Structural characterization and bacterial agglutination of a new OAAH-type lectin from the marine red alga Amansia multifida J.V. Lamouroux

Abstract Lectins are carbohydrate-binding proteins involved in diverse biological processes and with increasing relevance in biotechnological applications. In this study we report the structural characterization of a lectin from the marine red alga Amansia multifida (AML). Mass spectrometry analysis revealed two major isoforms with molecular masses of 28,388 Da and 28,661 Da. The primary structure of a lectin with a molecular weight of 28,661 Da was determined by combination of N-terminal Edman degradation, tandem mass spectrometry, and RACE-PCR, revealing four tandemly repeated domains and high sequence identity with members of the OAAH ( Oscillatoria agardhii agglutinin homologous) lectin family. Notably, A. multifida belongs to the order Ceramiales, suggesting a broader taxonomic distribution for this lectin family, previously restricted to species from the order Gigartinales. Secondary and tertiary structure analyses suggested a predominantly β-sheet conformation and a β-barrel fold, characteristic of OAAH lectins. Molecular docking showed conserved recognition of mannosylated glycans, supported by the presence of the QWGGREGPI motif in all carbohydrate recognition domains. Although AML did not exhibit direct antibacterial or antibiofilm activity, it was able to agglutinate Escherichia coli and Staphylococcus aureus strains, indicating potential interactions with mannoside-rich surface glycans. These findings enhance our understanding of marine lectin diversity and highlight AML as a new lectin of OAAH family.