Structure-function-activity relationships of enzymatic systems for bioconversion and biodegradation



Structure-function-activity relationships of enzymatic systems for bioconversion and biodegradation


A. Cassetta, D.Lamba, A. Pesaresi


Bacillus pumilus, Enzymatic hydrolysis; Acetyl xylan esterase; Arabinofuranosidase; Bioethanol


International Centre for Genetic Engineering and Biotechnology, Trieste (Italy); Sincrotrone Trieste S.C.p.A., Trieste (Italy)


As a clean and readily available agricultural residue, corn bran may have the potential of becoming a source for new C5 biofuel products or for the manufacture of food ingredients. These novel uses require partial or complete degradation of the biomass to its constituent monomers. Corn bran originates from a gramineaceous plant having a primary cell wall that is mainly composed of heteroxylans, notably arabinoxylan.
The arabinoxylan backbone in corn bran is composed of a xylan backbone of β-(1-->4)-linked D-xylopyranosyl residues. Linkage analysis has suggested that up to 85% of the xylopyranosyl moieties are substituted with various components. The xylose units in the backbone are decorated with different kind of side chain substitutions.
Most common substituents are represented by arabinose, 4-O-methylglucuronic acid and acetyl moieties.
To achieve the complete degradation of such a complex molecule a set of enzymes is required. The hydrolysis of β (1-->4) -D-xylan is accomplished by endo-xylanases which break the β ( 1-->4) glycosidic bonds between xylopyranosyl moieties. The products of the hydrolysis are short xylo-oligosaccharides, usually of a size between two and six sugar units. An additional endo-(1-->3) xylosidase and β-xylosidases carry out the complete degradation of the chain to simple sugar moieties. The substituents side chain groups are hydrolyzed α-L-arabinofuranosidases, α-glucuronidases and acetyl xylan esterases.


Structure-function-activity relationships of enzymatic systems for bioconversion and biodegradation - Img


The present study is aimed at revealing the structure-function-activity relationships of the acetyl xylan esterase and α-L-arabinofuranosidase from Bacillus pumilus in a combined effort to identify and understand their catalytic mechanism, substrate specificity and metabolic function.

Krastanova I., Guarnaccia C., Zahariev S., Degrassi G., Lamba D. Heterologous expression, purification, crystallization, X-ray analysis and phasing of the acetyl xylan esterase from Bacillus pumilus. Biochimica et Biophysica Acta - Proteins and Proteomics (2005) 1748, 222.

Krastanova I, Cassetta A, Biely P, Lamba, D. Structural and functional studies of Bacillus pumilus acetyl xylan esterase: Insights into the deacetylation activity of a hexameric enzymatic assembly. Biochemical J (2010), in preparation.


Doriano Lamba
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Last Updated (Tuesday, 21 December 2010 16:01)