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Abstract Background Expansins and expansin-like proteins loosen cellulose microfibrils, possibly through the rupture of intramolecular hydrogen bonds. Together with the use of lignocellulolytic enzymes, these proteins are potential molecular tools to treat plant biomass to improve saccharification yields. Results Here we describe a new type of expansin-related fungal protein that we have called loosenin. Its corresponding gene, loos1, from the basidiomycete Bjerkandera adusta, was cloned and heterologously expressed in Saccharomyces cerevisiae. LOOS1 is distantly related to plant expansins through the shared presence of a DPBB domain, however domain II found in plant expansins is absent. LOOS1 binds tightly to cellulose and chitin, and we demonstrate that cotton fibers become susceptible to the action of a commercial cellulase following treatment with LOOS1. Natural fibers of Agave tequilana also become susceptible to hydrolysis by cellulases after loosenin treatment. Conclusions LOOS1 is a new type of protein with disrupting activity on cellulose. LOOS1 binds polysaccharides, and given its enhancing properties on the action of hydrolytic enzymes, LOOS1 represents a potential additive in the production of fermentable sugars from lignocellulose.

Lignocellulose constitutes a raw material with considerable potential for the production of fermentable sugars and the generation of biofuels. In nature, lignocellulosic waste from forestry, agriculture and gardening acts as the preferred carbon source of a number of bacteria and fungi endowed with the required ligninolytic machinery. These hydrolytic activities could potentially be complemented with those from other proteins that remodel the structure of cell walls, such as expansins, a group of proteins originally identified in plants that have the capacity of relaxing cell wall tension to allow cell growth. Expansins participate in processes where remodeling of the plant cell wall is required: organogenesis, fruit ripening, and growth of the pollen tube, among others. Expansins and expansin-like proteins have been proposed to act by disrupting the hydrogen bonds binding together cellulose fibrils and cellulose and other polysaccharides through a non-enzymatic process, enhancing subsequent degradation. In this manuscript, a review on plant cell wall composition and ligninolytic enzymes from cell wall-degrading bacteria and fungi is presented. Proteins with expansin-like activity, their properties and their potential application to enhance sugar release from lignocellulosic material are also reviewed. [ABSTRACT FROM AUTHOR]

Lignocellulose constitutes a raw material with considerable potential for the production of fermentable sugars and the generation of biofuels. In nature, lignocellulosic waste from forestry, agriculture and gardening acts as the preferred carbon source of a number of bacteria and fungi endowed with the required ligninolytic machinery. These hydrolytic activities could potentially be complemented with those from other proteins that remodel the structure of cell walls, such as expansins, a group of proteins originally identified in plants that have the capacity of relaxing cell wall tension to allow cell growth. Expansins participate in processes where remodeling of the plant cell wall is required: organogenesis, fruit ripening, and growth of the pollen tube, among others. Expansins and expansin-like proteins have been proposed to act by disrupting the hydrogen bonds binding together cellulose fibrils and cellulose and other polysaccharides through a non-enzymatic process, enhancing subsequent degradation. In this manuscript, a review on plant cell wall compo-sition and ligninolytic enzymes from cell wall-degrading bacteria and fungi is presented. Proteins with expansin-like activity, their properties and their potential application to enhance sugar release from lignocellulosic material are also reviewed. [ABSTRACT FROM AUTHOR]

Cellulolytic properties of two white rot fungi, Bjerkandera adusta and Pycnoporus sanguineus, cultivated on wheat straw agar medium, were characterized and compared. Optimal growing parameters for maximum enzyme production for both fungi were wheat straw medium pH 5 and 28°C. B. adusta showed, on the 6th day of culture, carboxymethylcellulose (CMC)ase activity levels 1.6 times higher than maximal P. sanguineus activity, achieved on the 8th day. B. adusta supernatants also displayed higher activity levels towards xylan (3.6-fold) compared to those of P. sanguineus. However, enzymes from P. sanguineus were more robust resisting one hour incubation at high temperatures (up to 80°C), and exhibiting activity and stability in pH range from 2 to 8. Cellulolytic activities, with molecular masses ranging from 25 to 90 kDa, from the two species were detected in zymograms. [ABSTRACT FROM AUTHOR]