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).
References:
AvrE (DspE) of 1838 aas and a beta (β) structure after secretion from the bacteriial cytoplasm via a type III protein secretion system (TC# 3.A.6) into the host cell and insertion into the plasma membrane of the plant cell where it transports metabolites, water and small molecules such as fluorescene dyes (Nomura et al. 2023). DspE in Xenopus oocytes resulted in inward and outward currents, permeability to water and osmolarity-dependent oocyte swelling and bursting. 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 dendrimers as inhibitors of the DspE/AvrE channels. Notably, polyamidoamines broadly inhibit AvrE and DspE virulence activities in Xenopus oocytes and during E. amylovora and P. syringae infections.
AvrE of Erwinia amylovora
AvrE of 1795 aas with a beta (β) structure; it inserts into the plant cell membrane after secretion from the bacterium via the type III secretion system (TC# 3.A.6) to form pores (Nomura et al. 2023).
AvrE of Pseudomonas syringae
AvrE-family type 3 secretion system effector of 1625 aas.
AvrE homolog of Dickeya chrysanthemi (Pectobacterium chrysanthemi)
AvrE-family type 3 secretion system effector of 1839 aa
AvrE of Mixta calida
DspE-family type 3 secretion system effector of 1829 aas.
DspE of Pantoea agglomerans pv. gypsophilae (Erwinia herbicola)
AvrE-family type 3 secretion system effector of 1829 aa
AvrE homolog of Brenneria goodwinii
Type III effector protein AvrE1 of 1437 aa
AvrE of Pseudomonas orientalis
AvrE-family type 3 secretion system effector of 1889 aa
AvrE homolog of Pseudomonas quasicaspiana
Averulence protein, DspE of 1614 aas.
DspE (DspA) of Pectobacterium atrosepticum (Erwinia carotovora subsp. atroseptica)