The 3 types of interactions and their subtypes, a total of 8 interactions. A. A schematic diagram for the locations of the 3 types of contacts in the PIDD DD: RAIDD DD complex. B. The 3 different subtypes of the type I interaction. C. The 2 different subtypes of the type II interaction. D. The 3 different subtypes of the type III interaction. Important residues and hydrogen bonding interactions are labeled. E. A hypothetical Fas DD: FADD DD complex constructed from the same 3 types of interactions. The same view is used as in A and the Fas DD: FADD DD complex may be considered as a portion of the PIDD DD: RAIDD DD complex composed of R7, R2, P2, R3, P3 and R4.