Primary structure of alpaca growth hormone.

Reduced and carbamidomethylated alpaca growth hormone was submitted to tryptic digestion. Peptides in the mixture were purified by reverse phase HPLC and N-terminal determination and an amino acid analysis of each was performed. Data obtained and the already known primary structure of the equine growth hormone allowed the assembly-by homology-of a definite sequence of amino acids for the polypeptide chain of the protein. Present data provide further information about the relationship between growth factors.     

Nerve growth factor: structure/function relationships.

Nerve growth factor (NGF), which has a tertiary structure based on a cluster of 3 cystine disulfides and 2 very extended, but distorted beta-hairpins, is the prototype of a larger family of neurotrophins. Prior to the availability of cloning techniques, the mouse submandibular gland was the richest source of NGF and provided sufficient material to enable its biochemical characterization. It binds as a dimer to at least 2 cell-surface receptor types expressed in a variety of neuronal and non-neuronal cells. Residues involved in these interactions and in the maintenance of tertiary and quaternary structure have been identified by chemical modification and site-directed mutagenesis, and this information can be related to their location in the 3-dimensional structure. For example, interactions between aromatic residues contribute to the stability of the NGF dimer, and specific surface lysine residues participate in receptor contacts. The conclusion from these studies is that receptor interactions involve broad surface regions, which may be composed of residues from both promoters in the dimer.     

Crystal structure of human platelet-derived growth factor BB.

The crystal structure of the homodimeric BB isoform of human recombinant platelet-derived growth factor (PDGF-BB) has been determined by X-ray analysis to 3.0 A resolution. The polypeptide chain is folded into two highly twisted antiparallel pairs of beta-strands and contains an unusual knotted arrangement of three intramolecular disulfide bonds. Dimerization leads to the clustering of three surface loops at each end of the elongated dimer, which most probably form the receptor recognition sites.     

Solution structure and dynamics of epidermal growth factor and transforming growth factor alpha.

Circular dichroism (CD) and Fourier transform infrared spectroscopic studies have shown that the secondary structure of transforming growth factor alpha (TGF-alpha) is very similar to that of epidermal growth factor (EGF). The infrared spectra revealed a minor difference between the two proteins, in particular in the beta-sheet structure. A large difference was observed with CD between the two proteins in the apparent conformation each adopts when the disulfide bonds are reduced. Reduced TGF-alpha showed a distinct alpha-helical conformation only at a high trifluoroethanol concentration, whereas reduced EGF assumed an alpha-helical conformation in the absence of trifluoroethanol. This indicates that these two proteins adopt different secondary structures in the absence of disulfide bonds, although they assume similar folding structures in their presence. These data suggest that the disulfide bonds to a large degree dictate the conformation of these two proteins. Additionally, differences in the dynamic behavior between EGF and TGF-alpha were also observed. Infrared experiments showed that the hydrogen-deuterium exchange rate is much higher for TGF-alpha than for EGF, indicating that TGF-alpha is a more flexible molecule. The rate of reduction of the disulfide bonds by dithiothreitol was also faster for TGF-alpha. Therefore, it can be concluded that although EGF and TGF-alpha have a similar overall conformation, TGF-alpha is a more flexible molecule than EGF.     

Human epidermal growth factor. High resolution solution structure and comparison with human transforming growth factor alpha.

The solution structure of the 53 amino acid peptide hormone, human epidermal growth factor (hEGF), has been determined to high resolution from nuclear magnetic resonance (n.m.r.) data. A large number of internuclear distance and dihedral restraints was obtained, including data from uniformly 15N-labelled hEGF. Dynamical simulated annealing methods using the program XPLOR were used for structure calculation. An improved protocol was developed combining efficient conformational searching at a reduced computational cost. The general fold of the calculated structures compared well with that of a derivative of the carboxy-terminally truncated hEGF determined previously. A group of 44 structures were calculated with no violations greater than 0.3 A and 3 degrees for distance and dihedral restraints, respectively. The average pairwise root mean square (r.m.s.) deviation of all backbone atoms for these structures was 2.25 A for all 53 residues, 0.92 A for the bulk of the protein, and 0.23 A for the functionally important carboxy-terminal domain. Two new helical segments containing highly conserved amino acids have been identified; one between cysteines 6 and 14 and a second at the end of the carboxy-terminal domain. New insight into the molecular architecture of the site of putative receptor binding was provided by comparing the structure of hEGF with its biologically equipotent analogue, human transforming growth factor alpha. This comparison revealed a close structural relationship between the two growth factors and provides an improved understanding of the structure/function relationships in EGF.     

Peptide crystal growth via vapor diffusion. Crystal structure of glycyl-L-tyrosyl-L-alanine dihydrate.

