Title
Domain-Swapped Dimers of Intracellular Lipid-Binding Proteins: Evidence for Ordered Folding Intermediates
Author
Zahra Assar, Zahra Nossoni, Wenjing Wang, Elizabeth M. Santos, Kevin Kramer, Colin McCornack, Chrysoula Vasileiou, Babak Borhan, James H. Geiger
Year
2016
Journal
Structure
Abstract
Human Cellular Retinol Binding Protein II (hCRBPII), a member of the intracellular lipid-binding protein family, is a monomeric protein responsible for the intracellular transport of retinol and retinal. Herein we report that hCRBPII forms an extensive domain-swapped dimer during bacterial expression. The domain-swapped region encompasses almost half of the protein. The dimer represents a novel structural architecture with the mouths of the two binding cavities facing each other, producing a new binding cavity that spans the length of the protein complex. Although wild-type hCRBPII forms the dimer, the propensity for dimerization can be substantially increased via mutation at Tyr60. The monomeric form of the wild-type protein represents the thermodynamically more stable species, making the domain-swapped dimer a kinetically trapped entity. Hypothetically, the wild-type protein has evolved to minimize dimerization of the folding intermediate through a critical hydrogen bond (Tyr60-Glu72) that disfavors the dimeric form.
Instrument
J-810
Keywords
Circular dichroism, Secondary structure, Thermal stability, Thermodynamics, Protein folding, Biochemistry