Human tandem-repeat-type galectins bind bacterial non-βGal polysaccharides

Abstract

Galectins are multifunctional effectors, for example acting as regulators of cell growth via protein-glycan interactions. The observation of capacity to kill bacteria for two tandem-repeat-type galectins, which target histo-blood epitopes toward this end (Stowell et al. Nat. Med. 16:295-301, 2010), prompted us to establish an array with bacterial polysaccharides. We addressed the question whether sugar determinants other than β-galactosides may be docking sites, using human galectins-4, -8, and -9. Positive controls with histo-blood group ABH-epitopes and the E. coli 086 polysaccharide ascertained the suitability of the set-up. Significant signal generation, depending on type of galectin and polysacchride, was obtained. Presence of cognate β-galactoside-related epitopes within a polysaccharide chain or its branch will not automatically establish binding properties, and structural constellations lacking galactosides, like rhamnan, were found to be active. These data establish the array as valuable screening tool, giving direction to further functional and structural studies.

Microbial glycan microarrays define key features of host-microbial interactions

“…Recent studies demonstrate that synthetic microbial glycans or glycans directly harvested from microbes coupled in an array format can be used to characterize serological specificity for distinct microbes 13–23 , demonstrating that glycans can be readily harvested from a variety of microbes and examined in parallel to evaluate host-microbial interactions. As host immune factors work in concert to interact with a variety of microbial determinants, yet the individual structural motifs required for the binding of many host immune factors remain unknown, we isolated a diverse set of previously defined microbial glycans from a broad range of microbial genera to provide a platform for defining host factor interactions with specific microbial glycans.…”

Specificity of human galectins on cell surfaces

“…It should not be excluded that high affinity ligands of galectins are not glycans, per se, but molecular patterns (microbe associated (MAMP) or damage associated molecular patterns (DAMP) [46,47]), which contain glycans. This version is supported by several papers describing nonclassical interactions of galectins, in par ticular, (1) human tandem repeat galectins bind to bac terial E. coli O86 polysaccharide related to blood group B antigenic determinant [48,49], (2) tandem repeat type galectins bind to rhamnopolysaccharide of E. coli 19ab, which contains no "classical" galectin binding motifs like Galβ1 4GlcNAc [49]; (3) gal 3 interacts with β1,2 mannosides from Candida albicans [50]; (4) gal 3, 7, and 9 bind to partially desulfated glycosaminoglycans [51].…”

Glycan Arrays: From Basic Biochemical Research to Bioanalytical and Biomedical Applications

“…The specificities of many human galectins toward many glycans have been firmly established by glycan array analyses (17,18,88,89). Ligands beyond β-galactosides, such as α(1→2) rhamnans, have been discovered (90). On a microarray of 48 isolated bacterial polysaccharides, human galectin-3, -4, and -8 specifically recognized the Providencia alcalifaciens O5 lipopolysaccharide (LPS) O-antigen presenting the terminal disaccharide of the α-Gal epitope (13).…”