An isolated RBP with at least one of the following characteristics:

• a) a molecular weight of approximately 65-70 kDa and more preferably 66-69 kDa;
• b) a pl of greater than 10 or less than 3;
• c) a dissociation constant of approximately 1.510^-;6 when bound to the rhamnose moiety of solamargine;
• d) adapted to bind to a rhamnose affinity column prepared according to example 1 and under the conditions set out therein;
• e) adapted to be eluted from the column in example 1 with a 100 mM rhamnose solution;
• f) insoluble in aqueous solution; and
• g) soluble in highly denaturing buffers containing greater that approximately 2% surfactant.