title: Slowly interchanging conformers of bovine neurophysin-I in the unliganded dimeric state.
abstract: The effect of neurophysin dimerization on Tyr-49, a residue adjacent to the hormone-binding site, was investigated by proton NMR in order to analyze the basis of the dimerization-induced increase in neurophysin hormone affinity. Dimerization-induced changes in Tyr-49 resonances, in two unliganded bovine neurophysins, suggested that Tyr-49 perturbation is an intrinsic consequence of dimerization, although Tyr-49 is distant from the monomer-monomer interface in the crystalline liganded state. To determine whether this perturbation reflects a conformational difference between liganded and unliganded states that places Tyr-49 at the interface in the unliganded state, or a dimerization-induced change in secondary (2 degrees) or tertiary (3 degrees) structure, the more general structural consequences of dimerization were further analyzed. No change in 2 degrees structure upon dimerization was demonstrable by CD. On the other hand, a general similarity of regions involved in dimerization in unliganded and liganded states was indicated by NMR evidence of participation of His-80 and Phe-35 in dimerization in the unliganded state; both residues are at the interface in the crystal structure and distant from Tyr-49. Consistent with a lack of direct participation of Tyr-49 at the monomer-monomer interface, dimerization induced at least two distinct slowly exchanging environmental states for the 3.5 ring protons of Tyr-49 without significantly increased dipolar broadening relative to the monomer. Two environments were also found in the dimer of des-1-8 neurophysin-I for the methyl protons of Thr-9, another residue distant from the monomer-monomer interface and close to the binding site in the liganded state.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Biochemistry, Cornell University Medical College, New York, New York 10021.
authors.forename: E
authors.initials: E
authors.lastname: Breslow
authors.forename: P K
authors.initials: PK
authors.lastname: Mishra
authors.forename: H B
authors.initials: HB
authors.lastname: Huang
authors.forename: A
authors.initials: A
authors.lastname: Bothner-by
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D002942:Circular Dichroism; D006863:Hydrogen-Ion Concentration; D007536:Isomerism; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D009481:Neurophysins / Q000737:chemistry*; D011487:Protein Conformation; D013056:Spectrophotometry, Ultraviolet
chemical_list: D009481:Neurophysins