title: Crystallization, structure determination and least-squares refinement to 1.75 A resolution of the fatty-acid-binding protein isolated from Manduca sexta L.
abstract: The molecular structure of an insect fatty-acid-binding protein isolated from Manduca sexta L. has been determined and refined to a nominal resolution of 1.75 A. Crystals used in the investigation were grown from 1.6 M-ammonium sulfate solutions buffered at pH 4.5 with 50 mM-sodium succinate, and belonged to space group P2(1) with unit cell dimensions of a = 27.5 A, b = 71.0 A, c = 28.7 A and beta = 90.8 degrees. An electron density map, phased with four heavy-atom derivatives and calculated to 2.5 A resolution, allowed for complete tracing of the 131 amino acid residue polypeptide chain. Subsequent least-squares refinement of the model reduced the R-factor from 46.0% to 17.3% using all measured X-ray data from 30.0 A to 1.75 A. Approximately 92% of the amino acid residues fall into classical secondary structural elements including ten strands of anti-parallel beta-pleated sheet, two alpha-helices, one type I turn, three type II turns, four type II' turns and one type III turn. As in other fatty-acid-binding proteins, the overall molecular architecture of the insect molecule consists of ten strands of anti-parallel beta-pleated sheet forming two layers that are nearly orthogonal to one another. A helix-turn-helix motif at the N-terminal portion of the protein flanks one side of the up-and-down beta-barrel. The functional group of the fatty acid is within hydrogen-bonding distance of Gln39, Tyr129, Arg127 and a sulfate molecule, while the aliphatic portion of the ligand is surrounded by hydrophobic amino acid residues lining the beta-barrel. The binding of the carboxylic acid portion of the ligand is very similar to that observed in P2 myelin protein and the murine adipocyte lipid-binding protein, but the positioning of the hydrocarbon tail after approximately C6 is completely different.
authors.affiliation: Institute for Enzyme Research, Graduate School, University of Wisconsin, Madison 53705.
authors.forename: M M
authors.initials: MM
authors.lastname: Benning
authors.forename: A F
authors.initials: AF
authors.lastname: Smith
authors.forename: M A
authors.initials: MA
authors.lastname: Wells
authors.forename: H M
authors.initials: HM
authors.lastname: Holden
mesh_terms: D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry*; D003460:Crystallization; D050556:Fatty Acid-Binding Proteins; D006860:Hydrogen Bonding; D008958:Models, Molecular; D009036:Moths / Q000737:chemistry*; D009363:Neoplasm Proteins; D017433:Protein Structure, Secondary; D014961:X-Ray Diffraction
chemical_list: D002352:Carrier Proteins; D050556:Fatty Acid-Binding Proteins; D009363:Neoplasm Proteins