Journal
JOURNAL OF MOLECULAR BIOLOGY
Volume 403, Issue 4, Pages 616-629Publisher
ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jmb.2010.09.022
Keywords
Toxoplasma gondii; profilin; Toll-like receptor 11; innate immune recognition; actin binding
Categories
Funding
- Burroughs Wellcome Investigator Award
- National Science Foundation [MCB-0546353]
- National Institutes of Health (NIH) [GM071688, AI033443, AI059440]
- American Heart Association [0940075N]
- Hellman Family
- NIH National Center for Research Resources [RR-15301]
- Offices of Biological and of Basic Energy Sciences of the U.S. Department of Energy [DE-AC02-06CH11357]
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Profilins promote actin polymerization by exchanging ADP for ATP on monomeric actin and delivering ATP-actin to growing filament barbed ends. Apicomplexan protozoa such as Toxoplasma gondii invade host cells using an actin-dependent gliding motility. Toll-like receptor (TLR) 11 generates an innate immune response upon sensing T. gondii profilin (TgPRF). The crystal structure of TgPRF reveals a parasite-specific surface motif consisting of an acidic loop, followed by a long beta-hairpin. A series of structure-based profilin mutants show that TLR11 recognition of the acidic loop is responsible for most of the interleukin (IL)-12 secretion response to TgPRF in peritoneal macrophages. Deletion of both the acidic loop and the beta-hairpin completely abrogates IL-12 secretion. Insertion of the T. gondii acidic loop and beta-hairpin into yeast profilin is sufficient to generate TLR11-dependent signaling. Substitution of the acidic loop in TgPRF with the homologous loop from the apicomplexan parasite Cryptosporidium parvum does not affect TLR11-dependent IL-12 secretion, while substitution with the acidic loop from Plasmodium falciparum results in reduced but significant IL-12 secretion. We conclude that the parasite-specific motif in TgPRF is the key molecular pattern recognized by TLR11. Unlike other profilins, TgPRF slows nucleotide exchange on monomeric rabbit actin and binds rabbit actin weakly. The putative TgPRF actin-binding surface includes the beta-hairpin and diverges widely from the actin-binding surfaces of vertebrate profilins. (C) 2010 Elsevier Ltd. All rights reserved.
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