*Article* **Architecture Insight of Bifidobacterial** α**-L-Fucosidases**

**José Antonio Curiel \* , Ángela Peirotén , José María Landete , Ana Ruiz de la Bastida, Susana Langa and Juan Luis Arqués**

> Departamento de Tecnología de Alimentos, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA-CSIC), Carretera de La Coruña Km 7.5, 28040 Madrid, Spain; angela.peiroten@inia.es (Á.P.); landete.josem@inia.es (J.M.L.); ana.ruiz@inia.es (A.R.d.l.B.); langa.susana@inia.es (S.L.); arques@inia.es (J.L.A.) **\*** Correspondence: joseantonio.curiel@inia.es; Tel.: +34-91-347-68-86

**Abstract:** Fucosylated carbohydrates and glycoproteins from human breast milk are essential for the development of the gut microbiota in early life because they are selectively metabolized by bifidobacteria. In this regard, α-L-fucosidases play a key role in this successful bifidobacterial colonization allowing the utilization of these substrates. Although a considerable number of α-L-fucosidases from bifidobacteria have been identified by computational analysis, only a few of them have been characterized. Hitherto, α-L-fucosidases are classified into three families: GH29, GH95, and GH151, based on their catalytic structure. However, bifidobacterial α-L-fucosidases belonging to a particular family show significant differences in their sequence. Because this fact could underlie distinct phylogenetic evolution, here extensive similarity searches and comparative analyses of the bifidobacterial α-L-fucosidases identified were carried out with the assistance of previous physicochemical studies available. This work reveals four and two paralogue bifidobacterial fucosidase groups within GH29 and GH95 families, respectively. Moreover, *Bifidobacterium longum* subsp. *infantis* species exhibited the greatest number of phylogenetic lineages in their fucosidases clustered in every family: GH29, GH95, and GH151. Since α-L-fucosidases phylogenetically descended from other glycosyl hydrolase families, we hypothesized that they could exhibit additional glycosidase activities other than fucosidase, raising the possibility of their application to transfucosylate substrates other than lactose in order to synthesis novel prebiotics.

**Keywords:** bifidobacteria; fucosidases; glycosyl hydrolases; conserved domains; human milk
