Beta Sheets in the 3D Structure of the Concanavalin A (Con A) Monomeric Subunit

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The protein on the right helps illuminate some of the biologically significant features of β-sheets. This protein is the monomeric subunit (26 kDa) subunit of a Con A, a homotetramic plant lectin in the seeds of Jack beans (Canavalia ensiformis) that functions as a carbohydrate-binding protein with specificity for mannose and other carbohydrate hexamers. In the absence of a sugar ligand, two metal ions -- one manganese ion (Mn, orange sphere) and one calcium ion (Ca, white sphere) -- are chelated to water molecules (H2O, redorange) in the carbohydrate binding site, which are displaced on binding to sugar moieties, even those linked to complex polysaccharide structures. For example, tetrameric Con A can physically agglutinate cells by cross-linkg cell surface mannose-containing polysaccharides on different cells, and in this regard,Con A is said to act as an agglutinin.

The structure of Con A is striking in that so much of the polypeptide backbone of is folded into β-sheets econdary structure (represented by the flat arrows heads in this image) with little evidence for the presecne of other secondary structures.

Explore the properties of β-sheet secondary structures 0f Con A with the buttons below the image.