D-Ala-D-Ala-OH

An enzyme-linked immunosorbent assay (ELISA) was developed for the quantitative measurement of IgG antibodies to the immunodominant R-D-Ala-D-Ala-OH determinant of peptidoglycan. Synthetic peptides R-D-Ala-D-Ala-OH, revealing structural analogy with the C-terminal sequence of the antigenic determinant H-L-Ala-D-Glu(L-Lys-D-Ala-D-Ala-OH)-NH2 of peptidoglycan, were coupled covalently to albumin via their amino groups. The resulting peptidyl proteins were employed as an antigen in an ELISA for the specific detection of human IgG antibodies against the C-terminal R-D-Ala-D-Ala-OH moiety of H-L-Ala-D-Glu(L-Lys-D-Ala-D-Ala-OH)-NH2. Antigenic specificity was proved by comparing the high binding to albumin-(D-Ala-D-Ala-D-Ala-OH)9 with a lack of binding to albumin-(L-Ala-L-Ala-L-Ala-OH)13 and by appropriate inhibition studies of the ELISA. IgG, totally free from IgA and IgM, was isolated from reference serum 004, and the particular specificity was entirely found in this fraction. Quantification of the ELISA was effected by affinity chromatography. Isolated IgG was applied to an affinity column of Sepharose-[albumin-(D-Ala-D-Ala-D-Ala-OH)9]n, unbound IgG was eluted with phosphate-buffered saline and specific IgG against the C-terminal R-D-Ala-D-Ala-OH moiety of H-L-Ala-D-Glu(L-Lys-D-Ala-D-Ala-OH)-NH2 was eluted with 6 M guanidinium chloride.

Glycopeptide antibiotics are widely used in the treatment of infections caused by Gram-positive bacteria. They inhibit the biosynthesis of the bacterial cell wall through binding to the D-alanyl-D-alanine (D-Ala-D-Ala) terminal peptide of the peptidoglycan precursor. Taking advantage of this highly specific interaction, we developed a direct fluorescence polarization based method for the detection of glycopeptide antibiotics. Briefly, we labeled the acetylated tripeptide Ac-L-Lys-D-Ala-D-Ala-OH with a fluorophore to create a peptide probe. Using three glycopeptide antibiotics, vancomycin, teicoplanin, and telavancin, as model compounds, we demonstrated that the fluorescence polarization of the peptide probe increased upon binding to antibiotics in a concentration dependent manner. The dissociation constants (K(d)) between the peptide probes and the antibiotics were consistent with those reported between free d-Ala-d-Ala and the antibiotics in the literature. The assay is highly reproducible and selective toward glycopeptide antibiotics. Its detection limit and work concentration range are 0.5 microM and 0.5-4 microM for vancomycin, 0.25 microM and 0.25-2 microM for teicoplanin, and 1 microM and 1-8 microM for telavancin. Furthermore, we compared our assay in parallel with a commercial fluorescence polarization immunoassay (FPIA) kit in detecting teicoplanin spiked in human blood samples. The accuracy and precision of the two methods are comparable. We expect our assay to be useful in both research and clinical laboratories.

The fraction of administered antibiotics that reach the cecum and colon causes dysbiosis of the gut microbiome, resulting in various diseases. Protection of the gut microbiome from antibiotics using antibiotic adsorbents in the cecum and colon is a promising method to overcome this issue. Previously, activated charcoal (AC) has been reported to protect the gut microbiome of host animals. AC is an adsorbent that is widely used to capture toxic compounds and overdosed drugs in the gastrointestinal tract. The specificity of adsorbents for antibiotics is critical to avoid the risk of unexpected side effects caused by nonspecific adsorption of biological compounds in the intestinal fluid, such as bile acids and essential micronutrients. Here, we have developed specific adsorbents for vancomycin (VCM), which is known to cause gut dysbiosis. The adsorbents were composed of polyethyleneglycol-based microparticles (MPs) in which a specific ligand for VCM, D-Ala-D-Ala-OH, was attached via dendrons of D-lysine to raise the content of the ligand in the MPs. The MPs successfully protected Staphylococcus lentus from VCM in vitro because of the adsorption of VCM in the culture media. Pre-administration of MPs to mice reduced the amount of free VCM in the feces to an undetectable level. This treatment minimized the effect of VCM on gut microbiota and provided protection against Clostridioides difficile infection after oral challenge with spores.