Anopheles Fibrinogen-related Proteins Provide Expanded Pattern Recognition Capacity against Bacteria and Malaria Parasites

Yuemei Dong,George Dimopoulos

doi:10.1074/jbc.m807084200

Abstract

The fibrinogen-related protein family (FREP, also known as FBN) is an evolutionarily conserved immune gene family found in mammals and invertebrates. It is the largest pattern recognition receptor gene family in Anopheles gambiae, with as many as 59 putative members, while the Drosophila melanogaster genome has only 14 known FREP members. Our sequence and phylogenetic analysis suggest that this remarkable gene expansion in the mosquito is the result of tandem duplication of the fibrinogen domain. We found that the majority of the FREP genes displayed immune-responsive transcription after challenge with bacteria, fungi, or Plasmodium, and these expression patterns correlated strongly with gene phylogeny and chromosomal location. Using RNAi-mediated gene-silencing assays, we further demonstrated that some FREP members are essential factors of the mosquito innate immune system that are required for maintaining immune homeostasis, and members of this family have complementary and synergistic functions. One of the most potent anti-Plasmodium FREP proteins, FBN9, was found to interact with both Gram-negative and Gram-positive bacteria and strongly co-localized with both rodent and human malaria parasites in the mosquito midgut epithelium, suggesting that its defensive activity involves direct interaction with the pathogen. Interestingly, FBN9 formed dimers that bound to the bacterial surfaces with different affinities. Our findings indicate that the A. gambiae FREP gene family plays a central role in the mosquito innate immune system and provides an expanded pattern recognition and anti-microbial defense repertoire.

Highlights

Humoral mechanisms that are activated upon recognition of invading pathogens by the mosquito pattern recognition receptor (PRR) molecules
Through a comparison to the A. aegypti fibrinogen-related proteins (FREPs) phylogenetic tree, we found that some clusters were composed of FBG domains from A. gambiae alone and not from A. aegypti, suggesting that the FREP gene family evolved by expansions that occurred in A. gambiae after its divergence from other mosquito species [37]
Our phylogenetic and cytogenetic analyses of the FREP family members suggest that the expansion of this gene family is mainly accounted for by a major expansion of FBG domains, through both tandem duplications and shuffling mechanisms

Summary

Introduction

Humoral mechanisms that are activated upon recognition of invading pathogens by the mosquito pattern recognition receptor (PRR) molecules. Among the three distinct fibrinogen domain immunolectins that been identified, ficolins are the most important molecules in terms of their function as pattern recognition receptors in phagocytosis and complement activation (18 –25). All of these FREPs contain a pathogen-binding FBG domain at their C terminus, and their N-terminal sequence is likely involved in APRIL 10, 2009 VOLUME 284 NUMBER 15. A very recent interesting observation is that the FREPs demonstrated the recognition specificities to different categories of pathogens with FREP4 bound to parasites [36]

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Results

Conclusion