013 NETs generate structured antimicrobial peptide-nucleosome immune complexes with inter-DNA spacings optimal for TLR9 activation

      The molecular pathogenesis of psoriasis is characterized in part by breakdown of immune tolerance to self-DNA. Recent work demonstrates that the human antimicrobial peptide (AMP) LL37 overexpressed in psoriasis organizes naked DNA into periodic nanocrystals to potently hyperactivate Toll-like receptor 9 (TLR9) in plasmacytoid dendritic cells (pDCs). Interestingly, a subset of self-DNA in psoriatic lesions remain bound to histones as histone-DNA nucleosome core particles (NCPs) released from neutrophil extracellular traps (NETs). At present, it is unknown how NET components like AMPs interact with NCPs, and whether AMP-NCP complexes form structures compatible with TLR9 activation in psoriasis. Here, we combine synchrotron X-ray scattering, cryo-electron microscopy, and computer simulations to demonstrate that under a broad range of conditions, NCPs stack into columns that present periodically arranged dsDNA ligands like threads on a screw, allowing for optimal interdigitation with clusters of TLR9. Remarkably, simulations and electron microscopy indicate that the superhelical pitch of DNA wrapped around the NCP column relaxes to a value that is well-matched with the steric size of TLR9, which predicts strong immune activation. Taken together, our results suggest that AMPs can remodel the structural organization of nucleosomes from NETs into potent amplifiers of inflammation. Preliminary immune activation experiments will be presented.