Synthesis of Lipid II Substrate for Peptidoglycan Glycosyltransferease and Exploration of the Transition-State Inhibitors
Date Issued
2010
Date
2010
Author(s)
Wang, Jen-Tsung
Abstract
After decades of extensively using antibiotics, many bacterial pathogens have mutated to resist antibiotics, and become an increasingly serious medical problem of human and animal. The rise of antimicrobial resistance problem has promoted the research efforts to understand the detailed structures and mechanistic information on bacterial peptidoglycan glycosyltransferases (PGTs) in order to design new antimicrobial agents. Peptidoglycan, a major component of bacterial cell wall, is formed by transglycosylation and transpeptidation of Lipid II substrate to a mesh-like polymer, which provides strength and rigidity to maintain the shape against variable internal osmotic shock. PGTs are attractive targets because no equivalent exists in the mammalian cell. PGTs are located on the outer surface of membrane with high homology in various strains including those mutated to exhibit resistance against the current antibiotics.
Our research is to target the specific enzyme, transglycosylase (TGase) in peptidoglycan biosynthesis pathway, through chemical synthesis to prepare natural Lipid II substrate and derivatives. Our HPLC-based TGase fluorescence assay indicated that the truncated Lipid II lacking tetrapeptide moiety was still a substrate in the tranglycosylation process, nevertheless, with decreased substrate–enzyme binding affinity.
We also designed and synthesized some possible TGase inhibitors, using a 3-hydroxyl pyrrolidine as the core structure with various substituents at the 6- position. The derivatives of phosphoglycerate motif in moenomycin, the unique natural inhibitor of TGase, were adopted to mimic the important pyrophosphate binding site of Lipid II. Several 3-hydroxyl pyrrolidine core and phosphoglycerate lipid moieties linked to afford the potential TGase inhibitors. In physiological conditions, the protonated pyrrolidine structure has the geometry and charge distribution similar to an oxocarbenium ion, which is a necessary element of transition-state in the process of transglycosylation.
By the HPLC-based TGase fluorescence assay, compounds JMF2809 and JMF2805 presented some TGase inhibition, where most of other compounds were inactive. By comparison of chemical structures, the active compounds likely compete the pyrophosphate lipid portion of Lipid II in the TGase binding site. Modification of these active compounds may eventually lead to efficient inhibitors of TGase.
Subjects
cell wall
peptidoglycan glycosyltransferease
transglycosylase
antibiotic
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-99-D95223020-1.pdf
Size
23.32 KB
Format
Adobe PDF
Checksum
(MD5):9a3fcee9f4fecb24c4bc4b6128b05091