Structure of the defensin NsD7 in complex with PIP₂ reveals that defensin : lipid oligomer topologies are dependent on lipid type

Abstract

Defensins are innate immune molecules that upon recognition of specific phospholipids can disrupt microbial membranes by forming oligomeric assemblies. Structures of two related plant defensins, NaD1 and NsD7, bound to phosphatidylinositol 4,5-bisphosphate (PIP ) and phosphatidic acid (PA), respectively, revealed striking differences in their oligomeric topologies. To understand how NsD7 binds different phospholipids and rationalize the different topologies, we determined the structure of an NsD7-PIP complex. This structure reveals fundamental differences in phospholipid binding compared to NsD7-PA, and an oligomeric topology nearly identical to the previously determined NaD1-PIP complex, establishing that the PIP fibril topology is conserved between NaD1 and NsD7. Our findings highlight the remarkable ability of defensins to bind different types of phospholipids to form oligomeric fibrils with diverse topologies.

Plant Antibacterial Peptides and their Possible Oligomerization

“…Different authors have suggested several mechanisms for permeabilization of membranes [9,30]. In recent years some of the oligomeric structures of plant AMPs bound to their membrane target have been reported and their structures were deposited in the Protein Data Bank [20,[31][32][33]. We found that most of the peptides in our dataset were predicted to have at least one amyloidogenic region which strengthens our belief that these regions could help the AMPs to form oligomers.…”

X-ray structure of a carpet-like antimicrobial defensin–phospholipid membrane disruption complex

“…An understanding of the mechanism by which CAPs such as defensins are able to cause membrane permeabilization and cell death is important for their development as antimicrobial and antitumor molecules. The ability of defensins to oligomerize is being increasingly recognized as a critical feature underlying these activities 18 , 19 , 21 , 24 , 30 , 31 . The human defensins HD6 and HBD-1 have both been shown to oligomerize and form nets to trap bacteria 30 , 31 , however, the underlying molecular mechanism of action and any involvement of ligands remain to be clearly defined.…”

“…The human defensins HD6 and HBD-1 have both been shown to oligomerize and form nets to trap bacteria 30 , 31 , however, the underlying molecular mechanism of action and any involvement of ligands remain to be clearly defined. In plants, the ability of certain defensins to attack and permeabilize target membranes has been shown to be dependent on the recognition of specific membrane phospholipids such as PIP 2 or PA, and subsequent formation of oligomeric defensin–phospholipid complexes 18 , 19 , 21 . Binding of PIP 2 by the plant defensins NaD1 and TPP3 results in defensin oligomerization, membrane permeabilization, and killing of tumor cells as well as fungi 18 , 20 .…”

“…The mechanisms of action underlying membrane disruption by CAPs, including defensins, have not been fully defined and several putative modes of membrane attack have been proposed, including the (i) carpet, (ii) barrel-stave and (iii) toroidal-pore models 3 , 17 . Recently we demonstrated that the ability of certain plant defensins to kill fungal and tumor cells is dependent on the engagement of specific membrane phospholipids, which trigger the formation of large defensin–phospholipid oligomers 18 – 21 . Intriguingly, the phospholipid binding sites as well as the molecular architecture of the resultant oligomeric complexes that mediate membrane permeabilization are strikingly different.…”

A novel bi-domain plant defensin MtDef5 with potent broad-spectrum antifungal activity binds to multiple phospholipids and forms oligomers

“…NaD1 and TPP3 have been reported to oligomerize in presence of PIP 2 13 , 15 , whereas NsD7 has been reported to oligomerize in presence of PA 16 . Recently, both NaD1 and NsD7 have also been reported to oligomerize in presence of PA and PIP 2 33 . Our findings raise important questions regarding the mechanism of phospholipid-dependent oligomerization of MtDef5.…”