Source: ImmunoDB
http://cegg.unige.ch/insecta/immunodb/

FREPs: Fibrinogen-Related Proteins
Summary

Yuemei Dong and George Dimopoulos 

Department of Molecular Microbiology and Immunology, Malaria Research Institute, Bloomberg School of Public Health, Johns Hopkins University, 615 N. Wolfe street, Baltimore, MD 21205-2179, USA 

Members of the fibrinogen-related proteins (FREPs) or fibrinogen-domain immuno-lectin (FBN) family contain the evolutionary conserved fibrinogen domain that is also found in the mammalian ficolins [Adema et al. 1997; Gokudan et al. 1999; Dimopoulos et al. 2000; Kairies et al. 2001; Dimopoulos et al. 2002; Zdobnov et al. 2002; Wang et al. 2005]. The ficolins are implicated in phagocytosis and complement activation, while the horseshoe crab and snail FBN genes have been implicated in bacteria binding, enhancement of antimicrobial activity and interaction with parasite (Schistosoma) components, respectively. The FREPs contain a pathogen-binding fibrinogen-like domain at their C-terminus and the N-terminal sequence is implicated in interactions with the N-terminus of other FBN proteins resulting in the formation of multimeric protein bundles with potentially increased affinity and specificity to the pathogens. FREPs exhibit species-specific expansions with only two identifiable 1:1:1 orthologous trios and three 1:1 mosquito orthologous pairs. The most notable expansion is found in Ag, which harbors as many as 61 members, compared to Aa with 37 and Dm with only 14 FREPs. However, due to the lack of confidence in the quality of certain Aa FREP pseudogene sequences, the gene family in this species might turn out to be somewhat larger that currently predicted. The reason for this remarkable expansion in the mosquitoes remains unknown, but it has been speculated to be partly linked to hematophagy. Several Ag FREPs have been shown to be up-regulated by bacterial challenge and malarial infection [Christophides et al. 2002; Dimopoulos et al. 2002; Dong et al. 2006] (Dimopoulos, unpublished data). The ability of FREPs to form multimers (dimers in Ag cell line supernatant) may enable an increase of the mosquito�s pattern recognition receptor repertoire since different combinations are likely to posses different binding specificities (Dong & Dimopoulos, unpublished data). The phylogenetic tree was built from the alignment of FREP sequences to the Pfam HMM profile of the Fibrinogen domain (PF00147). Several proteins were removed (3 from Aa, 9 from Ag) as they were lacking sequences mostly at the N or C-terminal which may be a result of gene predictions missing the first and/or last exons.