Biological activity, cDNA cloning and primary structure of lectin KSA-2 from the cultivated red alga Kappaphycus striatum (Schmitz) Doty ex Silva

Abstract The red alga ( Kappaphycus striatum ) has been widely cultivated as a source of carrageenophytes for industry. Previously, lectin KSA-2 from this alga has been isolated and evaluated for the strictly high-mannose N -glycan binding specificity. In this study, we have determined the antibacterial activities and cDNA cloning encoding lectin KSA-2. Complementary DNA (cDNA) cloning based on the rapid amplification of cDNA ends (RACE) elucidated the full-length sequence of KSA-2, which encoded a polypeptide of 269 amino acids including initiating methionine, with four tandemly repeated domains of about 67 amino acids, and sharing 45% sequence identity. The calculated molecular mass from the deduced sequence was consistent with that of natural KSA-2 (28,021.5 Da), which was determined by electron spray ionization–mass spectrometry. The primary structure of KSA-2 is highly similar to those of the high-mannose N -glycan specific lectins in lower organisms including Burkholderia oklahomensis EO147 (BOA), Myxococcus xanthus (MBHA) and Pseudomonas fluorescens Pf0-1 (PFL) from proteobacteria, Oscillatoria agardhii NIES-240 (OAA) from cyanobacterium, Eucheuma serra (ESA-2) and Eucheuma denticulatum (EDA-2) from macro red algae, indicating that they were closely related to each other. The active fraction KSA-2 inhibited the growth of human and shrimp pathogenic bacteria Enterobacter cloacae and Vibrio alginolyticus , respectively, although it did not affect the growth of Staphylococcus aureus , Escherichia coli , Vibrio parahaemolyticus and Vibrio harveyi , suggesting that KSA-2 caused the activity through binding to the target receptor(s) on the cell surface of E. cloacae and V. alginolyticus . These results indicate that the cultivated K. striatum is a good source of a lectin that may be useful as an antibacterial agents.