Diversity of GH51 α-L-arabinofuranosidase homolog sequences from subantarctic intertidal sediments

Bacteria from coastal habitats exposed to challenging environmental conditions constitute a promising source of enzymes with novel catalytic properties for the depolymerization of complex carbohydrates of terrestrial and marine origins. In this work, we investigated the sequence and structural diversity of putative enzymes related to the glycoside hydrolase family 51 (GH51) identified in a metagenomic dataset of intertidal sediments from a subantarctic environment. The majority of the characterized members of the GH51 family are α- L -arabinofuranosidases (EC 3.2.1.55), enzymes with important industrial applications that catalyze the hydrolysis of side chains from arabinose-substituted polysaccharides. The 28 sequences identified in the metagenome were highly diverse and were assigned to the Bacteroidota, Planctomycetota, Chloroflexota, Pseudomonadota, and Kiritimatiellaeota phyla, with four sequences remaining unassigned. In a sequence similarity network, most GH51 homolog sequences clustered with uncharacterized members of the GH51 family or were highly divergent. Three-dimensional models of the putative enzymes showed distinctive structural characteristics, including a highly variable length of the loop located between β-strand 2 and α-helix 2 and the absence in some of the sequences of a highly conserved Trp residue in this loop. Important differences in the predicted surface electrostatic potential in models of closely related GH51 homologs suggest various levels of adaptation to the prevailing environmental conditions. This work provides an insight into the characteristics of putative enzymes related to the GH51 family from intertidal sediment bacteria, from taxa that are relevant in the marine environment but remain poorly characterized due to the difficulties in their cultivation.