The structure of a dihydrated form of glycyl-L-tyrosyl-L-alanine (GYA) has been determined as part of a series of peptide structural investigations and development of microscale vapor diffusion experiments for peptide crystal growth. Crystals were grown by the hanging-drop method against sodium acetate. The tripeptide is a zwitterion in the crystal, adopting an extended conformation through glycine, a nearly perpendicular bend at tyrosine and a reverse turn for the C-terminal carboxylate. Principal backbone torsion angles are psi 1 175(1) degrees, omega 2 173(1) degrees, phi 2 -119(1) degrees, psi 2 120(1) degrees, omega 3 172(1) degrees, phi 3 -73(1) degrees, psi 31 -9(1) degrees, psi 32 171(1) degrees. The tyrosyl side chain adopts an unusual orientation (chi 1/2 = -86(1) degrees). The relationship of the GYA.2H2O structure to GYA sequences in proteins is examined, particularly as regards its helix-forming potential. Crystal data: C14H19N3O4.2H2O, M(r) = 345.36, orthorhombic, P2(1)2(1)2(1), a = 4.810 (4), b = 11.400(7), c = 30.162(23)A, V = 1653.8(24)A-3, Z = 4, Dx = 1.387 Mgm-3, lambda(CuK- alpha) = 1.540 A, mu = 9.053 mm-1, F(000) = 736, T = 199 K, R = 0.041 for 1458 observations with I greater than or equal to 3 sigma(I).     

Solution structure of midkine, a new heparin-binding growth factor.

Midkine (MK) is a 13 kDa heparin-binding polypeptide which enhances neurite outgrowth, neuronal cell survival and plasminogen activator activity. MK is structurally divided into two domains, and most of the biological activities are located on the C-terminal domain. The solution structures of the two domains were determined by NMR. Both domains consist of three antiparallel beta-strands, but the C-terminal domain has a long flexible hairpin loop where a heparin-binding consensus sequence is located. Basic residues on the beta-sheet of the C-terminal domain form another heparin-binding site. Measurement of NMR signals in the presence of a heparin oligosaccharides verified that multiple amino acids in the two sites participated in heparin binding. The MK dimer has been shown to be the active form, giving signals to endothelial cells and probably to neuronal cells. We present a head-to-head dimer model of MK. The model was supported by the results of cross-linking experiments using transglutaminase. The dimer has a fused heparin-binding site at the dimer interface of the C-terminal domain, and the heparin-binding sites on MK fit the sulfate group clusters on heparin. These features are consistent with the proposed stronger heparin-binding activity and biological activity of the dimer.     

Crystal structure of human epidermal growth factor and its dimerization.

Epidermal growth factor (EGF) is a typical growth-stimulating peptide and functions by binding to specific cell-surface receptors and inducing dimerization of the receptors. Little is known about the molecular mechanism of EGF-induced dimerization of EGF receptors. The crystal structure of human EGF has been determined at pH 8.1. There are two human EGF molecules A and B in the asymmetric unit of the crystals, which form a potential dimer. Importantly, a number of residues known to be indispensable for EGF binding to its receptor are involved in the interface between the two EGF molecules, suggesting a crucial role of EGF dimerization in the EGF-induced dimerization of receptors. In addition, the crystal structure of EGF shares the main features of the NMR structure of mouse EGF determined at pH 2.0, but structural comparisons between different models have revealed new detailed features and properties of the EGF structure.     

The disulfide structure of bovine pituitary basic fibroblast growth factor.

Basic fibroblast growth factor has 4 cysteine residues in its amino acid sequence, two of which are perfectly conserved within the fibroblast growth factor family of proteins suggesting a disulfide bond at this position. Furthermore, thiol titration of bovine pituitary basic fibroblast growth factor (bFGF) indicates the presence of two free thiols, which is consistent with an intramolecular disulfide. Direct analysis of natural and recombinant fibroblast growth factor proteins have not confirmed the existence of such a disulfide. Instead, the two nonconserved cysteines of bFGF purified from bovine pituitaries are S-thiolated with glutathione. Inclusion of 75 mM N-ethylmaleimide during the homogenization of the pituitaries effectively blocks the S-thiolation, demonstrating that this modification is an artifact of the purification procedure. Analysis of the N-ethylmaleimide purified bovine pituitary bFGF suggests that the natural protein is in the correct redox state when all 4 cysteines are in the reduced form.     

Molecular weight and structure of 7 S nerve growth factor protein.

The molecular weight of 7 S nerve growth factor has been studied in the analytical ultracentrifuge between pH values 6.8 and 7.8. At pH 6.8, where no dissociation is observed, the molecular weight was found to be 137,000 plus and minus 7,000. Between pH values 7.4 and 7.8 there is some dissociation. Using the data from this study and results in the literature, a model of 7 S nerve growth factor, (alpha beta gamma)2, in reversible equilibrium with a subunit complex, (alpha beta gamma), is proposed.     

Human transforming growth factor-alpha: precursor structure and expression in E. coli

Transforming growth factor-alpha (TGF-alpha) is secreted by many human tumors and can induce the reversible transformation of nontransformed cell lines. Using long synthetic deoxyoligonucleotides as hybridization probes we isolated an exon coding for a portion of TGF-alpha from a human genomic DNA library. Utilizing this exon as a probe, a cell line derived from a human renal cell carcinoma was identified as a source of TGF-alpha mRNA. A cloned TGF-alpha cDNA was isolated from a cDNA library prepared using RNA from this cell line, and was found to encode a precursor polypeptide of 160 amino acids. The 50 amino acid mature TGF-alpha produced by expression of the appropriate coding sequence in E. coli binds to the epidermal growth factor receptor and induces the anchorage independence of normal mammalian cells in culture.