Folding mechanism of three structurally similar beta-sheet proteins.
The folding mechanism of cellular retinoic acid binding protein I (CRABP I), cellular retinol binding protein II (CRBP II), and intestinal fatty acid binding protein (IFABP) were investigated to determine if proteins with similar native structures have similar folding mechanisms. These mostly beta-sheet proteins have very similar structures, despite having as little as 33% sequence similarity. The reversible urea denaturation of these proteins was characterized at equilibrium by circular dichroism and fluorescence. The data were best fit by a two-state model for each of these proteins, suggesting that no significant population of folding intermediates were present at equilibrium. The native states were of similar stability with free energies (linearly extrapolated to 0 M urea, deltaGH2O) of 6.5, 8.3, and 5.5 kcal/mole for CRABP I, CRBP II, and IFABP, respectively. The kinetics of the folding and unfolding processes for these proteins was monitored by stopped-flow CD and fluorescence. Intermediates were observed during both the folding and unfolding of all of these proteins. However, the overall rates of folding and unfolding differed by nearly three orders of magnitude. Further, the spectroscopic properties of the intermediate states were different for each protein, suggesting that different amounts of secondary and/or tertiary structure were associated with each intermediate state for each protein. These data show that the folding path for proteins in the same structural family can be quite different, and provide evidence for different folding landscapes for these sequences.
Burns
L L
LL
Department of Biochemistry and Molecular Biology, Pennsylvania State University, College of Medicine, Hershey 17033, USA.
Dalessio
P M
PM
Ropson
I J
IJ
D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry*; D002942:Circular Dichroism; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D007700:Kinetics; D051379:Mice; D008969:Molecular Sequence Data; D018996:Myelin P2 Protein / Q000737:chemistry*; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D011487:Protein Conformation; D017510:Protein Folding; D051381:Rats; D018168:Receptors, Retinoic Acid / Q000737:chemistry*; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid
D002352:Carrier Proteins; C082667:Fabp5 protein, mouse; C086936:Fabp7 protein, mouse; C490174:Fabp7 protein, rat; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D018996:Myelin P2 Protein; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D018168:Receptors, Retinoic Acid; D011993:Recombinant Fusion Proteins; C082927:retinoic acid binding protein I, cellular; C082928:retinoic acid binding protein II, cellular