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 (28,021.5Da), 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.