1.B.165.  The AvrE/DspE Porin (A/D-P) Family 

AvrE/DspE-family effectors are exported from pathogenic bacteria via a Type III Secretion System (TC# 3.A.6), then once inside the target plant or animal cell, folds into a β-barrel structure that resembles bacterial porins and inserts into the plasma membrane of the cell. Expression of AvrE and DspE in Xenopus oocytes results in (i) inward and outward currents, (ii) permeability to water and (iii) osmolarity-dependent oocyte swelling and bursting (Nomura et al. 2023). Liposome reconstitution confirmed that the DspE channel alone is sufficient to allow the passage of small molecules such as fluorescein dye. Targeted screening of chemical blockers based on the predicted pore size (15-20 Å) of the DspE channel identified polyamidoamine (PAMAM) dendrimers as inhibitors of the DspE/AvrE channels. Remarkably, PAMAMs broadly inhibit AvrE/DspE virulence activities in Xenopus oocytes and during Erwinia amylovora and Pseudomonas syringae infections. Thus, Nomura et al. 2023 have unraveled the enigmatic function of a centrally important family of bacterial effectors with significant conceptual and practical implications in the study of bacterial pathogenesis.

The transport reactions catalyzed by members of the AvrE/DspE Porin (A/D-P) Family are:

water and small molecules (in) ⇌ water and small molecules (out).