Functional and Structural Analysis of a Key Region of the Cell Wall Inhibitor Moenomycin

Abstract

Moenomycin A (MmA) belongs to a family of natural products that inhibit peptidoglycan biosynthesis by binding to the peptidoglycan glycosyltransferases (PGTs), the enzymes that make the glycan chains of peptidoglycan. MmA is remarkably potent, but its clinical utility has been hampered by poor physicochemical properties. Moenomycin contains three structurally distinct regions: a pentasaccharide, a phosphoglycerate, and a C25 isoprenyl (moenocinyl) lipid tail that gives the molecule its name. The phosphoglycerate moiety links the pentasaccharide to the moenocinyl chain. This moiety contains two negatively charged groups, a phosphoryl group and a carboxylate. Both the phosphoryl group and the carboxylate have previously been implicated in target binding but the role of the carboxylate has not been explored in detail. Here we report the synthesis of six MmA analogs designed to probe the importance of the phosphoglycerate. These analogs were evaluated for antibacterial and enzyme inhibitory activity; the specific contacts between the phosphoglycerate and the protein target were assessed by X-ray crystallography in conjunction with molecular modeling. Both the phosphoryl group and the carboxylate of the phosphoglycerate chain play roles in target binding. The negative charge of the carboxylate, and not its specific structure, appears to be the critical feature in binding since replacing it with a negatively charged acylsulfonamide group produces a more active compound than replacing it with the isosteric amide. Analysis of the ligand-protein contacts suggests that the carboxylate makes a critical contact with an invariant lysine in the active site. The reported work provides information and validated computational methods critical for the design of analogs based on moenomycin scaffolds.

Crystal structure of Staphylococcus aureus transglycosylase in complex with a lipid II analog and elucidation of peptidoglycan synthesis mechanism

“…4A). The residues (G130, Q137, K140, N141, R148, and N224) around the conserved motifs II, III, and IV are important for binding lipid II or the growing glycan chain to the glycosyl donor site S2 (12)(13)(14)(15)(19)(20)(21). The loop from G130 to S132 is used to stabilize the substrate at both S1 and S2.…”

Moenomycin family antibiotics: chemical synthesis, biosynthesis, and biological activity

“…The sulfoxide glycosylation method was used to make the EF glycosidic bond, and the preconstructed disaccharide was attached to a photolinker resin. After derivatization of the disaccharides and their release from the resin, simplified phospholipid moieties (some of which lacked the carboxylate at the phospho-end, which is an essential part of moenomycin pharmacophore8, 74 were attached. A disaccharide library of 1300 members was created and several compounds (for example, representative member 32 ) were identified that inhibited bacterial growth at low microgram concentrations 75.…”

Tuning the Moenomycin Pharmacophore To Enable Discovery of Bacterial Cell Wall Synthesis Inhibitors

“…11 It was also reported that a lipid side chain of at least 10 carbon atoms in length is required for enzyme inhibitory activity. 7,11e,12 Thus, we needed to design a probe that retained these structural features of moenomycin and contained a site that could be easily derivatized for installation of a fluorophore. The crystal structures indicated that a fluorescent label attached to the C-ring N -acetyl group could be accommodated, since it points out of the enzyme binding pocket.…”