Synthesis of peptide spin-labels that bind to neurophysin and their application to distance measurements within neurophysin complexes

Neurophysin-neurohypophyseal hormone interactions: studies using a dansylated vasotocin analogue

We have synthesized a neurohypophyseal hormone analogue containing an extrinsic fluorescence probe by linking a dansyl (DNS) group to the epsilon-amino group of the lysine at residue 8 of vasotocin. The fluorescence properties of this analogue have been characterized by steady-state and time-resolved spectroscopic methods and compared with those of epsilon-DNS-lysine and the dansylated carboxyl terminal tripeptide Pro-Lys(DNS)-GlyNH2. The binding of this hormone analogue to purified isoforms of bovine neurophysins, the natural carrier proteins of the neurohypophyseal hormones, results in changes in several fluorescence parameters of the dansyl probe. These changes include an increase in intensity and average lifetime, a shift of the emission band to higher energies, and an increase in the emission anisotropy. Anisotropy changes have been used to determine dissociation constants for binding to these neurophysin isoforms. Based on the changes in the fluorescence properties of the dansyl probe, the dansyl group itself interacts with the protein. The degree of the dansyl-neurophysin interaction, however, appears to be different for the full sequence isoform of neurophysin I and the Val89 isoform of neurophysin II.

Crystal structure of a bovine neurophysin II dipeptide complex at 2.8 A determined from the single-wavelength anomalous scattering signal of an incorporated iodine atom

The crystal structure of a dipeptide complex of bovine neurophysin II has been solved at 2.8 A resolution solely by using single-wavelength anomalous scattering data from a single iodinated derivative. The asymmetric unit is an elongated tetramer of dimensions 110 x 40 x 30 A, composed of two dimers related by pseudo twofold symmetry. Each monomer consists of two homologous layers, each with four antiparallel beta-strands. The two regions are connected by a helix followed by a long loop. Monomer-monomer contacts involve antiparallel beta-sheet interactions, which form a dimer with two layers of eight beta-strands. One peptide per monomer occupies the principal hormone-binding pocket formed by part of the amino-terminal region and parts of the connecting helix and loop, with binding to protein consistent with conclusions drawn from solution studies. Dimer-dimer contacts involve the Tyr49 region adjacent to this site. A fifth dipeptide, of unknown biological significance, helps to stabilize one of the monomer-monomer interfaces and the tetramer-tetramer network in the crystal.

Application of peptide-mediated ring current shifts to the study of neurophysin-peptide interactions: a partial model of the neurophysin-peptide complex

Perdeuteriated peptides were synthesized that are capable of binding to the hormone binding site of neurophysin but that differ in the position of aromatic residues. The binding of these peptides to bovine neurophysin I and its des-1-8 derivative was studied by proton nuclear magnetic resonance spectroscopy in order to identify protein residues near the binding site through the observation of differential ring current effects on assignable protein resonances. Phenylalanine in position 3 of bound peptides was shown to induce significant ring current shifts in several resonances assignable to the 1-8 sequence, including those of Leu-3 and/or Leu-5, but was without effect on Tyr-49 ring protons. The magnitude of these shifts was dependent on the identity of peptide residue 1. By contrast, the sole demonstrable direct effect of an aromatic residue in position 1 was a downfield shift in Tyr-49 ring protons. Study of peptide binding to des-1-8-neurophysin demonstrated similar conformations of native and des-1-8 complexes except for the environment of Tyr-49, confirmed the peptide-induced ring current shift assignments in native neurophysin, and indicated an effect of binding on Thr-9. These observations are integrated with other results to provide a partial model of neurophysin-peptide complexes that places the ring of Tyr-49 at a distance 5-10 A from residue 1 of bound peptide and that places both the 1-8 sequence and the protein backbone region containing Tyr-49 proximal to each other and to peptide residue 3.(ABSTRACT TRUNCATED AT 250 WORDS)

Dimerization of native and proteolytically modified neurophysins as monitored by proton magnetic resonance spectroscopy: proximity of tyrosine-49 to the subunit interface

Neurophysin is a self-associating protein in which peptide-hormone binding and dimerization are thermodynamically linked. The structural basis of the linkage is unknown. We have studied the dimerization of bovine neurophysin I and two proteolytically modified derivatives by proton nuclear magnetic resonance spectroscopy in order to identify residues at the intersubunit contact regions and to evaluate the origin of the reported loss of dimerization associated with tryptic excision of residues 1-8. The concentration dependence at neural pH of the spectra of native neurophysin and des-90-92-neurophysin demonstrated a finite set of dimerization-sensitive resonances that included the ring protons of Tyr-49. Using these to monitor dimerization, we confirmed predictions of a large increase in the dimerization constant associated with carboxyl protonation. By the same criteria, dimerization of the des-1-8 protein, in disagreement with earlier reports, was found to be undiminished relative to that of the native protein. However, spectral changes in the Tyr-49 ring ortho proton region associated with dimerization of the des-1-8 protein differed significantly from those in the native protein and indicated an altered conformation of the des-1-8 dimer apparently restricted to the vicinity of Tyr-49. The results are shown to place Tyr-49 adjacent to both the intersubunit contact region and the 1-8 sequence in the native protein, loss of stabilizing interactions with 1-8 leading to altered interactions of Tyr-49 with the subunit interface. Because Tyr-49 is also close to the peptide-binding site, this arrangement spatially links the peptide-binding and dimerization sites of neurophysin.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of perdeuterated peptides in NMR studies of neurophysin-hormone interaction: demonstration of peptide-specific changes in neurophysin resonances

The effects on bovine neurophysin-I of binding the perdeuterated peptides Phe-PheNH2 and Leu-PheNH2 were compared by proton NMR. A unique difference between the two peptides in their effects on Tyr-49 ring protons indicated proximity of the Tyr-49 ring to the side-chain of position 1 of bound peptide. Non-deuterated oligopeptides containing Phe in position 3 and no methyl groups induced different changes in neurophysin methyl resonances than dipeptides, suggesting shielding of one or more protein methyl groups by Phe-3. The results demonstrate that the identity of neurophysin residues at the hormone-binding site can be probed by analysis of changes induced in the protein spectrum by systematically related NMR-transparent peptides.

Effects of peptide-binding on the proton n.m.r. spectrum of bovine neurophysin-I

The effects of binding L-phenylalanyl-L-phenylalanine amide and related peptides on the 220 MHz and 300 MHz proton n.m.r. spectra of bovine neurophysin-I were studied. Throughout both the aliphatic and aromatic proton regions, marked binding-induced changes in the protein spectrum occur which are best explained by invoking conformational change within the neurophysin dimer, in addition to direct perturbation of individual protein protons by bound peptide. In the region downfield from 6 p.p.m., a new resonance, centered at 6.45 p.p.m. was resolved in 300 MHz spectra. This resonance is tentatively assigned to a non-exchangeable -NH and undergoes a reversible binding-induced broadening. Also in this region, the binding-induced chemical shift change in the ortho ring protons of Tyr-49 was used to explore additional aspects of the kinetics of peptide-binding. The results indicate that peptides with affinities greater than or equal to 10(4) M-1 exhibit slow to intermediate exchange rates on the time scale of the Tyr-49 chemical shift change, but that fast exchange can be achieved with peptides having affinities approximately equal to 10(2) M-1.