Fungal-type carbohydrate binding modules from the coccolithophore Emiliania huxleyi show binding affinity to cellulose and chitin

Abstract

Six fungal-type cellulose binding domains were found in the genome of the coccolithophore Emiliania huxleyi and cloned and expressed in Escherichia coli. Sequence comparison indicate high similarity to fungal cellulose binding domains, raising the question of why these domains exist in coccolithophores. The proteins were tested for binding with cellulose and chitin as ligands, which resulted in the identification of two functional carbohydrate binding modules: EHUX2 and EHUX4. Compared to benchmark fungal cellulose binding domain Cel7A-CBM1 from Trichoderma reesei, these proteins showed slightly lower binding to birch and bacterial cellulose, but were more efficient chitin binders. Finally, a set of cellulose binding domains was created based on the shuffling of one well-functioning and one non-functional domain. These were characterized in order to get more information of the binding domain’s sequence–function relationship, indicating characteristic differences between the molecular basis of cellulose versus chitin recognition. As previous reports have showed the presence of cellulose in coccoliths and here we find functional cellulose binding modules, a possible connection is discussed.

Binding Forces of Cellulose Binding Modules on Cellulosic Nanomaterials

“…The carbohydrate-binding activity of CBMs on cellulose fibers from different origins has been widely studied in recent years − with a focus on understanding the enzymatic hydrolysis of the renewable lignocellulosic biomass and for the development of hydrolase kinetic models . Degradation of cellulose by microbial enzymes has also been considered an important biological and industrial process to produce environmentally friendly biofuels .…”

“…Among the CBMs, the Cel7A-CBM1 is an attractive choice as an anchoring unit for functional surfaces due to its high binding affinity on cellulose . The three aromatic residues of the down face of Cel7A-CBM1 represent the driving interaction for binding to cellulose (Figure ).…”

“…14 Among the CBMs, the Cel7A-CBM1 is an attractive choice as an anchoring unit for functional surfaces due to its high binding affinity on cellulose. 10 The three aromatic residues of the down face of Cel7A-CBM1 represent the driving interaction for binding to cellulose (Figure 1). The interaction between CBM1 and cellulose is a combination of stacking of aromatic residues due to π-electron interactions and hydrogen bonding, which together cause specificity between the CBM and a cellulosic crystal.…”

Kinetics of Calcite Nucleation onto Sulfated Chitosan Derivatives and Implications for Water–Polysaccharide Interactions during Crystallization of Sparingly Soluble Salts

“…In marine animals, sulfate-functionalized macromolecules are often present alongside chitin, an abundant, structural, amide-functionalized polysaccharide. − For example, the internal shell of the cuttlefish (i.e., cuttlebone) has two main components: a chambered body part and a dorsal shield. , Chitin fibers encase CaCO 3 in both parts of the cuttlebone, but other macromolecules (many sulfated) are found at specific sites and contain unique chitin-binding domains. These macromolecules are proposed to direct CaCO 3 formation into the pillars and lamellae that produce chambers or terraces that, in turn, form compact sublayers of the shield. − Similar associations are described in other organisms, including mollusks, , brachiopods, lobsters, barnacles, coralline algae, and coccolithophores. , …”

“…32−34 Similar associations are described in other organisms, including mollusks, 35,36 brachiopods, 35 lobsters, 37 barnacles, 24 coralline algae, 38 and coccolithophores. 39,40 Understanding how the composition of macromolecules leads to complex natural composites also holds promise for environmental, clean energy, and biomedical applications. 41−43 For example, tailored dispersions of CaCO 3 could enhance the capability of biopolymers to remove heavy metals and pollutants for water treatment and soil remediation.…”