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Lysozyme activity of the Ruminococcus champanellensis cellulosome

Moraïs, Sarah, Cockburn, Darrell W., Ben‐David, Yonit, Koropatkin, Nicole M., Martens, Eric C., Duncan, Sylvia H., Flint, Harry J., Mizrahi, Itzhak, Bayer, Edward A.
Environmental microbiology 2016 v.18 no.12 pp. 5112-5122
Ruminococcus, adhesion, bacteria, cellobiose, cellulosome, digestive system, glycosides, humans, keystone species, lignocellulose, lysozyme, pH, temperature
Ruminococcus champanellensis is a keystone species in the human gut that produces an intricate cellulosome system of various architectures. A variety of cellulosomal enzymes have been identified, which exhibit a range of hydrolytic activities on lignocellulosic substrates. We describe herein a unique R. champanellensis scaffoldin, ScaK, which is expressed during growth on cellobiose and comprises a cohesin module and a family 25 glycoside hydrolase (GH25). The GH25 is non‐autolytic and exhibits lysozyme‐mediated lytic activity against several bacterial species. Despite the narrow acidic pH curve, the enzyme is active along a temperature range from 2 to 85°C and is stable at very high temperatures for extended incubation periods. The ScaK cohesin was shown to bind selectively to the dockerin of a monovalent scaffoldin (ScaG), thus enabling formation of a cell‐free cellulosome, whereby ScaG interacts with a divalent scaffodin (ScaA) that bears the enzymes either directly or through additional monovalent scaffoldins (ScaC and ScaD). The ScaK cohesin also interacts with the dockerin of a protein comprising multiple Fn3 domains that can potentially promote adhesion to carbohydrates and the bacterial cell surface. A cell‐free cellulosomal GH25 lysozyme may provide a bacterial strategy to both hydrolyze lignocellulose and repel eventual food competitors and/or cheaters.