@phdthesis{Reisky2019,
  author    = {Lukas Reisky},
  title     = {Discovery and Characterization of Novel Carbohydrate-Active Enzymes from Marine Bacteria},
  journal    = {Identifizierung und Charakterisierung von Neuen Kohlenhydrataktiven Enzymen aus Marinen Bakterien},
  url       = {https://nbn-resolving.org/urn:nbn:de:gbv:9-opus-27050},
  pages     = {233},
  year      = {2019},
  abstract  = {Half of the global primary production is realized in the ocean and a large proportion of the fixed CO2 is used to produce algal polysaccharides. These carbohydrates are a main carbon and energy source fueling marine food webs where they are degraded into monomeric sugars by carbohydrate active enzymes. As the knowledge about the enzymatic degradation of algal polysaccharides in the ocean is still scarce, this thesis aimed to contribute to a deeper understanding of these processes. O-methylation of sugars is a common and very stable modification in marine and terrestrial polysaccharides. It was shown in Article I that cytochrome P450 monooxygenases are an integral part of agar depolymerization systems from marine bacteria where these enzymes catalyze the oxidative demethylation of 6-O-methyl-D-galactose, a monomer found in red algal polysaccharides. These findings place the P450 subfamily CYP236A into the group of carbohydrate-active enzymes as a second class of monooxygenases. The characterized P450s are highly specific for 6 O methyl D galactose and do not accept typical P450 substrates. To understand the molecular determinants for the specific conversion of the polar substrate, protein crystallography was used (Article II). The crystal structure of the P450 from Z. galactanivorans bound to a substrate molecule showed that hydrogen bonding and hydrophobic interactions are involved in substrate recognition, which was further supported by ITC experiments and mutational studies. Fast growing green algae from the genus Ulva cause dangerous algal blooms worldwide. A main constituent of the formed biomass is the anionic polysaccharide ulvan. Enzymatic ulvan degradation was only poorly understood, hampering the use of Ulva biomass in a productive way. The detailed biochemical characterization of an ulvan lyase from F. agariphila is shown in Article III. This enzyme catalyzes the initial step in ulvan degradation and the biochemical parameters match the conditions found in coastal regions of the temperate ocean, the area from which the bacterium was isolated. The subsequent enzymatic steps for the complete degradation of ulvan were elucidated and described in Article IV for the first time. 13 enzymes belonging to the classes of polysaccharide lyases, glycoside hydrolases and sulfatases act together in a complex cascade to eventually produce monosaccharides from ulvan. The presented discovery and characterization of novel carbohydrate-active enzymes do not only contribute to a better understanding of the processes involved in the marine carbon cycle but are also of significant importance for future biotechnological processes. An efficient enzymatic depolymerization of algal polysaccharides will be necessary for biorefinery concepts that are based on algal carbohydrates as starting material for microbial fermentation to produce second generation biofuels and other useful products.},
  language  = {de}
}