title: The polyprotein and FAR lipid binding proteins of nematodes: shape and monomer/dimer states in ligand-free and bound forms.
abstract: Nematodes produce two classes of small, helix-rich fatty acid- and retinol-binding proteins whose structures and in vivo functions remain to be elucidated. These are the polyprotein allergens (NPA) and the FAR proteins. The solution properties of recombinant forms of these proteins from parasitic [Ascaris suum (As) and Onchocerca volvulus (Ov)] and free-living [Caenorhabditis elegans (Ce)] nematodes have been examined. Analytical ultracentrifugation (AUC) showed that, contrary to previous findings, the rAs-NPA-1A polyprotein unit (approximately 15 kDa) is a monomer, and this stoichiometry is unaltered by ligand (oleic acid) binding. The rOv-FAR-1 and rCe-FAR-5 proteins differ in that the former forms a tight dimer and the latter a monomer, and these oligomeric states are also unaffected by ligand binding or protein concentration. Sedimentation equilibrium experiments showed that the partial specific volume v of the unliganded proteins agree well with the value calculated from amino acid composition extrapolated to experimental temperature, and was unaffected upon ligand binding. Data from small-angle X-ray scattering (SAXS) indicated that both of the monomeric proteins rAs-NPA-1A and rCe-FAR-5 are globular, although slightly elongated and flattened. These data are in good agreement with shapes predicted from sedimentation velocity experiments and hydrodynamic bead modelling. On the basis of functional and secondary structural homology with the ligand-binding domain of the retinoic acid receptor RXRalpha, de novo atomic resolution structures for rAs-NPA-1A and rCe-FAR-5 have been constructed which are consistent with the SAXS and hydrodynamic data.
authors.affiliation: Division of Infection and Immunity, Institute of Biomedical and Life Sciences, Joseph Black Building, University of Glasgow, Glasgow, G12 8QQ, UK. alexandra.solovyova@bio.gla.ac.uk
authors.forename: Alexandra S
authors.initials: AS
authors.lastname: Solovyova
authors.forename: Nicola
authors.initials: N
authors.lastname: Meenan
authors.forename: Lindsay
authors.initials: L
authors.lastname: McDermott
authors.forename: Antonio
authors.initials: A
authors.lastname: Garofalo
authors.forename: Jannette E
authors.initials: JE
authors.lastname: Bradley
authors.forename: Malcolm W
authors.initials: MW
authors.lastname: Kennedy
authors.forename: Olwyn
authors.initials: O
authors.lastname: Byron
mesh_terms: D000485:Allergens / Q000032:analysis / Q000737:chemistry; D000595:Amino Acid Sequence; D000818:Animals; D001200:Ascaris; D001665:Binding Sites; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins / Q000032:analysis* / Q000737:chemistry* / Q000235:genetics; D002352:Carrier Proteins / Q000032:analysis* / Q000737:chemistry* / Q000235:genetics; D002499:Centrifugation, Density Gradient / Q000379:methods*; D003198:Computer Simulation; D019281:Dimerization; D008024:Ligands; D008055:Lipids / Q000737:chemistry; D046911:Macromolecular Substances; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009854:Onchocerca; D010316:Particle Size; D020815:Polyproteins / Q000032:analysis* / Q000737:chemistry*; D011485:Protein Binding; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000032:analysis / Q000737:chemistry; D020539:Sequence Analysis, Protein / Q000379:methods*; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship; D014961:X-Ray Diffraction
chemical_list: D000485:Allergens; D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; C473216:FAR protein, C elegans; D008024:Ligands; D008055:Lipids; D046911:Macromolecular Substances; D020815:Polyproteins; D011994:Recombinant Proteins