Crystals of a bovine neurophysin II-dipeptide amide complex

Crystals of a bovine neurophysin II tripeptide complex

A bovine neurophysin II S-methyl-Cys-Tyr-Phe-NH2 complex has been crystallized using ammonium sulfate as the precipitating agent. The crystals are orthorhombic, the space group is either I222 or I2(1)2(1)2(1) with a = 124.9 A, b = 69.6 A and c = 151.5 A. The crystals diffract to at least 3.0 A resolution. Based on one neurophysin tetramer per asymmetric unit, the Matthews coefficient is calculated to be 3.92 with a solvent content of 69%.

Crystallographic analysis of the neurophysin-oxytocin complex. A preliminary report

Single crystals of a bovine neurophysin II-oxytocin complex have been obtained using (NH4)2SO4 as the precipitating agent. The crystals diffract to at least 2.7 A resolution, belong to Laue group 4/mmm and exhibit systematic absences consistent with either space group P4(1)2(1)2 or P4(3)2(1)2. The cell dimensions are a = b = 69.07 A and c = 113.26 A. The crystals contain one neurophysin-oxytocin dimer per asymmetric unit. Based on a Vm of 2.9 A3/Da, the solvent content is calculated to be 58%. Chromatographic analysis of the dissolved crystals suggests the presence of three oxytocin molecules per neurophysin dimer.

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.

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.

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.

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.