ABSTRACT
C-type lectins can be classified into groups based on their domain architectures and structural features (Drickamer, 1993; Drickamer and Dodd, 1999; Dodd and Drickamer, 2001; Drickamer and Fadden, 2002; Zelensky and Gready, 2004). Most vertebrate C-type lectins contain a single carbohydrate recognition domain (CRD) connected to other types of domains or motifs (Drickamer, 1993). For example, mannose-binding lectin (MBL), also called mannose-binding protein (MBP), a member of the collectin subgroup, contains a single CRD connected to a collagenlike domain (Holmskov et al., 2003). Some mammalian C-type lectins, such as the macrophage mannose receptor, contain multiple CRDs, but not all of the CRDs are functional for carbohydrate binding (East and Isacke, 2002). In invertebrates, including insects, multiple genes encoding C-type lectin like domains (CTLDs) have been identi ed in the nematode Caenorhabditis elegans, the fruit y Drosophila melanogaster, and the mosquito Anopheles gambiae (Drickamer and Dodd, 1999; Dodd and Drickamer, 2001; Christophides et al., 2002). C-type lectins have also been isolated from other insect and arthropod species. Invertebrate C-type CRDs have an overall low similarity in amino acid sequence (less than 30% identity) to mammalian C-type
CRDs. A group of C-type lectins from arthropods containing dual or tandem CRDs has been named immulectins (IMLs). These dual-CRD lectins have been found in several Lepidopteran species, including Manduca sexta (Yu et al., 1999, 2005, 2006; Yu and Kanost, 2000), Bombyx mori (accession number: AY297159; Koizumi et al., 1999; Watanabe et al., 2006), Hyphantria cunea (Shin et al., 1998), Helicoverpa armigera (accession number: ABF83203), Lonomia oblique (accession number: AAV91450), and the Chinese shrimp Fenneropenaeus chinensis (Liu et al., 2007). The unique dual-CRD architecture has not been found in Dipteran insects such as D. melanogaster and A. gambiae, or mammals. But genes encoding dual-CRD C-type lectins are present in C. elegans and the sh Fugu rubripes (Drickamer and Dodd, 1999; Zelensky and Gready, 2004). Members of the lepidopteran immulectin family contain an amino-terminal short form CRD1, which is structurally similar to the CRD of MBL and stabilized by two pairs of disul de bonds, and a carboxyl-terminal long form CRD2 that is more similar to CRD4 of the macrophage mannose receptor and contains three pairs of disul de bonds (Yu and Kanost, 2000) (Figure 26.1).
