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Asojo OA, Darwiche R, Gebremedhin S, Smant G, Lozano-Torres JL, Drurey C, Pollet J, Maizels RM, Schneiter R, Wilbers RHP. Heligmosomoides polygyrus Venom Allergen-like Protein-4 (HpVAL-4) is a sterol binding protein. Int J Parasitol 2018; 48:359-369. [PMID: 29505764 PMCID: PMC5893428 DOI: 10.1016/j.ijpara.2018.01.002] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2017] [Revised: 12/07/2017] [Accepted: 01/02/2018] [Indexed: 12/13/2022]
Abstract
Heligmosomoides polygyrus Venom Allergen-like Protein-4 (HpVAL-4) was produced in plants as a glycosylated protein. The crystal structure of HpVAL-4 was solved and reveals three distinct cavities. These cavities are the central cavity; the sterol-binding caveolin-binding motif (CBM); and the palmitate-binding cavity. The central cavity of Hp-VAL-4 lacks the characteristic histidines that coordinate divalent cations. Hp-VAL-4 binds sterol in vivo and in vitro.
Heligmosomoides polygyrus bakeri is a model parasitic hookworm used to study animal and human helminth diseases. During infection, the parasite releases excretory/secretory products that modulate the immune system of the host. The most abundant protein family in excretory/secretory products comprises the venom allergen-like proteins (VALs), which are members of the SCP/TAPS (sperm-coating protein/Tpx/antigen 5/pathogenesis related-1/Sc7) superfamily. There are >30 secreted Heligmosomoides polygyrus VAL proteins (HpVALs) and these proteins are characterised by having either one or two 15 kDa CAP (cysteine-rich secretory protein (CRISP)/antigen 5/pathogenesis related-1) domains. The first known HpVAL structure, HpVAL-4, refined to 1.9 Å is reported. HpVAL-4 was produced as a homogeneously glycosylated protein in leaves of Nicotiana benthamiana infiltrated with recombinant plasmids, making this plant expression platform amenable for the production of biological products. The overall topology of HpVAL-4 is a three layered αβα sandwich between a short N-terminal loop and a C-terminal cysteine rich extension. The C-terminal cysteine rich extension has two strands stabilized by two disulfide bonds and superposes well with the previously reported extension from the human hookworm Necator americanus Ancylostoma secreted protein-2 (Na-ASP-2). The N-terminal loop is connected to alpha helix 2 via a disulfide bond previously observed in Na-ASP-2. HpVAL-4 has a central cavity that is more similar to the N-terminal CAP domain of the two CAP Na-ASP-1 from Necator americanus. Unlike Na-ASP-2, mammalian CRISP, and the C-terminal CAP domain of Na-ASP-1, the large central cavity of HpVAL-4 lacks the two histidines required to coordinate divalent cations. HpVAL-4 has both palmitate-binding and sterol-binding cavities and is able to complement the in vivo sterol export phenotype of yeast mutants lacking their endogenous CAP proteins. More studies are required to determine endogenous binding partners of HpVAL-4 and unravel the possible impact of sterol binding on immune-modulatory functions.
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Affiliation(s)
- Oluwatoyin A Asojo
- National School of Tropical Medicine, Baylor College of Medicine, Houston, TX 77030, USA.
| | - Rabih Darwiche
- Division of Biochemistry, Department of Biology, University of Fribourg, Chemin du Musée 10, CH 1700 Fribourg, Switzerland
| | - Selam Gebremedhin
- National School of Tropical Medicine, Baylor College of Medicine, Houston, TX 77030, USA
| | - Geert Smant
- Laboratory of Nematology, Wageningen University, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands
| | - Jose L Lozano-Torres
- Laboratory of Nematology, Wageningen University, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands
| | - Claire Drurey
- Wellcome Centre for Molecular Parasitology, Institute for Infection, Immunity and Inflammation, University of Glasgow, Sir Graeme Davies Building, 120 University Place, Glasgow G12 8TA, UK
| | - Jeroen Pollet
- National School of Tropical Medicine, Baylor College of Medicine, Houston, TX 77030, USA
| | - Rick M Maizels
- Wellcome Centre for Molecular Parasitology, Institute for Infection, Immunity and Inflammation, University of Glasgow, Sir Graeme Davies Building, 120 University Place, Glasgow G12 8TA, UK
| | - Roger Schneiter
- Division of Biochemistry, Department of Biology, University of Fribourg, Chemin du Musée 10, CH 1700 Fribourg, Switzerland
| | - Ruud H P Wilbers
- Laboratory of Nematology, Wageningen University, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands
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