Gram-positive bacteria are held at a distance in the colon mucus by the lectin-like protein ZG16

Abstract

The distal colon functions as a bioreactor and harbors an enormous amount of bacteria in a mutualistic relationship with the host. The microbiota have to be kept at a safe distance to prevent inflammation, something that is achieved by a dense inner mucus layer that lines the epithelial cells. The large polymeric nets made up by the heavily O-glycosylated MUC2 mucin forms this physical barrier. Proteomic analyses of mucus have identified the lectin-like protein ZG16 (zymogen granulae protein 16) as an abundant mucus component. To elucidate the function of ZG16, we generated recombinant ZG16 and studied Zg16 −/− mice. ZG16 bound to and aggregated Gram-positive bacteria via binding to the bacterial cell wall peptidoglycan. Zg16−/− mice have a distal colon mucus layer with normal thickness, but with bacteria closer to the epithelium. Using distal colon explants mounted in a horizontal perfusion chamber we demonstrated that treatment of bacteria with recombinant ZG16 hindered bacterial penetration into the mucus. The inner colon mucus of Zg16 −/− animals had a higher load of Gram-positive bacteria and showed bacteria with higher motility in the mucus close to the host epithelium compared with cohoused littermate Zg16. The more penetrable Zg16−/− mucus allowed Gram-positive bacteria to translocate to systemic tissues. Viable bacteria were found in spleen and were associated with increased abdominal fat pad mass in Zg16animals. The function of ZG16 reveals a mechanism for keeping bacteria further away from the host colon epithelium.mucin | colon | inflammation | obesity | peptidoglycan

Eukaryotic protein glycosylation: a primer for histochemists and cell biologists

“…Representative techniques are listed as follows:

Detection of glycans as carbohydrates in glycoproteins using chemical assays. This can be applied for screening in standard fractionation techniques such as high-performance liquid chromatography, size fractionation chromatography, ion-exchange chromatography, electrophoretic methods and density gradient centrifugation (Brockhausen et al 1988; Nakagawa 2009; Marino et al 2010).

Detection of glycans as carbohydrates in tissue sections using chemical assays to provide morphological data regarding the localization of the carbohydrate/glycoprotein (Filipe and Branfoot 1983; Buk and Filipe 1986; Warren 1993; Filipe and Ramachandra 1995; Corfield and Warren 1996) (for an example on the identification of O -acetylated sialic acids in human colon using the mild-PAS method, please see Fig.

…”

“…This can be applied for screening in standard fractionation techniques such as high-performance liquid chromatography, size fractionation chromatography, ion-exchange chromatography, electrophoretic methods and density gradient centrifugation (Brockhausen et al 1988; Nakagawa 2009; Marino et al 2010). …”

“…The secreted mucins are an example, where viscoelasticity and gel formation establish a protective barrier on mucosal surfaces (Newton et al 2000; Pearson et al 2000; Atuma et al 2001; Allen and Flemström 2005; Gustafsson et al 2012; Johansson and Hansson 2012; Verdugo 2012; Berry et al 2013; Birchenough et al 2015). …”

“…O -Mannose α-linked to serine and threonine residues is commonly found in the metazoans, largely in skeletal muscle and the brain and nervous system (Lommel and Strahl 2009; Vester-Christensen et al 2013; Panin and Wells 2014; Neubert and Strahl 2016). A tetrasaccharide, Neu5Acα2,3Galβ1,4Glc N Acβ1,2ManαSer/Thr is found in the skeletal muscle protein α-dystroglycan, and most O -mannose glycans are related to this structure despite additional modifications with fucose, glucuronic acid and sulphate (Panin and Wells 2014). …”

“…In view of the increasing awareness that their structure is an ideal platform to store information [Winterburn and Phelps 1972; Gabius 2009, 2015; please see also the introduction to this theme issue (Gabius and Roth 2017)], a survey of their characteristics is timely. In connection with the overview on glycolipids (Kopitz 2017, this issue), an introduction to protein glycosylation is provided here.…”