Side-by-side dimerization of neurophysin: sedimentation velocity, viscometry, and fluorescence polarization studies

Hydrodynamics of the VanA-type VanS histidine kinase: an extended solution conformation and first evidence for interactions with vancomycin

VanA-type resistance to glycopeptide antibiotics in clinical enterococci is regulated by the VanSARA two-component signal transduction system. The nature of the molecular ligand that is recognised by the VanSA sensory component has not hitherto been identified. Here we employ purified, intact and active VanSA membrane protein (henceforth referred to as VanS) in analytical ultracentrifugation experiments to study VanS oligomeric state and conformation in the absence and presence of vancomycin. A combination of sedimentation velocity and sedimentation equilibrium in the analytical ultracentrifuge (SEDFIT, SEDFIT-MSTAR and MULTISIG analysis) showed that VanS in the absence of the ligand is almost entirely monomeric (molar mass M = 45.7 kDa) in dilute aqueous solution with a trace amount of high molar mass material (M ~ 200 kDa). The sedimentation coefficient s suggests the monomer adopts an extended conformation in aqueous solution with an equivalent aspect ratio of ~(12 ± 2). In the presence of vancomycin over a 33% increase in the sedimentation coefficient is observed with the appearance of additional higher s components, demonstrating an interaction, an observation consistent with our circular dichroism measurements. The two possible causes of this increase in s - either a ligand induced dimerization and/or compaction of the monomer are considered.

Building hydrodynamic bead-shell models for rigid bioparticles of arbitrary shape

The calculation of hydrodynamic and other solution properties of rigid macromolecules, using bead-shell model methodologies, requires the specification of the macromolecular shape in a format that can be interfaced with existing programs for hydrodynamic computations. Here, a procedure is presented for such a structural specification that is applicable to arbitrarily shaped particles. A computer program (MAKEPIXB), in which the user inserts the code needed to determine the structure, produces an structural file that is interpreted by another program (HYDROPIX) which is in charge of the computation of properties. As simple and yet illustrative examples we consider two cases: (1) dimeric structures composed of ellipsoidal subunits; and (2) toroidal structures, presenting simple equations that predict the properties of toroids with varying radial ratios.

Quantification of protein-protein interactions using fluorescence polarization

Quantitative determinations of the dissociation constants of biomolecular interactions, in particular protein-protein interactions, are essential for a detailed understanding of the molecular basis of their specificities. Fluorescence spectroscopy is particularly well suited for such studies. This article highlights the theoretical and practical aspects of fluorescence polarization and its application to the study of protein-protein interactions. Consideration is given to the nature of the different types of fluorescence probes available and the probe characteristics appropriate for the system under investigation. Several examples from the literature are discussed that illustrate different practical aspects of the technique applied to diverse systems.

Structure-function relationships of the vasopressin prohormone domains

1. In this review the structure-function relationships of the different vasopressin prohormone domains are dated and discussed, with special reference to the neurophysin and glycopeptide domains. 2. The primary structures of the currently known neurophysins and glycopeptide sequences are compared and discussed. 3. The hormone-binding and aggregational properties of neurophysin are reviewed and related to a possible function within the regulated secretory pathway. 4. It is proposed, based on the properties reviewed here as well as our own data shown here, that the sorting of the vasopressin prohormone is initiated by hormone binding, which triggers aggregation of the prohormone into the characteristic dense cores of the regulated secretory pathway. 5. This may suggest that prohormone sorting into the regulated secretory pathway is, in general, determined by noncovalent, intramolecular interactions that promote aggregation.

On the hydrodynamic analysis of macromolecular conformation

Hydrodynamics provides a powerful complementary role to the traditional "high resolution" techniques for the investigation of macromolecular conformation, especially in dilute solution, conditions which are generally inaccessible to other structural techniques. This paper describes the state of art of hydrodynamic representations for macromolecular conformation, in terms of (1) simple but straightforward ellipsoid of revolution modelling; (2) general triaxial ellipsoid modelling; (3) hydrodynamic bead modelling; (4) the ability, especially for polydisperse macromolecular systems, to distinguish between various conformation types; (5) analysis of macromolecular flexibility.

