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Beta-sheet proteins with nearly identical structures have different folding intermediates
1Department of Biochemistry and Molecular Biology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
Biochemistry
|February 2, 2000
Summary
The folding mechanisms of ileal lipid binding protein (ILBP) and intestinal fatty acid binding protein (IFABP) differ significantly, despite their similar structures. These proteins utilize distinct folding pathways to reach their final forms, influenced by their unique amino acid sequences.
Area of Science:
- Biochemistry
- Structural Biology
- Protein Folding Dynamics
Background:
- Intracellular lipid binding proteins (ILBPs) share structural similarities but exhibit sequence divergence.
- Understanding protein folding mechanisms is crucial for comprehending protein function and dysfunction.
Purpose of the Study:
- To investigate and compare the folding mechanisms of ileal lipid binding protein (ILBP) and intestinal fatty acid binding protein (IFABP).
- To elucidate how sequence differences influence folding pathways despite structural homology.
Main Methods:
- Circular dichroism (CD) and fluorescence spectroscopy were used to monitor protein folding.
- Stopped-flow kinetic studies and double-jump experiments were employed to analyze folding and unfolding kinetics and intermediate states.
Main Results:
- Both ILBP and IFABP folding processes were reversible and multiphasic, indicating complex pathways or intermediates.
- ILBP exhibited a molten globule-like intermediate, while IFABP showed an intermediate with minimal secondary structure.
- ILBP was found to be less stable than IFABP, with different urea denaturation midpoints.
Conclusions:
- Despite high structural similarity, ILBP and IFABP fold via markedly different mechanisms.
- Divergent amino acid sequences dictate distinct folding pathways through the energy landscape to achieve the same final structure.