A residual structure in unfolded intestinal fatty acid binding protein consists of amino acids that are neighbors in the native state.
Much of the recent effort in protein folding has focused on the possibility that residual structures in the unfolded state may provide an initiating site for protein folding. This hypothesis is difficult to test because of the weak stability and dynamic behavior of these structures. This problem has been simplified for intestinal fatty acid binding protein (IFABP) by incorporating fluorinated aromatic amino acids during synthesis in Escherichia coli. Only the labeled residues give signals by (19)F NMR, and the 1D spectra can be assigned in both the native and unfolded states by site-directed mutagenesis. One of the two tryptophans (W82), one of the four tyrosines (Y70), and at least four of the eight phenylalanines (including F68 and F93) of IFABP are involved in a structure that is significantly populated at concentrations of urea that unfold the native structure by fluorescence and CD criteria. These residues are nonlocal in sequence and also contact each other in the native structure. Thus, a template of nativelike hydrophobic contacts in the unfolded state may serve as an initiating site for folding this beta-sheet protein.
Department of Biochemistry and Molecular Biology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA. iropson@psu.edu
Ira J
IJ
Ropson
Joshua A
JA
Boyer
Paula M
PM
Dalessio
D000596:Amino Acids / Q000737:chemistry*; D002942:Circular Dichroism; D050556:Fatty Acid-Binding Proteins / Q000737:chemistry* / Q000235:genetics; D005453:Fluorescence; D005461:Fluorine / Q000737:chemistry / Q000378:metabolism; D057927:Hydrophobic and Hydrophilic Interactions; D019906:Nuclear Magnetic Resonance, Biomolecular; D010649:Phenylalanine / Q000737:chemistry; D011489:Protein Denaturation; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000378:metabolism; D014364:Tryptophan / Q000737:chemistry / Q000235:genetics; D014443:Tyrosine / Q000737:chemistry; D014508:Urea / Q000378:metabolism
D000596:Amino Acids; D050556:Fatty Acid-Binding Proteins; D011994:Recombinant Proteins; D005461:Fluorine; D014443:Tyrosine; D010649:Phenylalanine; D014364:Tryptophan; D014508:Urea