Insights into the mechanism of membrane fusion induced by the plant defense element, plant-specific insert

Abstract

<jats:p>In plants, many natural defense mechanisms include cellular membrane fusion as a way to resist infection by external pathogens. Several plant proteins mediate membrane fusion, but the detailed mechanism by which they promote fusion is less clear. Understanding this process could provide valuable insights into these proteins’ physiological functions and guide bio-engineering applications, (i.e., the design of antimicrobial proteins). The plant specific insert (PSI) from Solanum tuberosum can help reduce certain pathogen attack via membrane fusion. To gain new insights into the process of PSI induced membrane fusion a combined approach of NMR, FRET and in silico studies was used. . Our results indicate that (<jats:italic>i</jats:italic>) under acidic conditions, the PSI experiences a monomer-dimer equilibrium and the dimeric PSI induces membrane fusion below a certain critical pH; (<jats:italic>ii</jats:italic>) after fusion, the PSI resides in a highly dehydrated environment with limited solvent accessibility, suggesting its capability in reducing repulsive dehydration forces between liposomes to facilitate fusion; and (<jats:italic>iii</jats:italic>) as shown by molecular dynamics simulations, the PSI dimer can bind stably to membrane surfaces, and can bridge liposomes in close proximity, a critical step for the membrane fusion. In summary, this study provides new and unique insights into the mechanisms by which the PSI and similar proteins induce membrane fusion.</jats:p>

Negatively charged phospholipids accelerate the membrane fusion activity of the plant-specific insert domain of an aspartic protease

“…As a potential antimicrobial protein, the PSI's mechanism against the pathogen invasion has attracted much attention ( 5 , 8 , 9 , 10 , 11 ), although much remains unknown. The PSI forms dimers under acidic conditions ( 10 ) and adopts a fold similar to that of saposin-like proteins (SAPLIPs) in mammals ( 12 , 13 ), which generally demonstrate the ability to bind and disrupt membranes ( 14 , 15 , 16 ).…”

“…The PSI forms dimers under acidic conditions ( 10 ) and adopts a fold similar to that of saposin-like proteins (SAPLIPs) in mammals ( 12 , 13 ), which generally demonstrate the ability to bind and disrupt membranes ( 14 , 15 , 16 ). Similar to other SAPLIPs, the PSI interacts with lipid bilayers ( 10 , 15 , 17 ), inducing membrane permeability ( 18 , 19 ) and membrane fusion ( 5 , 11 ). Using vesicles with different lipid compositions, the PSI's ability to induce membrane fusion was pH dependent ( 10 , 11 ).…”

“…Similar to other SAPLIPs, the PSI interacts with lipid bilayers ( 10 , 15 , 17 ), inducing membrane permeability ( 18 , 19 ) and membrane fusion ( 5 , 11 ). Using vesicles with different lipid compositions, the PSI's ability to induce membrane fusion was pH dependent ( 10 , 11 ).…”

PSI relieves the pressure of membrane fusion

“…To gain a more holistic view of the PSI-catalyzed membrane fusion mechanism, Zhao et al report an elegant integration of biophysical experiments, notably NMR, and molecular dynamics simulations to reveal the cascade of events leading up to PSI-mediated membrane fusion (2). They used a clever approach that directly links vesicle fusion to fluorescence to investigate pH variations on the rate and extent of PSI-mediated fusion.…”

“…Acknowledgments-I thank Zhao et al (2) for providing the trajectory files from their coarse-grained simulations, some of which were used to prepare Fig. 1C.…”