Changes

Once the basic heptapeptide scaffold is assembled, further post translational modifications take place on the molecule. First, residues 2 and 4, 4 and 6, and 5 and 7, undergo oxidative crosslinking, become covalently bonded to each other, forming the highly rigid, dome-like structure of vancomycin. This conformation is what gives vancomycin its high affinity for forming hydrogen-bonds with its target - the N-acyl-D-Ala-D-Ala termini of the peptidoglycan precursors in bacteria. The molecule in this state is biologically active and is termed the aglycone backbone of vancomycin<ref name="Reynolds"> Reynolds, P.E. (1989). Structure, Biochemistry and Mechanism of Action of Glycopeptide Antibiotics. European Journal of Clinical Microbiolo1 and Infectious Diseases, 8(11), 943-950. https://doi.org/10.1007/BF01967563 </ref> . Finally, the Leucine is methylated to N-methyleucine, and two successive glycosylations on the ph2late of the HPG residue give the finished vancomycin molecule. These further modifications are not essential for the antibiotic functionality of vancomycin though they do allow for stronger interactions with the target. <ref name="Nolan" />

Vancomycin kills and prevents the growth of gram-positive bacteria by inhibiting the cell-wall synthesis of these bacteria <ref name="Reynolds" />. The cell walls of gram-positive bacteria are comprised of several layers of peptidoglycan, a mesh-like polymer made up of sugars and amino acids. It is this layer that provides the necessary mechanical support for bacteria to be able to withstand fluctuations in osmotic pressures in excess of 5-15 atm without lysing (rupturing)<ref name="Kahne"> Kahne, D., Leimkuhler, C., Lu, W. & Walsh, C. (2005). Glycopeptide and Lipoglycopeptide Antibiotics. Chemical Reviews, 105, 425-448. </ref> .