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Cell Rep. 2016 Feb 2;14(4):723-736. doi: 10.1016/j.celrep.2015.12.067. Epub 2016 Jan 14.

Architecture of Human IgM in Complex with P. falciparum Erythrocyte Membrane Protein 1.

Author information

1
Center for Infectious Disease Research (CID), Department of Microbiology, Tumor and Cell Biology (MTC), Karolinska Institutet, Nobels väg 16, Box 280, 171 77 Stockholm, Sweden.
2
Structural Cellular Biology Unit, Okinawa Institute for Science and Technology Graduate University, 1919-1 Tancha, Onna-son, Okinawa 904-0495, Japan.
3
Structural Cellular Biology Unit, Okinawa Institute for Science and Technology Graduate University, 1919-1 Tancha, Onna-son, Okinawa 904-0495, Japan. Electronic address: ulf.skoglund@oist.jp.
4
Center for Infectious Disease Research (CID), Department of Microbiology, Tumor and Cell Biology (MTC), Karolinska Institutet, Nobels väg 16, Box 280, 171 77 Stockholm, Sweden. Electronic address: mats.wahlgren@ki.se.

Abstract

Plasmodium falciparum virulence is associated with sequestration of infected erythrocytes. Microvascular binding mediated by PfEMP1 in complex with non-immune immunoglobulin M (IgM) is common among parasites that cause both severe childhood malaria and pregnancy-associated malaria. Here, we present cryo-molecular electron tomography structures of human IgM, PfEMP1 and their complex. Three-dimensional reconstructions of IgM reveal that it has a dome-like core, randomly oriented Fab2s units, and the overall shape of a turtle. PfEMP1 is a C- shaped molecule with a flexible N terminus followed by an arc-shaped backbone and a bulky C terminus that interacts with IgM. Our data demonstrate that the PfEMP1 binding pockets on IgM overlap with those of C1q, and the bulkiness of PfEMP1 limits the capacity of IgM to interact with PfEMP1. We suggest that P. falciparum exploits IgM to cluster PfEMP1 into an organized matrix to augment its affinity to host cell receptors.

PMID:
26776517
DOI:
10.1016/j.celrep.2015.12.067
[Indexed for MEDLINE]
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