TRPP subunits can be divided into two subcategories depending on structural similarity.
The first group, TRPP1-like, contains TRPP1, PKDREJ, PKD1L1, PKD1L2, and PKD1L3. TRPP1 contains numerous N-terminal adhesive domains that are important for cell-cell contact. This group of subunits also contain a large extracellular domain with numerous polycystin motifs. These motifs are of unknown function and are located between the S6 and S7 segments. The large intracellular C-terminal segment of TRPP1 seems to interact with TRPP2 to act as a signaling complex.
The other group of TRPP members are TRPP2-like: TRPP2, TRPP3, and TRPP5. Unlike the TRPP1-like group, which contain 11 membrane-spanning segments, the TRPP2-like group resemble other TRP channels, having 6 membrane-spanning segments with intracellular N- and C-termini. All of the members of this group contain a coiled coil region in their C-terminus involved in the interaction with the TRPP1-like group. TRPP2 and TRPP3 form constitutively active cation-selective ion channels that are permeable to calcium. TRPP3 has also been implicated in sour taste perception. Coupling of TRPP1 and TRPP2 recruits TRPP2 to the membrane. Here, its activity is decreased and it suppresses the activation of G proteins by TRPP1.