SUL-I and SUL-II from the large flower-like globiferous pedicellariae of T. pileolus are D-galactose-specific lectins with molecular masses 32 kDa and 23 kDa, respectively (Nakagawa et al., 1996, 1999b). On the other hand, TGL-I from the small globiferous pedicellariae of T. gratilla is a heparin-specific lectin with a molecular mass of 23 kDa (Nakagawa et al., 1999a). SUL-I induced mitogenic stimulation on murine splenocytes in lower dose ranges such as 0.5 μg/ml. At higher doses SUL-I had an inhibitory effect on the splenocytes. However, SUL-II and TGL-I did not induce significant activity on the splenocytes as shown in Figure 2.

　

Further studies of biological activities of SUL-II and TGL-I are in progress for comparison with those of SUL-I. More recently, we found that Contractin A, a mannose-containing glycoprotein (18 kDa) (Nakagawa et al., 1991) is a novel lectin that causes smooth muscle contraction and relaxation. Contractin A also induced mitogenic stimulation on murine splenocytes (data not shown). The dual response to SUL-I was effectively inhibited by 50 mM D-galactose (data not shown). Thus, the data suggest that SUL-I may exhibit mitogenic and inhibitory activities through binding to D-galactose containing carbohydrates that are present on the surface of murine splenocytes. Moreover, it has been suggested that SUL-I binds to D-galactose residues of Datura stramonium agglutinin (DSA) to interfere with mast cell activation induced by DSA, a glycoprotein with arabinose and D-galactose residues (Suzuki-Nishimura et al., 2001). Our previous finding revealed that SUL-I induces chemotactic activity of guinea-pig neutrophils (Nakagawa et al., 1996).

　

In the present study, the chemotactic and phagocytic responses to SUL-I were also examined on guinea-pig macrophages. SUL-I had chemotactic and phagocytic activities for guinea-pig macrophages in dose dependent manner (Fig.3). In human polymorphonuclear leukocytes SUL-I exhibited chemotactic activity (data not shown). Chemotaxis and phagocytosis by leukocytes play an important role in the defense reactions to infection and injury in higher vertebrates. Thus, it is interesting that SUL-I as a chemoattractant may be a useful tool for biomedical research. Sequence analysis of intact SUL-I indicated N-terminal sequence from Ala-I to Ile-35 (Nakagawa et al., 1999b). SUL-I shows five glycine residues in the sequence region. SUL-II was subjected to partial amino acid sequence analysis. The sequence of 21 residues from the N-terminal was established. The N-terminal amino acid is serine. SUL-II is rich in serine (Table 1). Although SUL-II did not show a sequence homology to SUL-I, it was found to be 45% and 40% homologous to the sequence of Contractin A (Nakagawa et al., 1991) and UT841 from T. pileolus (Zhang et al., 2001), respectively. SUL-II, Contractin A and UT841 may be a phospholipase A₂-like substance, because there is a good relationship to the amino acid sequence of phospholipase A₂ (Takasaki et al., 1990).

　

On the other hand, SUL-I is related to the segment Tyr-Gly-Arg of the rhamnose-binding lectins (SAL and STL2) from fish eggs (Tateno et al., 1998; Hosono et al., 1999). Although physiological roles of multiple lectins from the toxopneustid sea urchins are not well understood, our data suggest an extracellular function for SUL-I and Contractin A that may have wide-ranging effects, and suggest that these lectins can be used as valuable tool for analysis of inflammation, differentiation and development of cells. Further structural studies on SULs, Contractin A and TGL-I are needed to elucidate the biological functions of sea urchin venoms.

　

　

　

We would like to thank Professor K. Ohura and Dr. M. Shinohara, Osaka Dental University, for measuring chemotaxis and phagocytosis. We are also grateful to Professor Y. Tomihara and Dr. Y. Araki for their constant interest in this work, and Mr. H. Nada and Mr. H. Nagata for collection of sea urchins.

　

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