Glycopeptide incorporated into

D-Alanine is found in bacterial cell wall peptidogly-can. l-Alanine is converted to D-alanine by a racemase that contains pyridoxal phosphate as a cofactor. The racemiza-tion is followed by the formation of a D-alanyl-D-alanine dipeptide, which is accompanied by the conversion of ATP to ADP. The dipeptide is subsequently incorporated into the glycopeptide (see fig. 16.16). 

Vegad, H., Gray, C., Somers, P., and Dutta, A. (1997) Glycosylation of Fmoc amino acids preparation of mono- and di-glycosylated derivatives and their incorporation into Arg-Gly-Asp(RGD)-containing glycopeptides. J. Am. Chem. Soc. Perkin Trans I., 1429-1441. 

Otvos Jr. L, Urge L, Hollosi M, Wroblewsky K et al., Automated solid-phase synthesis of glycopeptides, Incorporation of unprotected mono- and disaccharide units of N-glycoprotein Antennae into T cell epitopic peptides, Tetrahedron Letters, 31 5889-92, 1993. 

One example is the bacterial response to the challenge presented by the glycopeptide vancomycin - the bacteria simply altered the target. As noted by the authors, vancomycin is a clamp that binds to the D-alanine-D-alanine terminus of the peptide stem of a cell wall precursor, thereby preventing its incorporation into the cell... 

---