Beschreibung:
<jats:p>Marine bacteria catabolize carbohydrate polymers of algae, which synthesize these structurally diverse molecules in ocean surface waters. Although algal glycans are an abundant carbon and energy source in the ocean, the molecular details that enable specific recognition between algal glycans and bacterial degraders remain largely unknown. Here we characterized a surface protein, <jats:styled-content style="fixed-case">GMS</jats:styled-content>usD from the planktonic Bacteroidetes‐Gramella sp. <jats:styled-content style="fixed-case">MAR</jats:styled-content>_2010_102 that thrives during algal blooms. Our biochemical and structural analyses show that <jats:styled-content style="fixed-case">GMS</jats:styled-content>usD binds glucose polysaccharides such as branched laminarin and linear pustulan. The 1.8 Å crystal structure of <jats:styled-content style="fixed-case">GMS</jats:styled-content>usD indicates that three tryptophan residues form the putative glycan‐binding site. Mutagenesis studies confirmed that these residues are crucial for laminarin recognition. We queried metagenomes of global surface water datasets for the occurrence of SusD‐like proteins and found sequences with the three structurally conserved residues in different locations in the ocean. The molecular selectivity of <jats:styled-content style="fixed-case">GMS</jats:styled-content>usD underscores that specific interactions are required for laminarin recognition. In conclusion, our findings provide insight into the molecular details of β‐glucan binding by <jats:styled-content style="fixed-case">GMS</jats:styled-content>usD and our bioinformatic analysis reveals that this molecular interaction may contribute to glucan cycling in the surface ocean.</jats:p>