The knob protein KAHRP assembles into a ring-shaped structure that underpins virulence complex assembly.

The knob protein KAHRP assembles into a ring-shaped structure that underpins virulence complex assembly.

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Plasmodium falciparum mediates adhesion of infected red blood cells (RBCs) to blood vessel walls 100w products by assembling a multi-protein complex at the RBC surface.This virulence-mediating structure, called the knob, acts as a scaffold for the presentation of the major virulence antigen, P.falciparum Erythrocyte Membrane Protein-1 (PfEMP1).

In this work we developed correlative STochastic Optical Reconstruction Microscopy-Scanning Electron Microscopy (STORM-SEM) to spatially and temporally map the delivery of the knob-associated histidine-rich protein (KAHRP) and PfEMP1 to the RBC membrane skeleton.We show that KAHRP is delivered as individual modules that assemble in situ, giving a ring-shaped fluorescence profile around a dimpled disk 730 sunken lake road that can be visualized by SEM.Electron tomography of negatively-stained membranes reveals a previously observed spiral scaffold underpinning the assembled knobs.

Truncation of the C-terminal region of KAHRP leads to loss of the ring structures, disruption of the raised disks and aberrant formation of the spiral scaffold, pointing to a critical role for KAHRP in assembling the physical knob structure.We show that host cell actin remodeling plays an important role in assembly of the virulence complex, with cytochalasin D blocking knob assembly.Additionally, PfEMP1 appears to be delivered to the RBC membrane, then inserted laterally into knob structures.