Source - http://cegg.unige.ch/Insecta/immunodb

BGBPs: 1,3-beta-D Glucan Binding Proteins
Summary

Lihui Wang and Petros Ligoxygakis 

Department of Biochemistry, University of Oxford, South Parks Road, Oxford, UK 

The GNBP/Beta-1,3-Glucan recognition family of proteins comprises members from several insects [Zhang et al. 2003]. These proteins contain an N-terminal glucan binding domain and a C-terminal domain similar to Beta-1,3- and Beta-1,4- bacterial glucanases [Yahata et al. 1990]. The Dm genome contains three unique GNBPs, sharing a 36% sequence homology between each other. GNBP1 has been proved both genetically and biochemically to be the co-receptor for Gram-positive bacteria along with PGRP-SA [Gobert et al. 2003; Wang et al. 2006]. Both the genomes of Ag and Aa have 7 GNBPs. These GNBPs can be classified into two subgroups: GNBPA and GNBPB. GNBPA1 and GNBPA2 are gene duplications with a higher homology to Dm GNBP1. Annotated sequences of mosquito GNBPBs however, indicate that this is a distinct sub-family of GNBPs unique to mosquitoes. Interestingly, the mosquito GNBPs show considerable conservation both between each other and with bacterial glucanases over the glucanase-like domain. This may point to the significance of a hydrolytic function of GNBPs to Gram-positive bacteria cell wall components in invertebrate innate immunity. In Ag, GNBPB1 has been linked with resistance to P. berghei and E. coli infection, while it lacked activity against P. falciparum and S. aureus [Dong et al. 2006]. Our studies indicate a similar function for GNBP1 in the fly [Wang et al. 2006]. The N-terminal part of all GNBPs is much less conserved and shows a significant variation even within species. The exact function of this domain still remains unknown. In DmGNBP1, this region is speculated to have similar glucan binding activity as in its bacterial counterparts. Therefore, a variation of this region might constitute a diversity of the GNBPs in pathogen recognition. Indeed, from the microarray data, different Ag GNBPs responded to S. aureus infection with a significant up or down regulation compared to E.coli and B. bassiana challenge, indicating that Ag GNBPs might be also involved in the Gram-positive bacterial defense as in Dm. Aa GNBPs seemed to respond equally well to all three infections, making the roles of Aa GNBPs more illusive in its immune defense. 

Warr et al, 2008, Insect Mol Biol. PMID:18237283 
The Gram-negative bacteria-binding protein gene family: its role in the innate immune system of Anopheles gambiae and in anti-Plasmodium defence.