A computer model of dianthin 30, a type 1 ribosome-inactivating protein (RIP), is constructed by homology modeling using two known X-ray structures; a type 1 RIP, pokeweed antiviral protein (PAP), and chain A of a type 2 RIP, ricin. The 3D structure is refined by molecular dynamics and its binding site compared with those of PAP and ricin using molecular electrostatic potential mapping. The differences in the maps obtained clearly show how, despite the similarity of the topology of the binding site, differences in electrostatic potential can account for the experimentally observed differences in substrate recognition and binding. This demonstrates the potential of these techniques for guiding further experimental analyses.