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Sasaki et al. Microbiome Res Rep 2023;2:12 https://dx.doi.org/10.20517/mrr.2023.08 Page 13 of 15

[31]
main chain degrading enzyme (Bl1,3Gal) , side chain degrading enzyme (Bl1,6Gal), and α-L-
[7]
arabinofuranosidase (BlArafA) , which had been characterized in B. longum JCM1217. Therefore, this
strain probably has other uncharacterized enzymes that degrade β-1,3/1,6-galactan and/or α-L-
arabinofuranoside chains on larch AGP.

GH39 GAfase homologs are widely conserved across Bifidobacterium strains and are novel candidates for
AGP-degrading enzymes. The GH39 homolog from B. catenulatum JCM1194, which has 28% amino acid
sequence identity with GAfase, is adjacent to the GH127 putative β-L-arabinofuranosidase gene.
Considering that the neighboring gene tends to be associated with a series of reactions, it may degrade and
release an oligosaccharide containing β-L-Araf structures. The side chain structure of AGP varies depending
on plant species, e.g., the side chain structure of gum arabic AGP from Acacia seyal differs from that of gum
arabic AGP from Acacia senegal, in which it is substituted by L-Araf oligomers instead of α-D-Gal-(1→3)-α-
L-Araf-(1→3) . Further investigations are warranted to elucidate the functional diversity of
[32]
Bifidobacterium GH39s corresponding to the structural diversity of AGPs.

DECLARATIONS
Acknowledgments
We thank Prof. Takane Katayama and Dr. Akihiro Ishiwata for the useful discussion and suggestions. We
also thank Dr. Toma Kashima for the technical support for the structural analysis using AlphaFold2.

Authors’ contributions
Conceived and designed the experiments: Fujita K, Kitahara K, Odamaki T, Xiao JZ
Performed data acquisition and analysis: Sasaki Y, Yanagita M, Hashiguchi M, Horigome A
Drafted the manuscript: Sasaki Y
Edited the manuscript and supervised the study: Fujita K
Discussed the data and contributed to completing the final manuscript: Sasaki Y, Yanagita M, Hashiguchi
M, Horigome A, Xiao JZ, Odamaki T, Kitahara K, Fujita K

Availability of data and materials
The sequence of the synthesized MCC10289_0425 gene has been deposited in the DDBJ databank under the
accession number LC745705.

Financial support and sponsorship
This work was supported in part by JSPS KAKENHI Grant-in-Aid, Grant Numbers 19J20806 (to Sasaki Y);
And 19K05816 (to Fujita K).

Conflicts of interest
Horigome A, Xiao JZ, and Odamaki T are employees of Morinaga Milk Industry Co., Ltd. The authors
declared that there are no other conflicts of interest.

Ethical approval and consent to participate
Not applicable.

Consent for publication
Not applicable.