title: The Ov20 protein of the parasitic nematode Onchocerca volvulus. A structurally novel class of small helix-rich retinol-binding proteins.
abstract: Ov20 is a major antigen of the parasitic nematode Onchocerca volvulus, the causative agent of river blindness in humans, and the protein is secreted into the tissue occupied by the parasite. DNA encoding Ov20 was isolated, and the protein was expressed in Escherichia coli. Fluorescence-based ligand binding assays show that the protein contains a high affinity binding site for retinol, fluorescent fatty acids (11-((5-dimethylaminonaphthalene-1-sulfonyl)amino)undecanoic acid, dansyl-DL-alpha-aminocaprylic acid, and parinaric acid) and, by competition, oleic and arachidonic acids, but not cholesterol. The fluorescence emission of dansylated fatty acids is significantly blue-shifted upon binding in comparison to similarly sized beta-sheet-rich mammalian retinol- and fatty acid-binding proteins. Secondary structure prediction algorithms indicate that a alpha-helix predominates in Ov20, possibly in a coiled coil motif, with no evidence of beta structures, and this was confirmed by circular dichroism. The protein is highly stable in solution, requiring temperatures in excess of 90 degrees C or high denaturant concentrations for unfolding. Ov20 therefore represents a novel class of small retinol-binding protein, which appears to be confined to nematodes. The retinol binding activity of Ov20 could possibly contribute to the eye defects associated with onchocerciasis and, because there is no counterpart in mammals, represents a strategic target for chemotherapy.
authors.affiliation: Division of Infection and Immunity, Institute of Biomedical and Life Sciences, Joseph Black Building, University of Glasgow, Glasgow G12 8QQ, United Kingdom. malcolm.kennedy@bio.gla.ac.uk
authors.forename: M W
authors.initials: MW
authors.lastname: Kennedy
authors.forename: L H
authors.initials: LH
authors.lastname: Garside
authors.forename: L E
authors.initials: LE
authors.lastname: Goodrick
authors.forename: L
authors.initials: L
authors.lastname: McDermott
authors.forename: A
authors.initials: A
authors.lastname: Brass
authors.forename: N C
authors.initials: NC
authors.lastname: Price
authors.forename: S M
authors.initials: SM
authors.lastname: Kelly
authors.forename: A
authors.initials: A
authors.lastname: Cooper
authors.forename: J E
authors.initials: JE
authors.lastname: Bradley
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000947:Antigens, Helminth / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001667:Binding, Competitive; D002942:Circular Dichroism; D003619:Dansyl Compounds / Q000378:metabolism; D005227:Fatty Acids / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D008969:Molecular Sequence Data; D019301:Oleic Acid / Q000378:metabolism; D017181:Onchocerca volvulus / Q000737:chemistry*; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000378:metabolism; D012177:Retinol-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D013050:Spectrometry, Fluorescence; D014801:Vitamin A / Q000378:metabolism
chemical_list: D000947:Antigens, Helminth; D003619:Dansyl Compounds; D005227:Fatty Acids; D005456:Fluorescent Dyes; C109308:Ov20 antigen; D011994:Recombinant Proteins; D012177:Retinol-Binding Proteins; D014801:Vitamin A; D019301:Oleic Acid; C054400:11-(dansylamino)undecanoic acid