Legume lectin

R. Loris, T. Hamelryck, J. Bouckaert, and L. Wyns, Legume lectin structure, Biochim. Biophys. Acta, 1383 (1998) 9-36. 

The lectins can be conveniently divided into the legume (Fabaceae family) and nonlegume proteins. The legume lectins are exemplified by the homodimeric or homo-tetrameric, Ca2+- and Mn2+-binding and mitogenic protein concanavalin A (jackbean phytagglutinin) from Canavalia ensiformis that binds Man, Glc and Man-al-Me. 

B. Shaanan, H. Lis, and N. Sharon. 1991. Structure of a legume lectin with an ordered /V-linked carbohydrate in complex with lactose Science 254 862-866. (PubMed)... 

T. cruzi fran -sialidase first named SARA ( Shed-Acute-Phase-Antigen ) and found in human serum in Chagas disease, is also unique from an immunological aspect, since it contains two immunologically distinct domains and seems to be a naturally chimeric protein having functionally independent enzymatic and antigenic domains [823]. (It is thus reminiscent of V. cholerae sialidase which consists of a catalytic domain and a non-catalytic sequence similar to those of legume lectins [768,791].)... 

The D. biflorus lectin consists of two isolectins, A and B, separable by fractionation on concanavalin A-Sepharose [150]. Each isolectin consists of distinct subunits lA and IIA in form A and IB and IIB in form B. The first 30 NH2-terminal amino acids of lA and IIA are identical but differ at their carboxyl ends [151]. The D. biflorus lectin has been cloned, thus establishing its primary structure [152]. By equilibrium dialysis, it was established that the D. biflorus lectin has two carbohydrate binding sites per molecule for A -acetylgalactosamine. Similar to other legume lectins, the D. biflorus lectin is a metalloprotein, requiring Ca for its activity. 

UEA I has been sequenced and shown to exhibit extensive homology with many other legume lectins, but not with Lotus tetragonolobus, another L-fucose-binding lectin. 

Lectins are another class of potential antinutrient soy proteins (Sharon Lis, 1972 Liener, 1974). The carbohydrate content and structure of soy lectins were determined (Lis Sharon, 1978) and consist of mannose and Af-acetyl-glucosamine at about 5% by weight. Soy lectin has MW 110 kD from four identical subunits. The soy lectins are partly responsible for weight loss in rodent feeding studies with raw soy protein. Soy lectins are relatively easy to heat denature compared to other legume lectins. Properly processed soy foods have little native lectin present. Soybean lectins are widely used in clinical studies because of their interaction with red blood cell surface features (Friedman Brandon, 2001). 

Two conserved residues, Asp and Asn that coordinate Ca to the protein, also form hydrogen bonds with the saccharide in the combining site of legume lectins. The two residues have an identical spatial disposition in these lectins. However, the saccharide is rotated so that a different set of OH s is involved in their interactions, i.e. the 4- and 3-OH s of Gal versus the 4- and 6-OH s of Man. 

These proteins occur in the seeds of many plants but are especially common in the Fabaceae (Leguminosae) (more than 600 species) and the Euphorbiaceae (lectins also occur in other organisms such as fungi, bacteria, and animals). In legumes, lectins are usually found in the cotyledons (Liener, 1991). Well-known plant lectins are concanavalin A, from jack beans Canavalia ensiformis), favin, from the broad bean (Vida faba), and phasin, from the kidney bean (Phaseolus vulgaris) (Ramshaw, 1982), The toxicity of lectins differs considerably (Liener, 1991 Liener et al, 1986). Data for lectins are given in Liener et al. (1986) and Lis and Sharon (1981). 

After cooking or dry heating, the activities of legume lectins and the associated toxic effects are destroyed. After heating to 100 °C for 10 minutes, e. g., soybeans were free of lectin activity. However, the lectins in some legumes are much more stable. 

---