Characterization of the Yam Tuber Storage Proteins from Dioscorea batatas Exhibiting Unique Lectin Activities

Abstract

Four major proteins designated DB1, DB2, DB3, and DB4 were isolated and characterized from the yam tuber Dioscorea batatas. The ratios of their yields were 20:50:20:10. DB1 was a mannose-binding lectin (20 kDa) consisting of 10-kDa subunits and was classified as the monocot mannose-binding lectin family. DB2, accounting for 50% of the total protein, was the storage protein, commonly called dioscorins consisting of a 31-kDa subunit. On the basis of amino acid sequence, DB2 was classified to be dioscorin A. DB3 was a maltose-binding lectin, having an apparent molecular mass of 120 kDa and composed of a 66-kDa subunit and two 31-kDa subunits (DB3S). The 66-kDa subunit was further composed of two 31-kDa subunits (DB3L) cross-linked by disulfide bonds. DB3L and DB3S (242 and 241 amino acid residues, respectively) were homologous with each other with 72% sequence identity. They showed a sequence homology to dioscorin B and dioscorin A from Dioscorea alata, with 90 and 93% identity, respectively, and to carbonic anhydrase from Arabidopsis thaliana with about 45% identity. DB3S had one intrachain disulfide bond located at Cys 28 -Cys 187 , whereas DB3L had one interchain disulfide bond (Cys 40 -Cys 40 ) in addition to the intrachain disulfide bond (Cys 28 -Cys 188 ) to form a 66-kDa subunit. DB1 and DB3 agglutinated rabbit erythrocytes at 2.7 and 3.9 g/ml, respectively. Despite the structural homology between DB2 and DB3, DB2 had no lectin activity. The 66-kDa subunit itself revealed the full hemagglutinating activity of DB3, indicating that DB3L but not DB3S was responsible for the activity. The hemagglutinating activity of DB3 required Ca 2؉ ions and was exclusively inhibited by maltose and oligomaltoses (e.g. maltopentaose and maltohexaose) but not by D-glucose. DB3 could not be classified into any known plant lectin family. DB4 was a chitinase, homologous to an acidic chitinase from Dioscorea japonica. DB1, DB2, and DB3 did not show any activity of carbonic anhydrase, amylase, or trypsin inhibitor activity. These results show that two of the four major proteins isolated from the yam tubers D. batatas have unique lectin activities.

Transgenic technologies in cassava for nutritional improvement and viral disease resistance: a key strategy for food security in Africa

“…The two subclasses (A and B) of dioscorin differ mainly in the presence or absence of a single disulfide bond. The size of dioscorin A and its function as storage protein in yam tubers were confirmed recently [37] . Interestingly, dioscorin has antioxidative properties with radical scavenging activity, equivalent to that of glutathione at similar protein concentrations [38] .…”

Purification, Characterization, and Molecular Cloning of a Novel Antifungal Lectin From the Roots of Ophioglossum pedunculosum

“…of flowering plants, low levels of lectins and related proteins in the [43,44]. It was mentioning that OPA specifically agglutinated human O erythrocytes and rabbit erythrocytes, suggesting that OPA recognized the structure of saccharides comprising the surface of erythrocyte membranes.…”

Mannose-Binding Lectin from Yam (Dioscorea batatas) Tubers with Insecticidal Properties againstHelicoverpa armigera(Lepidoptera: Noctuidae)

“…We isolated and characterized four major proteins designated DB1, DB2, DB3, and DB4 from the yam tuber Dioscorea batatas (21). The ratios of their yields were 20:50:20:10.…”