Isolectin B4 (IB4) is one of a family of five alpha-D-galactose-binding lectins from Griffonia (Bandeiraea) simplicifolia. Recombinant IB4* was expressed in E. coli and purified using affinity chromatography. In one important application rIB4-SAP specifically eliminates the IB4-positive c-fiber nociceptor neurons, while sparing the peptidergic neurons. Upon binding the alpha-D-galactopyranoside residues expressed on the cell surface, rIB4-SAP becomes internalized and saporin inhibits protein synthesis, resulting in elimination of the neurons. The cytotoxin is extremely potent, with an ED50 in the low picomolar range for some alpha-D-galactopyranoside-expressing cells in vitro. rIB4-SAP is an excellent tool for the study of pain transmission and the biological roles of IB4+ cells in vivo.
IB4-SAP is a chemical conjugate of recombinant IB4 expressed in E. coli and the ribosome-inactivating protein, saporin. IB4-SAP eliminates α-D-galactosyl-positive cells.