page_title: Dispersin B
section_title: Enzyme Structure
hierarchical_section_title: Dispersin B / Enzyme Structure
caption_attribution_description: English: Made in Microsoft Word
context_page_description: Dispersin B is a 40 kDa glycoside hydrolase produced by the periodontal pathogen, Aggregatibacter actinomycetemcomitans. The bacteria secrete Dispersin B to release adherent cells from a mature biofilm colony by disrupting biofilm formation. The enzyme catalyzes the hydrolysis of linear polymers of N-acetyl-D-glucosamines found in the biofilm matrices. Poly-acetyl glucosamines are integral to the structural integrity of the biofilms of various Gram-positive bacteria and Gram-negative bacteria and are referred to as PIA in Staphylococcus species and PGA in Escherichia coli. By degrading the biofilm matrix, Dispersin B allows for the release of bacterial cells that can adhere to new surfaces close by and extend the biofilm or start new colonies. Currently there is interest in Dispersin B as a commercial anti-biofilm agent that could be combined with antibiotics for the treatment of bacterial infections.
context_section_description: The three-dimensional structure of dispersin B was determined by expressing the protein in E. coli, purifying it from cultures, and crystallizing it in the orthoorhombic space group C2221 with one molecule in the asymmetric unit.  It is a 361 amino acid protein consisting of a single domain. The major substructure consists of residues 1-60 and residues 91-358, which fold into a β/α structure of a typical TIM barrel. The loop β4 contains two highly conserved residues Asp183 and Glu184 that are part of the enzyme's active site, a large cavity in the center of the bowl-shaped Dispersin B molecule. 
  The oligomer substrate binding and cleaving at the active site of Dispersin B was studied to learn more about the enzymatic degradation. Reverse phase HPLC was used to analyze the products of the hydrolysis of substrates with differing degrees of polymerization. Chain lengthening of the substrate was shown to increase the catalytic efficiency of Dispersin B. A substrate with a degree of polymerization of five was not enough for total subsite occupancy. Carbamate substrates were also shown to improve the activity of the enzyme relative to the benchmark substrate 4-nitrophenyl N-acetyl-β-D-glucosamine.
caption: Single Domain of Dispersin B: TIM Barrel (major substructure) shown in blue. α-Helices are represented by cylinders and β-strands represented by arrows
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