End-group modified retro-inverso isomers of tripeptide oxytocin analogues: binding to neurophysin II and enhancement of its self-association properties

The importance of peptide backbone structure in peptide/protein recognition events has been tested evaluating the binding properties of end-group modified retro-inverso isomers of MYF and LYF amides, tripeptides able to mimic oxytocin in binding neurophysin II and in potentiating its self-association. The isomers, topochemically related to their parent peptides, have been prepared respectively from all-D N-acetyl-FYM and N-acetyl-FYL amides via the Hofmann-type rearrangement mediated by iodobenzene bis-trifluoroacetate. Retro-inverso isomers recognised neurophysin II with similar affinity as the parent peptides, as determined by analytical affinity chromatography on columns prepared immobilising neurophysin II on preactivated supports. In addition, their effect on neurophysin II self-association was similar to the tripeptide oxytocin analogues, potentiating neurophysin II dimerization to the same extent, as evaluated by solid-phase binding assays on microtiter plates coated with neurophysin II. Recognition specificity of retro-inverso isomers was further demonstrated by their inhibitory effect on the interaction between neurophysin II and oxytocin tripeptide analogues. Results suggest that only the proper orientation of the alpha-amino group and of the side chains plays a dominant role in the binding of tripeptide analogues to neurophysin II and potentiation of its self-association, while the peptide backbone topology has little influence on the recognition process.

Crystals of modified bovine neurophysin II

An enzymatically modified form of bovine neurophysin II has been crystallized in three unique crystal forms. The orthorhombic form crystallizes in space group P2(1)2(1)2 with a = 15.33 nm, b = 6.92 nm, c = 3.63 nm, with four molecules in the asymmetric unit. The monoclinic form crystallizes in space group P2(1) with a = 6.22 nm, b = 9.55 nm, c = 5.45 nm and beta = 110.2 degrees, with eight molecules in the asymmetric unit. The tetragonal form crystallizes in space group P4(1)2(1)2 or P4(3)2(1)2 with a = 14.1 nm and c = 14.2 nm, with twelve molecules in the asymmetric unit. We report here the crystallization conditions, as well as the crystal data.

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)

Analysis of self-association of bovine neurophysins by gel chromatography

Analytical gel chromatography has been used to examine self-association of bovine neurophysins I and II under several sets of conditions. The data provide no evidence for associated species larger than the dimer. Association constants and Stokes radii of both monomer and dimer are very similar for both proteins in both 0.1 M KOAc, 0.16 M KCl and 0.1 M KPO4, 0.16 M KCl at pH 5.6 and 25 degrees C. The average values derived for the Stokes radii of the monomer and dimer under these conditions are 14.5 +/- 0.7 and 23.0 +/- 0.4 A, respectively. These results confirm the conclusion of Rholam and Nicolas [(1981) Biochemistry 20, 5837-5843] that the monomer and, to a lesser extent, the dimer are highly assymmetric. The Stokes radius of the monomer calculated by Rholam and Nicolas (op cit.) is approximately 30% larger than the value derived here. This discrepancy is probably the result of end-on penetration of the gel by elongated molecules [Y. Nozaki, N. M. Schechter, J. A. Reynolds, and C. Tanford (1976) Biochemistry 15, 3884-3890]. In contrast to Tellam and Winzor [(1980) Arch. Biochem. Biophys. 201, 20-24], it was found that neurophysin II does not exist solely as the dimer in 0.1 M KPO4, pH 5.6, although substitution of 0.1 M KPO4 for 0.1 M KOAc does increase the association constant by a factor of seven. Addition of 1.4 M LiCl at pH 8.1 also increases the association constant sevenfold, as well as increasing the Stokes radius of the monomer approximately 20%. The effects of ionic strength are consistent with the conclusion of Nicolas et al. [(1978) J. Biol. Chem 253, 2633-2639] that formation of the dimer depends upon hydrophobic bonding.

