Opportunities and Challenges of Bacterial Glycosylation for the Development of Novel Antibacterial Strategies

Abstract

Glycosylation is a ubiquitous process that is universally conserved in nature. The various products of glycosylation, such as polysaccharides, glycoproteins, and glycolipids, perform a myriad of intra- and extracellular functions. The multitude of roles performed by these molecules is reflected in the significant diversity of glycan structures and linkages found in eukaryotes and prokaryotes. Importantly, glycosylation is highly relevant for the virulence of many bacterial pathogens. Various surface-associated glycoconjugates have been identified in bacteria that promote infectious behavior and survival in the host through motility, adhesion, molecular mimicry, and immune system manipulation. Interestingly, bacterial glycosylation systems that produce these virulence factors frequently feature rare monosaccharides and unusual glycosylation mechanisms. Owing to their marked difference from human glycosylation, bacterial glycosylation systems constitute promising antibacterial targets. With the rise of antibiotic resistance and depletion of the antibiotic pipeline, novel drug targets are urgently needed. Bacteria-specific glycosylation systems are especially promising for antivirulence therapies that do not eliminate a bacterial population, but rather alleviate its pathogenesis. In this review, we describe a selection of unique glycosylation systems in bacterial pathogens and their role in bacterial homeostasis and infection, with a focus on virulence factors. In addition, recent advances to inhibit the enzymes involved in these glycosylation systems and target the bacterial glycan structures directly will be highlighted. Together, this review provides an overview of the current status and promise for the future of using bacterial glycosylation to develop novel antibacterial strategies.

Synthesis and Application of Rare Deoxy Amino l-Sugar Analogues to Probe Glycans in Pathogenic Bacteria

“…For example, Western blot data hinted at subtle processing of L-FucNAz (5) and L-PneNAz (6) into glycans in P. shigelloides, consistent with the presence of these epitopes in P. shigelloides serotype O1 (Figure 1C). 28 Moreover, subtle yet detectable incorporation of L-FucNAz (5), L-RhaNAz (7), and L-QuiNAz (8) into V. vulnificus surface glycans matched reports of these monosaccharides in V. vulnificus M06-24 and BO62316. 29,70 Further, the reported D-Ac 2 Bac-diNAz (4) probe was robustly incorporated into P. shigelloides, in line with reports of bacillosamine in this bacteria.…”

“…Metabolic incorporation of L-sugar analogues was subtle yet detectable relative to the negative control, with all L-azidosugar analogues leading to labeling of glycans in P. shigelloides and V. vulnificus (Figure 3A). Of note, L-FucNAz (5), L-PneNAz (6), L-RhaNAz (7), and L-QuiNAz (8) led to subtle labeling of glycans between 50 and 130 kDa in P. shigelloides and V. vulnificus (Figure 3A). In contrast, Western blot analysis did not reveal detectable incorporation of any established analogues or L-sugar probes in S. aureus (Figure 3A; Figure S1).…”

“…H. pylori used L-sugar analogues 5−8 as metabolic substrates and incorporated these analogues into discrete species (Figure 4A) that correspond to surface-accessible glycans (Figure 4B). Supple-mentation of C. jejuni with the panel of L-sugar analogues 5−8 led to no apparent detection of azide-labeled glycans by Western blot relative to azide-free controls (Figure 4; Figure S2), yet low but significant incorporation of L-RhaNAz (7) and L-QuiNAz (8) observed by flow cytometry (Figure 4; Figure S2). By contrast, supplementation of B. f ragilis with the panel of L-sugar analogues 5−8 led to no detection of azide-labeled glycans by Western blot relative to azide-free controls (Figure 4; Figure S2), despite high protein content in these samples (Figure S2).…”

“…4), and Phos-FLAG were synthesized as previously described. 44,57,85 L-FucNAz (5), L-PneNAz (6), L-RhaNAz (7), and L-QuiNAz (8) were synthesized using standard organic chemistry procedures and characterized by standard techniques including 1 H and 13 C NMR spectroscopy and mass spectrometry. Analogues 5−8 were purified using flash silica gel chromatography.…”

A Structural Approach to Anti-Virulence: A Discovery Pipeline

“…A compelling, innovative, and alternative approach to antibiotic therapy is the antivirulence or anti-infective strategy that involves targeting virulence-associated rather than survival/fitness-relevant traits in the offending pathogen [8][9][10][11][12][13]. Thus, the "anti-infective" agent/drug interferes with the pathogen's ability to cause disease [14,15]. One avenue for this approach is to target bacterial toxins using this powerful method [9,[16][17][18][19].…”