title: Domain-Swapped Dimers of Intracellular Lipid-Binding Proteins: Evidence for Ordered Folding Intermediates.
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.
authors.affiliation: Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: Zahra
authors.initials: Z
authors.lastname: Assar
authors.affiliation: Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: Zahra
authors.initials: Z
authors.lastname: Nossoni
authors.affiliation: Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: Wenjing
authors.initials: W
authors.lastname: Wang
authors.affiliation: Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Santos
authors.affiliation: Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: Kevin
authors.initials: K
authors.lastname: Kramer
authors.affiliation: Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: Colin
authors.initials: C
authors.lastname: McCornack
authors.affiliation: Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: Chrysoula
authors.initials: C
authors.lastname: Vasileiou
authors.affiliation: Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA. Electronic address: babak@chemistry.msu.edu.
authors.forename: Babak
authors.initials: B
authors.lastname: Borhan
authors.affiliation: Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA. Electronic address: geiger@chemistry.msu.edu.
authors.forename: James H
authors.initials: JH
authors.lastname: Geiger
mesh_terms: D020816:Amino Acid Motifs; D019943:Amino Acid Substitution; D001665:Binding Sites; D018360:Crystallography, X-Ray; D015870:Gene Expression; D018698:Glutamic Acid / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D006860:Hydrogen Bonding; D007700:Kinetics; D008958:Models, Molecular; D009154:Mutation; D011485:Protein Binding; D000072756:Protein Conformation, alpha-Helical; D000072757:Protein Conformation, beta-Strand; D000072417:Protein Domains; D017510:Protein Folding; D055503:Protein Multimerization; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D054840:Retinol-Binding Proteins, Cellular / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013816:Thermodynamics; D014443:Tyrosine / Q000737:chemistry* / Q000378:metabolism
chemical_list: C518459:RBP2 protein, human; D011994:Recombinant Proteins; D054840:Retinol-Binding Proteins, Cellular; D018698:Glutamic Acid; D014443:Tyrosine