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

PLoS Pathog. 2019 May 9;15(5):e1007761. doi: 10.1371/journal.ppat.1007761. eCollection 2019 May.


Plasmodium falciparum mediates adhesion of infected red blood cells (RBCs) to blood vessel walls 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 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Erythrocyte Membrane / metabolism
  • Erythrocyte Membrane / parasitology*
  • Erythrocytes / metabolism
  • Erythrocytes / parasitology*
  • Humans
  • Malaria, Falciparum / metabolism
  • Malaria, Falciparum / parasitology*
  • Microscopy, Electron, Scanning
  • Peptides / chemistry
  • Peptides / metabolism*
  • Plasmodium falciparum / pathogenicity*
  • Protozoan Proteins / chemistry
  • Protozoan Proteins / metabolism*
  • Virulence


  • Peptides
  • Protozoan Proteins
  • erythrocyte membrane protein 1, Plasmodium falciparum
  • knob protein, Plasmodium falciparum

Grants and funding

LT is a Georgina Sweet, Australian Research Council Laureate Fellow (LE150100011) ( MWAD and LT thank the Australian Research Council (DP110100624) ( and the National Health and Medical Research Council (1098992) ( for funding this work. MWAD was supported by a National Health and Medical Research Council Training fellowship (602541). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.