Cloning and characterization of a lectin from the octocoral Sinularia lochmodes Mitsuru Jimbo a, * , Kazuhiko Koike a , Ryuichi Sakai a , Koji Muramoto b , Hisao Kamiya a a Department of Marine Biosciences, School of Fisheries Sciences, Kitasato University, Oofunato, Iwate 022-0101, Japan b Department of Molecular Life Science, Graduate School of Life Sciences, Tohoku University, Sendai, Miyagi 981-8555, Japan Received 16 February 2005 Abstract In the present study, the entire amino acid sequence and cDNA structure encoding the D-galactose-binding lectin, SLL-2, isolated from the octocoral Sinularia lochmodes, were determined. SLL-2 regulates the morphology of symbiotic dinoflagellates Symbiodi- nium spp. through unknown mechanisms. Here, three cDNAs that encode SLL-2 were cloned and characterized. All the SLL-2 cDNAs encoded 142 amino acids with high similarity to each other. The mature subunit of SLL-2 was found to be composed of 94 amino acids and to contain one putative glycosylation site common to all three SLL-2. N-Glycopeptidase F treatment of SLL-2 resulted in a protein band shift from 16.5 to 9.5 kDa in SDS–PAGE, confirming that SLL-2s are glycoproteins. Two-dimen- sional polyacrylamide gel electrophoresis analysis of the deglycosylated SLL-2 indicated a presence of three polypeptides as encoded in SLL-2 cDNAs. The deduced sequences of SLL-2 cDNAs had a similarity to the C-terminal region of discoidin I, the slime mold Dictyostelium discoideum lectin. Ó 2005 Elsevier Inc. All rights reserved. Keywords: Octocoral; Sinularia lochmodes; D-Galactose-binding lectin; Discoidin; Symbiotic dinoflagellates; Symbiosis; Symbiodinium A number of lectins, carbohydrate-binding proteins, are known to be present in a variety of animals and plants, and their roles in various biological processes have been characterized. In marine animals, lectins, especially invertebrate humoral lectins, are believed to contribute as non-self recognition factors to the defense mechanism [1,2]. Moreover, there is a collective body of evidence supporting that marine invertebrate lectins are also involved in various endogenous biological events such as biomineralization [3] and embryonic develop- ment [4–6]. Interestingly, it has been theorized that some marine animal lectins mediate the interaction between symbiont and host. For example, a lectin isolated from the marine sponge Halichondria panacea has been re- ported to have a growth-promoting effect on symbiotic bacteria Pseudomonas insolita [7]. It has also been pro- posed that the symbiosis between the tunicate Didem- num molle and the microalga Prochloron sp. is also mediated by D. molle lectins [8]. Tridacnin, a mitogenic D-galactose-binding lectin that is present in the hemo- lymph of the giant clam Tridacna maxima, reacts with various galactans, which are constituents of symbiotic algae, and is regarded as essential for elimination and utilization of their symbionts, which have exposed galac- tan structures on their surface during degeneration [9]. It has also been reported that glycoprotein or glycoconju- gate on the symbiont surface is important in symbiont acquisition by hosts, since glycosidase or lectin treat- ment of symbiont surface showed ill effects on the acqui- sition [10–12]. These observations strongly suggest the presence of a chemical substance, which mediates the establishment of symbiosis between symbiotic algae and host. We previously isolated a D-galactose-binding lectin, SLL-2, from the octocoral Sinularia lochmodes and found that the lectin was distributed densely on 0006-291X/$ - see front matter Ó 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2005.02.137 * Corresponding author. Fax: +81 192 44 3932. E-mail address: mjinbo@kitasato-u.ac.jp (M. Jimbo). www.elsevier.com/locate/ybbrc Biochemical and Biophysical Research Communications 330 (2005) 157–162 BBRC