New cell surface lectins with complex carbohydrate specificity from cyanobacteria

Abstract

Lectins, proteins mainly of plant origin, possess anti-HIV, anti-inflammatory, antimicrobial, antinociceptive, antiproliferative, antitumour and antiviral properties. Further, they are useful tools in biomedical research, have potent mitogenic potential, and also play a vital role in various biological processes, particularly in host defense mechanisms. The beneficial nature of lectins is often attributed to their ability to agglutinate cells through sugar-specific binding sites. Here, we screened cyanobacterial species for occurrence of surface bound lectins and evaluated their carbohydrate specificity. Eleven cyanobacterial species were screened for lectins using human, pig, sheep, goat and rabbit erythrocytes. Amongst them, only five organisms, namely <i>Anabaena naviculoides </i> RFKK3, <i>Anabaena torulosa </i> RFGB5, <i>Anabaena variabilis</i> RFTM22, <i>Desmonostoc muscorum </i> RFKK18 and <i> Synechocystis </i> sp. RFDB50 were found to possess cell surface lectins. These lectins showed non-specific agglutination towards animal (rabbit, pig, sheep and goat) and human (ABO) erythrocytes. Neuraminidase treated human blood type-O erythrocytes enhanced the lectin activity of <i>Anabaena naviculoides </i> RFKK3, <i>Anabaena torulosa </i> RFGB5, <i>Anabaena variabilis </i> RFTM22, <i>Desmonostoc muscorum </i> RFKK18, while protease treated human blood type-O erythrocytes enhanced the lectin activity of only <i>Anabaena variabilis </i> RFTM22 and <i> Desmonostoc muscorum </i> RFKK18. Lectin activity of <i>Synechocystis</i> sp. RFDB50 remained unaltered with enzymatically treated human blood type-O erythrocytes. A panel of sugars were tested for inhibition of lectin activity. Lectins from majority of the test organisms were found to be inhibited by glycoproteins, bovine submaxillary mucin and porcine stomach mucin. Simple sugars and derivatives were non-inhibitory towards <i>Anabaena variabilis</i> RFTM22 lectin activity. This indicates that cyanobacterial lectins possess unique glycoprotein binding specificities. <i>Anabaena naviculoides</i> RFKK3 and <i>Anabaena torulosa</i> RFGB5 cultures showed maximum lectin activity during log phase of growth. <i>Anabaena variabilis</i> RFTM22 and <i>Desmonostoc muscorum</i> RFKK18 cultures expressed maximum lectin activity during stationary phase of growth. However, <i>Synechocystis </i> sp. RFDB50 expressed lectin activity only during log phase of growth. Literature survey reveals, this is the first report on cell surface lectins from cyanobacteria.