Abstract
Brugia malayi is a causative agent of lymphatic filariasis, a major tropical disease. The infective L3 parasite stage releases immunomodulatory proteins including the venom allergen-like proteins (VALs), which are members of the SCP/TAPS (Sperm-coating protein/Tpx/antigen 5/pathogenesis related-1/Sc7) superfamily. BmVAL-1 is a major target of host immunity with >90% of infected B. malayi microfilaraemic cases being seropositive for antibodies to BmVAL-1. This study is part of ongoing efforts to characterize the structures and functions of important B. malayi proteins. Recombinant BmVAL-1 was produced using a plant expression system, crystallized and the structure was solved by molecular replacement and refined to 2.1 Å, revealing the characteristic alpha/beta/alpha sandwich topology of eukaryotic SCP/TAPS proteins. The protein has more than 45% loop regions and these flexible loops connect the helices and strands, which are longer than predicted based on other parasite SCP/TAPS protein structures. The large central cavity of BmVAL-1 is a prototypical CRISP cavity with two histidines required to bind divalent cations. The caveolin-binding motif (CBM) that mediates sterol binding in SCP/TAPS proteins is large and open in BmVAL-1 and is N-glycosylated. N-glycosylation of the CBM does not affect the ability of BmVAL-1 to bind sterol in vitro. BmVAL-1 complements the in vivo sterol export phenotype of yeast mutants lacking their endogenous SCP/TAPS proteins. The in vitro sterol-binding affinity of BmVAL-1 is comparable with Pry1, a yeast sterol transporting SCP/TAPS protein. Sterol binding of BmVAL-1 is dependent on divalent cations. BmVAL-1 also has a large open palmitate-binding cavity, which binds palmitate comparably to tablysin-15, a lipid-binding SCP/TAPS protein. The central cavity, CBM and palmitate-binding cavity of BmVAL-1 are interconnected within the monomer with channels that can serve as pathways for water molecules, cations and small molecules.
Highlights
The roundworm Brugia malayi is one of the causative agents of lymphatic filariasis that affects over 120 million people in 83 countries in the tropics and subtropics
The glycosylation site at N138 is within the caveolin-binding motif (CBM) loop that is required for sterol export (Fig. 1A)
Brugia malayi venom allergenlike protein 1 (BmVAL-1) is the first structure of a SCP/TAPS protein with a glycosylated CBM loop that exports sterols, which indicates that glycosylation of the CBM does not inhibit sterol binding
Summary
The roundworm Brugia malayi is one of the causative agents of lymphatic filariasis that affects over 120 million people in 83 countries in the tropics and subtropics. Brugia malayi venom allergenlike protein 1 (BmVAL-1) protein was discovered as a highly expressed transcript representing 2% of cDNAs from the mosquito-borne infective larval (L3) stage, and at lower levels in subsequent post-infective mammalian stages (Murray et al, 2001). BmVAL-1 is a major target of host immunity with >90% of infected B. malayi microfilaraemic cases being seropositive for the recombinant protein, and evidence from mouse models that the antigen induces a strong T cell response (Murray et al, 2001). T cells from humans infected with the closely related species Wuchereria bancrofti respond to the Wb-VAL (>90% identical at amino acid level) with proliferation and cytokine release (Anand et al, 2007). BmVAL-1 has been considered a potential vaccine antigen, with confirmed serological reactivity in infected humans and a reported 40–50% reduction in adult worm load in jirds (Meriones unguiculatus) that had been vaccinated with BmVAL-1 prior to L3 challenge (Kalyanasundaram and Balumuri, 2011)
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call