2.A.69.1.4
Auxin efflux facilitator PIN3: functions in auxin redistribution through the root cap in response to the gravity sensors, ARL2 (Q6XL73) and ARG1 (Q9ZSY2). Both ARG1 and ARL2 are DnaJ homologues and show regions homologous to translocation proteins, NPL1 and Sec63 (3.A.5.8.1 and 3.A.5.9.1, respectively). Cryo-EM structures of AtPIN3 in the apo state and in complex with its substrate indole-3-acetic acid (IAA) and the inhibitor N-1-naphthylphthalamic acid (NPA) at 2.6-3.0 Å resolution have been determined (Su et al. 2022). AtPIN3 exists as a homodimer, with TMSs 1, 2, and 7 in the scaffold domain involved in dimerization. The dimeric AtPIN3 forms a large, joint extracellular-facing cavity at the dimer interface while each subunit adopts an inward-facing conformation. The structural basis for the recognition of IAA and NPA were revealed and elucidated the molecular mechanism of NPA inhibition. The AtPIN3 structures support an elevator-like model for the transport of auxin, whereby the transport domains undergo up-down rigid-body motions and the dimerized scaffold domains remain static (Su et al. 2022). CslPIN3 is involved in the regulation of root growth and development as well as auxin accumulation in tea plants (Hu et al. 2023).