Arabinogalactan proteins (AGPs) are a family of plant cell surface proteoglycans and are considered to be involved in plant growth and development. Because AGPs are very complex molecules, glycoside hydrolases capable of degrading AGPs are powerful tools for analyses of the AGPs. We previously reported such enzymes from Streptomyces avermitilis. Recently, a ␤-Larabinopyranosidase was purified from the culture supernatant of the bacterium, and its corresponding gene was identified. The primary structure of the protein revealed that the catalytic module was highly similar to that of glycoside hydrolase family 27 (GH27) ␣-D-galactosidases. The recombinant protein was successfully expressed as a secreted 64-kDa protein using a Streptomyces expression system. The specific activity toward p-nitrophenyl-␤-L-arabinopyranoside was 18 mol of arabinose/min/mg, which was 67 times higher than that toward pnitrophenyl-␣-D-galactopyranoside. The enzyme could remove 0.1 and 45% L-arabinose from gum arabic or larch arabinogalactan, respectively. X-ray crystallographic analysis reveals that the protein had a GH27 catalytic domain, an antiparallel ␤-domain containing Greek key motifs, another antiparallel ␤-domain forming a jellyroll structure, and a carbohydrate-binding module family 13 domain. Comparison of the structure of this protein with that of ␣-D-galactosidase showed a single amino acid substitution (aspartic acid to glutamic acid) in the catalytic pocket of ␤-L-arabinopyranosidase, and a space for the hydroxymethyl group on the C-5 carbon of D-galactose bound to ␣-galactosidase was changed in ␤-L-arabinopyranosidase. Mutagenesis study revealed that the residue is critical for modulating the enzyme activity. This is the first report in which ␤-L-arabinopyranosidase is classified as a new member of the GH27 family.Arabinogalactan proteins (AGPs) 3 are a family of complex proteoglycans widely distributed in plants (1, 2). AGPs are also found in tree exudate gums and coniferous woods (3) and are characterized by the presence of large amounts of carbohydrate components rich in galactose (all the sugars in the present study are in the D-configuration unless otherwise specified) and L-arabinose and by protein components rich in hydroxyproline, serine, threonine, alanine, and glycine (4). Type II arabinogalactans and short oligosaccharides are the two types of carbohydrates attached to the AGP backbone. Type II arabinogalactans have ␤-1,3-linked galactosyl backbones in mono-or oligo-␤-1,6-galactosyl and/or L-arabinosyl side chains (2, 5). L-Arabinose and lesser amounts of other auxiliary sugars such as glucuronic acid, L-rhamnose, and L-fucose are attached to the side chains primarily at nonreducing termini (2). Molecular and biochemical evidence indicates that AGPs have specific functions during root formation, promotion of somatic embryogenesis, and attraction of pollen tubes to the style (6). However, because many putative protein cores exist and the structures of the carbohydrate moieties are complex, it has been difficult...

Background: Glycoside hydrolase family 62 ␣-L-arabinofuranosidases specifically release L-arabinose from arabinoxylan. Results: The crystal structure of glycoside hydrolase family 62 ␣-L-arabinofuranosidase from Streptomyces coelicolor was determined. Conclusion: L-Arabinose and xylohexaose complexed structures revealed the mechanism of substrate specificity of this enzyme. Significance: Efficient catalysis by glycoside hydrolase family 62 ␣-L-arabinofuranosidase requires its binding to terminal xylose sugars at the substrate-binding cleft.

e We cloned two glycoside hydrolase family 74 genes, the sav_1856 gene and the sav_2574 gene, from Streptomyces avermitilis NBRC14893 and characterized the resultant recombinant proteins. The sav_1856 gene product (SaGH74A) consisted of a catalytic domain and a family 2 carbohydrate-binding module at the C terminus, while the sav_2574 gene product (SaGH74B) consisted of only a catalytic domain. SaGH74A and SaGH74B were expressed successfully and had molecular masses of 92 and 78 kDa, respectively. Both recombinant proteins were xyloglucanases. SaGH74A had optimal activity at 60°C and pH 5.5, while SaGH74B had optimal activity at 55°C and pH 6.0. SaGH74A was stable over a broad pH range (pH 4.5 to 9.0), whereas SaGH74B was stable over a relatively narrow pH range (pH 6.0 to 6.5). Analysis of the hydrolysis products of tamarind xyloglucan and xyloglucan-derived oligosaccharides indicated that SaGH74A was endo-processive, while SaGH74B was a typical endo-enzyme. The C terminus of SaGH74A, which was annotated as a carbohydrate-binding module, bound to ␤-1,4-linked glucan-containing soluble polysaccharides such as hydroxyethyl cellulose, barley glucan, and xyloglucan.

Ferulic acid (FA), which is present in the cell walls of some plants, is best known for its antioxidant property. By combining a commercial enzyme that shows FA esterase activity with several Streptomyces carbohydrate-hydrolyzing enzymes, we succeeded in enhancing the enzymatic production of FA from defatted rice bran. In particular, the combination of three xylanases, an α-L-arabinofuranosidase, and an acetyl xylan esterase from Streptomyces spp. produced the highest increase in the amount of released FAs among all the enzymes in the Streptomyces enzymes library. This enzyme combination also had an effect on FA production from other biomasses, such as raw rice bran, wheat bran, and corncob.

Ferulic acid (FA), a component of hemicellulose in plant cell walls, is a phenolic acid with several potential applications based on its antioxidant properties. Recent studies have shown that feruloyl esterase (FAE) is a key bacterial enzyme involved in FA production from agricultural biomass. In this study, we screened a library of 43 esterases from Streptomyces species and identified two enzymes, R18 and R43, that have FAE activity toward ethyl ferulate. In addition, we characterized their enzyme properties in detail. R18 and R43 showed esterase activity toward other hydroxycinnamic acid esters as well, such as methyl p-coumarate, methyl caffeate, and methyl sinapinate. The amino acid sequences of R18 and R43 were neither similar to each other, nor to other FAEs. We found that R18 and R43 individually showed the ability to produce FA from corn bran; however, combination with other Streptomyces enzymes, namely xylanase and α-l-arabinofuranosidase, increased FA production from biomass such as corn bran, defatted rice bran, and wheat bran. These results suggest that R18 and R43 are effective FAEs for the enzymatic production of FA from biomass.