Transport properties of rigid, symmetrical oligomeric structures composed of prolate, ellipsoidal subunits

We have calculated translational and rotational diffusion coefficients and intrinsic viscosities of oligomeric structures composed of n identical subunits having a prolate ellipsoidal shape with axial ratio p. Results are presented for p = 1-6 for a variety of structures with n = 1-6. We compare our results with those obtained by a different modeling procedure, proposed by other workers, in which the monomeric subunit is represented as a string of touching, colinear spheres. If n and an estimate of p are known, the structure of the oligomer can be. in most cases, unambiguously determined by comparison of the experimental oligomer-to-monomer ratios of a given property with the numerical results of this work. As examples of the applicability of our results, we examine the relationship between structure and properties for neurophysin. bovine serum albumin, hemoglobin and phycocyanin.

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.

Binding of neurohypophyseal peptides to neurophysin dimer promotes formation of compact and spherical complexes

Previous hydrodynamic studies [Rholam, M., & Nicolas, P. (1981) Biochemistry 20, 5837-5843] have demonstrated that the dimerization of a neurophysin monomer (prolate ellipsoid with an axial ratio, due to asymmetry, of 5.2) results in a decreased asymmetry (axial ratio, due to asymmetry, of 3.6) as the consequence of a side-by-side association process. By a combination of hydrodynamic measurements, including the use of sedimentation velocity, viscometry, and fluorescence polarization spectroscopy, the influence of hormone binding on the shape and asymmetry properties of the neurophysin dimer was evaluated. The binding of ocytocin, vasopressin, and the tripeptide analogue of the N-terminal sequence of ocytocin, Cys(S-Me)-Tyr-Ile-NH2, results in an increase of S020,W and a decrease in both the reduced viscosity and rotational relaxation time of the bis-liganded dimeric species vs. the nonliganded form. The axial ratio (a/b) due to asymmetry of the ligand-bound dimers was found in each case to be equal to, or slightly greater than, 1.0, indicating a compact spherical shape (Stokes radius 21 A). The profound alteration on molecular dimensions observed upon ligand binding is shown to be the consequence of a ligand-induced conformational change and might explain the intradimeric binding sites positive cooperativity. It is tentatively proposed that the pseudospherical shape of the neurophysin-hormone complexes may enhance the stability of neurophysin and contribute to the prevention of leakage of neuropeptides through the membrane of neurosecretory granules. The data provide a remarkable example of a small protein with a high content in disulfide links and that undergoes conspicuous changes in conformation under the influence of nonapeptide, or tripeptide, ligands.

Folding of the mitochondrial proton adenosinetriphosphatase proteolipid channel in phospholipid vesicles

The mitochondrial H+-ATPase proteolipid from Neurospora crassa was incorporated into small unilamellar dimyristoylphosphatidylcholine vesicles and its conformation determined by circular dichroism spectroscopy (CD). While the largely alpha-helical conformation is relatively independent of the method of incorporation into vesicles, i.e., rehydration, detergent dialysis, or detergent dilution, the proteolipid conformation was significantly different in detergent micelles and in organic solvents. Only very slight changes in the CD spectrum were observed upon binding of the H+-ATPase inhibitor dicyclohexylcarbodiimide to the proteolipid in vesicles, thus suggesting that the inhibitor acts either by blocking the channel or by masking an essential charge group, rather by than causing an overall conformational change in the channel. Additionally, very similar CD spectra were obtained for vesicles with different lipid/protein mole ratios, indicating either that no substantial conformational differences exist between monomer and multimers or that monomers self-associate to form stable complexes during incorporation into vesicles. This study has provided a physical basis for model-building studies of the proteolipid channel structure.