Functional Analysis of Degradative Enzymes for Hydroxyproline-linked ^|^beta;-L-Arabinofuranosides in Bifidobacterium longum

Abstract

Abstractβ-L-Arabinofuranosides are hydroxyproline (Hyp)-linked sugar chains of extensin observed in plant cell wall fractions. Despite the broad distribution of β-Larabinofuranosyl residues in plants, degradative enzymes have not yet been identified. In 2011, we cloned and characterized the first degradative enzymes for Hyp-linked β-L-arabinofuranosides from Bifidobacterium longum. These enzymes were composed of a glycoside hydrolase (GH) family 43 α-L-arabinofuranosidase (HypAA) releasing L-arabinose from Arafα1-3Arafβ1-2Arafβ1-2Arafβ-Hyp, a GH121 β-L-arabinobiosidase (HypBA2) releasing Arafβ1-2Araf (β-Ara 2 ) from Arafβ1-2Arafβ1-2Arafβ-Hyp, and a GH127 β-L-arabinofuranosidase (HypBA1) degrading β-Ara 2 to L-arabinose. These enzymes are encoded in a conserved gene cluster on several B. longum genomes, but not in genome sequences of other intestinal bacteria. Hyp-linked β-L-arabinofuranosides were utilized as carbohydrate sources by B. longum. This review presents the functional features of enzymes for Hyp-linked β-L-arabinofuranosides and the predicted metabolic pathway in B. longum. A. IntroductionL-Arabinose residues are the main constituents of sugars in plant cell walls, and they are mostly present in the form of α-L-furanose in polysaccharides such as arabinan, arabinoxylan, and pectic arabinogalactan. Glycoside hydrolases involved in the degradation of α-Larabinofuranosides are present in 6 glycoside hydrolase (GH) families (GH3, GH43, GH51, GH54, GH62, and GH93) in the CAZy database. In addition, degradative enzymes for α-and β-L-arabinopyranoside linkages were also found in the GH42 and GH27 families, respectively (1,2). On the other hand, β-L-arabinofuranoside linkages constitute sugar chains of hydroxyproline-rich glycoproteins (HRGPs), which are known

Mechanism of Cooperative Degradation of Gum Arabic Arabinogalactan Protein by Bifidobacterium longum Surface Enzymes

“…longum JCM1217 encodes nine α- l -arabinofuranosidase candidates, of which six are cell surface-anchoring GH43s and three are intracellular GH51s. In GH43s, HypAA (BLLJ_0213) contained the GH43 subfamily 29 (GH43_29) domain and was reported to be an α1,3-Ara f -specific α- l -arabinofuranosidase for degrading α- l -Ara f -(1→3)-β -l -Ara f -(1→2)-β- l -Ara f -(1→2)-β -l -Ara f -Hyp ( 10 ). BLLJ_1850 to BLLJ_1854 are arranged in tandem in the gene cluster, and we previously reported that BlArafA (BLLJ_1854) contained the GH43 subfamily 22 (GH43_22) domain acting on the α1,3-Ara f residue of larch AGP ( 11 ).…”

Two Novel α- l -Arabinofuranosidases from Bifidobacterium longum subsp. longum Belonging to Glycoside Hydrolase Family 43 Cooperatively Degrade Arabinan

“…Four GH43 enzymes, including BlArafC (GH43_27) and BlArafB (GH43_22), have been characterized. BLLJ_0213 encodes HypAA ␣-L-arabinofuranosidase (GH43_29), which specifically degrades ␣1,3-linked Araf in Araf␣1,3Araf␤1-2Araf␤1-2Araf␤1-hydroxyproline of plant glycoproteins (24). BLLJ_1840 encodes an exo-␤1,3-galactanase (GH43_24) that acts on the backbone of type II arabinogalactan (35).…”

“…We also reported that B. longum subsp. longum possesses a unique metabolic pathway to assimilate glycans from plant cell wall glycoproteins called extensins (23)(24)(25). Previous research suggests that oligosaccharides derived from plant matrix polysaccharides, such as arabinan, arabinoxylan, and arabinogalactan, are potential carbohydrate sources for adult-type bifidobacteria (26,27).…”

Bifidobacterial GH146 β‐l‐Arabinofuranosidase (Bll4HypBA1) as the Last Enzyme for the Complete Removal of Oligoarabinofuranosides from Hydroxyproline‐Rich Glycoproteins

“…[5,7,8] Additionally, X. euvesicatoria is also armed with a set of the l-Arafases [6] to degrade O-glycans, which are thought to facilitate their infection of target plants, such as tomato and pepper. [10] Among the l-Arafases, bifidobacterial α-l-Arafase (HypAA) [5] and Xanthomonas XeHypAA [6] (GH43) selectively hydrolyzes the terminal α-l-Araf-(1!3)-β-l-Araf structure in arabinooligosaccharides to expose the Hyp(l-Araf 3 ) and are susceptible to the subsequent action of GH121 β-l-Arafase (HypBA2) [7] and XeHypBA2 [6] to afford β-l-arabinobiose (β-Ara 2 ) and the monoβ-l-arabinofuranoside linked to the HRGP backbone (Figure 1). In bifidobacteria, the resultant β-l-arabinobiose is then hydrolyzed by GH127 β-l-Arafase (HypBA1; [8] Figure 1).…”

“…The arabinooligosaccharide components have been considered to endow plants with immunological protection against pathogens such as Xanthomonas euvesicatoria [9] . As the arabinooligosaccharide structures in the vegetables are not digested by human enzymes, intestinal bacteria such as Bifidobacterium longum assimilate their energy source using l ‐Ara f ases [5,7,8] . Additionally, X. euvesicatoria is also armed with a set of the l ‐Ara f ases [6] to degrade O ‐glycans, which are thought to facilitate their infection of target plants, such as tomato and pepper [10] .…”