the diverse roles non-standard amino acids can play.

Commercially, D-Ala-D-Ala is available from various scientific suppliers, often identified by its CAS number 923-16-0 and synonyms like D,D-Dialanine or D-Alanine, D-alanyl-. Its availability facilitates ongoing research into its biochemical functions, enzymatic interactions, and potential applications. The chemical structure, C6H12N2O3, and its identification as a dipeptide comprising D-alanine with a D-alanyl residue attached to the alpha-nitrogen, are fundamental to its characterization.

In summary, D-Ala-D-Ala is far more than a simple dipeptide. It is a cornerstone of bacterial cell wall architecture, a critical target for antibiotics, and a valuable tool in biochemical and pharmacological research. Its presence, synthesis, and modification by specific enzymes are central to understanding bacterial survival, antibiotic efficacy, and the broader landscape of peptide chemistry.