Structural selleck Vorinostat and functional features distinguish eight to fifteen lectin groups largely related to immunity, C type, S type or glycan binding galectins, I type specific to sialic acids and glycoseaminoglycans also containing an Ig like fold, pentraxins, fucolectins, fibrinogen like lectins, ficolins, tachylectins and slug agglutinin, chitinase like lectins, and orphan lectins. Transmembrane calnexins and solu ble calreticulins support trafficking, sorting and matura tion of glycoproteins whereas lectins localized in the plasma membrane or released into the extracellular matrix and body fluids mediate a broad range of pro cesses including cell adhesion, cell signalling, pathogen recognition and endocytosis.

Compared to more ancient lectins acting in the quality control of glycoproteins, extracellular lectins such as ficolins have evolved inde pendently in the vertebrate and invertebrate lineages. The evolutionary radiation of these molecules d lec tin ligand interactions in the immune responses and apoptotic cell clearance. Table 2 summarizes in decreasing abundance the lec tin like sequences identified in Mytibase by searching archetype lectin domains. A total of 148 MGCs share the descriptive term lectin as Interpro key word. The most abundant and heterogeneous group refer to C type lectins originally named to reflect the importance of Ca in sugar binding. Many are similar to the nacre protein perlucin from Haliotis laevigata, while others remind of mammalian pro teoglycans, type II receptors expressed particularly on macrophages and dendritic cells.

For instance, among 9 MGCs the consensus MGC04167 is the most similar to the macrophage mannose receptor, protein involved in the glycoprotein endocytosis and antigen presenta tion, whereas 13 MGCs display similarity to the human DC SIGN CD209 antigen. Regardless of some con served residues the remark able sequence diversity of the C type lectins expressed in mussels confirms them as candidate PRR. As a matter of fact, many of the Caenorhabditis elegans proteins containing a C type lectin domain support pathogen specific responses. The second abundant lectin like group recalls fibrino gen and fibronectin proteins and ficolins. Like the CRD of the mannose binding lectins, the C terminal fibrino gen like domain of ficolins has a bouquet like structure which binds the carbohydrate residues of foreign and apoptotic cells or in associa tion with specific Brefeldin_A serine proteases initiates the pro teolytic complement cascade and pathogen lysis. Species specific expansion of fibrinogen related proteins has been reported in the snail Biomphalaria glabrata and the mosquito Anopheles gambiae.