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Fakultätsübergreifend / Sonstige Einrichtung

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    Charakterisierung der antimikrobiellen Aktivität von High-mobility group box 2
    (2013) Küchler, Robert; Wehkamp, Jan
    The human body is continuously exposed to an enormous amount of microbes. Especially surfaces like the skin or the gastrointestinal mucosa are in close contact with large numbers of microorganisms, including bacteria, fungi and viruses. A very effective innate immune system protects the intestinal mucosa from an overgrowth of commensal bacteria and penetration by pathogenic microbes. Besides an efficient layer of thick mucus, antimicrobial peptides and proteins (AMPs) which can inhibit the growth of microorganisms or even destroy them are an essential part of the epithelial barrier. In 2009, as a part of my diploma thesis, I could show that high-mobility group box 2 (HMGB2) exhibits antimicrobial activity against E. coli. The aim of this PhD thesis was to characterize and further clarify this new function. HMGB2 was recombinantly expressed and systematically analyzed for antimicrobial activity. Notably, several gram-negative and gram-positive bacteria of the normal gut flora were critically affected by HMGB2. In addition, bactericidal properties against the pathogenic bacterial strain Staphylococcus aureus were detected via electron microscopic analysis. Furthermore potential influences of intestinal environmental conditions on the activity of HMGB2 were investigated. Changes in the pH or the generation of a reducing environment altered the activity of the protein only to a small amount. To localize the part of HMGB2 which is essential for its antimicrobial activity, three peptides which represent three regions of the protein were recombinantly expressed. An activity screening with the three peptides showed that the two DNA-binding-domains HMG-Box A and B are crucial for the antimicrobial effects. An expression study showed that HMGB2 is present in all analyzed stomach and intestinal sections. In addition, the expression in patients with inflammatory bowel disease (IBD) was studied. No significant differences between patients with Crohn?s disease, ulcerative colitis and unaffected controls were detected. However, the examination of stool from individuals of these three groups suggests that HMGB2 might be useful as a new marker for intestinal inflammation. In summary, HMGB2 exhibits antimicrobial activity against various commensal bacteria of the normal gut flora and is expressed in all analyzed gastrointestinal tract sections. HMGB2 is part of the intestinal barrier and protects, together with other AMPs, the intestine from microorganisms.