title: Reversible dimerization of acid-denatured ACBP controlled by helix A4.
abstract: The peptide segment corresponding to helix A4 in acyl-coenzyme-A-binding protein (ACBP) is an exceptionally stable helix in the denatured state of the protein as well as in its isolated form. Circular dichroism spectroscopy showed an alpha-helix content in the helix A4 peptide (HA4) of 45%, and under denaturing conditions at pH 2.3, helix conformations are still populated in 24% of the ensemble of molecules. The structure of HA4 at atomic resolution was assessed using nuclear magnetic resonance (NMR) spectroscopy. Long-range NOEs between remote residues at opposite peptide ends suggested the formation of an antiparallel homodimer, and the resulting structure was treated as the minimum higher-order structure. The dimerization property of helix A4 is maintained in the full-length protein under denaturing conditions. NMR diffusion studies and concentration-dependent experiments on ACBP at low pH proved the formation of dimers and revealed a cooperative stabilization of helix A4 in this process. This emphasizes its special role in the structure formation in the denatured state of ACBP. No dimers are formed in the presence of guanidine hydrochloride, which underlines the fundamental difference between the nature of these two denatured states.
authors.affiliation: Department of Protein Chemistry, Institute of Molecular Biology, University of Copenhagen, Øster Farimagsgade 2A, DK-1353 Copenhagen, Denmark.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Fieber
authors.forename: Birthe B
authors.initials: BB
authors.lastname: Kragelund
authors.forename: Morten
authors.initials: M
authors.lastname: Meldal
authors.forename: Flemming M
authors.initials: FM
authors.lastname: Poulsen
mesh_terms: D000143:Acids; D000818:Animals; D002417:Cattle; D002942:Circular Dichroism; D026261:Diazepam Binding Inhibitor / Q000737:chemistry*; D019281:Dimerization; D019791:Guanidine / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D009587:Nitrogen Isotopes; D019906:Nuclear Magnetic Resonance, Biomolecular; D011489:Protein Denaturation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence; D013329:Structure-Activity Relationship; D013816:Thermodynamics
chemical_list: D000143:Acids; D026261:Diazepam Binding Inhibitor; D009587:Nitrogen Isotopes; D019791:Guanidine