The family of metazoan metal-independent β-galactoside-binding lectins: structure, function and molecular evolution

Abstract

Animal metal-independent beta-galactoside-binding lectins were initially found in vertebrates, but they have recently been isolated from much lower invertebrates, such as nematode and sponge, as well. Further, an eosinophilic lysophospholipase associated with various inflammatory reactions was very recently found to be a new member of this protein family. It appears that beta-galactoside-binding lectins and some non-lectin proteins form a superfamily whose members are widely distributed from vertebrates to invertebrates. From the viewpoints of protein architecture, the superfamily members can be subdivided into three types; i.e. 'proto type' (the relatively well-studied 14 kDa lectins), 'chimera type' (29-35 kDa lectins also known as epsilon BP/CBP35/Mac2/laminin-binding protein) and 'tandem-repeat type' (a newly found nematode 32 kDa lectin). Comparison of their amino acid sequences and mutagenesis studies have suggested the functional importance of some conservative hydrophilic residues (His44, Asn46, Arg48, Glu71 and Arg73 of human 14 kDa lectin). Several non-charged residues (Gly14, Phe45, Pro47, Phe49, Val59, Trp68, Pro78 and Phe79) are also well conserved, and are probably important to maintain the structural framework of these proteins. A consideration of molecular evolution suggests that lectins belonging to this family probably existed in the Precambrian era. Ubiquitous occurrence of these homologous lectins with shared sugar specificity suggests that they are involved in 'essential minimum' functions of multicellular animals, possibly in cooperation with their partner glycoconjugates.

Developmental regulation, expression, and apoptotic potential of galectin-9, a beta-galactoside binding lectin.

“…Mammalian lectins are classified into four categories, C-type lectins (including selectins), P-type lectins, pentraxins, and galectins (2,3). Galectins seem to be highly conserved, since they have been found in animals low in the evolutionary phylogeny, including poriferans and nematodes (4,5). To date, 10 members of lactose binding mammalian galectins have been cloned, sequenced, and functionally characterized, and they include galectin-1 (6), -2 (7), -3 (8), -4 (9), -5 (10), -6 (10), -7 (11,12), -8 (13), -9 (14), and -10 (15-17).…”

Galectin-1 is essential in tumor angiogenesis and is a target for antiangiogenesis therapy

“…gal-1 belongs to a family of carbohydrate-binding proteins that share a conserved carbohydrate recognition domain of Ϸ130 aa (7)(8)(9). Over a dozen mammalian galectins have been described (10,11), and members of this family are expressed in a wide range of species, suggesting an important role for galectins in basic cellular mechanisms.…”

Identification and Characterization of a Chitin-binding Protein Purified from Coelomic Fluid of the Lugworm Arenicola marina Defining a Novel Protein Sequence Family

“…Several lectins with carbohydrate-recognizing domains of C-type (calciumdependent) lectins have been found in tunicates, echinoderms, and arthropods (7)(8)(9)(10). Galectins (calcium-independent galactose-specific lectins) have been detected in annelids (11,12), nematodes (13)(14)(15), and sponges (16,17). Fibrinogen-related domains (FReDs or FRePs) with lectin activity are found in mammalian lectins, such as the ficolins, and in invertebrates (18 -20).…”