| Abstract | Lectins and glucanases exhibit the common property of reversibly binding to specific complex carbohydrates. The lectins/glucanases are a diverse group of proteins found in a wide range of species from prokaryotes to humans. The different family members all contain a concanavalin A-like domain, which consists of a sandwich of 12-14 beta strands in two sheets with a complex topology. Members of this family are diverse, and include the lectins: legume lectins, cereal lectins, viral lectins, and animal lectins. Plant lectins function in the storage and transport of carbohydrates in seeds, the binding of nitrogen-fixing bacteria to root hairs, the inhibition of fungal growth or insect feeding, and in hormonally regulated plant growth [ 9094437]. Protein members include concanavalin A (Con A), favin, isolectin I, lectin IV, soybean agglutinin and lentil lectin. Animal lectins include the galectins, which are S-type lactose-binding and IgE-binding proteins such as S-lectin, CLC protein, galectin1, galectin2, galectin3 CRD, and Congerin I [11834744].
Other members with a Con A-like domain include the glucanases and xylanases. Bacterial and fungal beta-glucanases, such as Bacillus 1-3,1-4-beta-glucanse, carry out the acid catalysis of beta-glucans found in microorganisms and plants [7589539]. Similarly, kappa-Carrageenase degrades kappa-carrageenans from marine red algae cell walls [11435116]. Xylanase and cellobiohydrolase I degrade hemicellulose and cellulose, respectively [9618460, 9466911].
There are many Con A-like domains found in proteins involved in cell recognition and adhesion. For example, several viral and bacterial toxins carry Con A-like domains. Examples include the Clostridium neurotoxins responsible for the neuroparalytic effects of botulism and tetanus [10932256]. The Pseudomonas exotoxin A, a virulence factor which is highly toxic to eukaryotic cells, causing the arrest of protein synthesis, contains a Con A-like domain involved in receptor binding [11734000]. Cholerae neuraminidase can bind to cell surfaces, possibly through their Con A-like domains, where they function as part of a mucinase complex to degrade the mucin layer of the gastrointestinal tract [7922030]. The rotaviral outer capsid protein, VP4, has a Con A-like sialic acid binding domain, which functions in cell attachment and membrane penetration [11867517].
Con A-like domains also play a role in cell recognition in eukaryotes. Proteins containing a Con A-like domain include the sex hormone-binding globulins which transport sex steroids in blood and regulate their access to target tissues [10675319], laminins which are large heterotrimeric glycoproteins involved in basement membrane architecture and function [10747011], neurexins which are expressed in hundreds of isoforms on the neuronal cell surface, where they may function as cell recognition molecules [10520997] and sialidases that are found in both microorganisms and animals, and function in cell adhesion and signal transduction [12419220].
Other proteins containing a Con A-like domain include pentraxins and calnexins. The pentraxin PTX3 is a TNFalpha-induced, secreted protein of adipose cells produced during inflammation [12611905]. The calnexin family of molecular chaperones is conserved among plants, fungi, and animals. Family members include Calnexin, a type-I integral membrane protein in the endoplasmic reticulum which coordinates the processing of newly synthesized N-linked glycoproteins with their productive folding, calmegin, a type-I membrane protein expressed mainly in the spermatids of the testis, and calreticulin, a soluble ER lumenal paralog [11583625].
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