Biochemical characterization of the molecular interaction between recombinant basic fibroblast growth factor and a recombinant soluble fibroblast growth factor receptor

Pharmacological elements in clinical application of synthetic peptides

The research carried out on the biological properties of synthetic peptides and the possibility of obtaining them in adequate amounts through the recombinant DNA technology allows their use as therapeutical agents. Procedures following the synthesis of peptides must be performed in order to verify their structure, conformation, immunogenicity and biological activity and to make them suitable for clinical applications. The size of synthetic peptides together with some modifications such as amidation, acetylation and sulfatation must be taken into consideration as they may have a significant impact on half-life, stability and biological activity. Endothelial, epithelial and enzymatic interference which may hinder the absorption of drugs must be evaluated in order to choose the most appropriate route of administration. The considerable bioavailability related to the intravenous route, the effectiveness of the circulation of the intramuscular route and the possibility of reaching specific targets by the intra-arterial route must also be taken into consideration. There is the possibility of applying transdermal therapeutic systems and transdermal iontophoresis only for peptides of low molecular weight. Among synthetic peptides provided with antianaemic activity, erythropoietin, growth factors and interleukin 3 must be mentioned because of their effectiveness both in optimal stimulation of melopoiesis after chemotherapy or bone-marrow transplantation and in the treatment of anaemia occurring during chronic renal failure. Furthermore, interferon alpha was shown to be one of the most used synthetic peptides provided with antiviral and antineoplastic activity. Remarkable results have been obtained in the treatment of chronic hepatitis C, haematological malignancies and some solid tumours. More recently, interleukin 2 has been tested in the treatment of melanoma and renal cancer, inducing a reasonable proportion of overall response rate. Finally, the antagonist of gonadotropin-releasing-hormone may be regarded as effective agent both in the treatment of prostate cancer and in the inhibition of luteinizing-hormone surges during controlled ovarian stimulation. Toxic side effects can be related to the administered dose as well as to metabolites derived from bacteria in which peptides have been synthesized.

Biophysical analysis of the interaction of human ifnar2 expressed in E. coli with IFNalpha2

Type I interferons are cytokines which activate an anti-viral response by binding to two specific cell surface receptors, ifnar1 and ifnar2. Here, we report purification and refolding of the extracellular part of human ifnar2 (ifnar2-EC) expressed in Escherichia coli and its characterization with respect to its interaction with interferon alpha2 (IFNalpha2). The 25 kDa, non-glycosylated ifnar2-EC is a stable, fully active protein, which inhibits antiviral activity of IFNalpha2. The stoichiometry of binding IFNalpha2 is 1:1, as determined by gel filtration, chemical cross-linking and solid-phase detection. The affinity of this interaction is 10 nM, which is similar to the affinity measured for the cell surface-bound ifnar2 receptor. No difference in affinity was found throughout various assays using optical detection as BIAcore or reflectometric interference spectorscopy. However, the binding kinetics as measured in homogeneous phase by fluorescence de-quenching was about three times faster than that measured on a sensor surface. The rate of complex formation is relatively high compared to other cytokine-receptor interactions. The salt dependence of the association kinetics suggest a limited but significant contribution of electrostatic forces towards the rate of complex formation. The dissociation constant increases with decreasing pH according to the protonation of a base with a pKa of 6.7. The surface properties of the IFNalpha2 binding surface on ifnar2 were interpreted according to the pH and salt dependence of the interaction.

Fibroblast growth factor (FGF) soluble receptor 1 acts as a natural inhibitor of FGF2 neurotrophic activity during retinal degeneration

Fibroblast growth factors (FGF) 1 and 2 and their tyrosine kinase receptor (FGFR) are present throughout the adult retina. FGFs are potential mitogens, but adult retinal cells are maintained in a nonproliferative state unless the retina is damaged. Our work aims to find a modulator of FGF signaling in normal and pathological retina. We identified and sequenced a truncated FGFR1 form from rat retina generated by the use of selective polyadenylation sites. This 70-kDa form of soluble extracellular FGFR1 (SR1) was distributed mainly localized in the inner nuclear layer of the retina, whereas the full-length FGFR1 form was detected in the retinal Muller glial cells. FGF2 and FGFR1 mRNA levels greatly increased in light-induced retinal degeneration. FGFR1 was detected in the radial fibers of activated retinal Muller glial cells. In contrast, SR1 mRNA synthesis followed a biphasic pattern of down- and up-regulation, and anti-SR1 staining was intense in retinal pigmented epithelial cells. The synthesis of SR1 and FGFR1 specifically and independently regulated in normal and degenerating retina suggests that changes in the proportion of various FGFR forms may control the bioavailability of FGFs and thus their potential as neurotrophic factors. This was demonstrated in vivo during retinal degeneration when recombinant SR1 inhibited the neurotrophic activity of exogenous FGF2 and increased damaging effects of light by inhibiting endogenous FGF. This study highlights the significance of the generation of SR1 in normal and pathological conditions.

Analysis of protein aggregates by combination of cross-linking reactions and chromatographic separations

Chemical cross-linking provides a method that covalently bridges near-neighbour associations within proteins and protein aggregates. Combined with chromatographic separations and protein-chemical methods, it may be used to localize and to investigate three-dimensional relations as present under natural conditions. This paper reviews the chemistry and application of cross-linking reagents and the development of combination experimental approaches in view of chromatographic separations and cross-linking reactions. Investigations of homooligomeric and heterooligomeric protein associations as well as conformational analysis are presented.

Involvement of heparan sulfate and related molecules in sequestration and growth promoting activity of fibroblast growth factor

Heparan sulfate proteoglycans (HSPGs) are ubiquitous macromolecules associated with the cell surface and extracellular matrix (ECM) of a wide range of cells of vertebrate and invertebrate tissues [1, 2]. The basic HSPG structure consists of a protein core to which several linear heparan sulfate (HS) chains are covalently attached. The polysaccharide chains are typically composed of repeating hexuronic and D-glucosamine disaccharide units that are substituted to a varying extent with N- and O-linked sulfate moieties and N-linked acetyl groups [1, 2]. Beside serving as a scaffold for the attachment of various ECM components (e.g., collagen, laminin, fibronectin), the binding of HS to certain proteins has been suggested to induce a conformational change which may lead to the exposure of novel reactive determinants or conversely stabilize an inert protein configuration [1-4]. Of particular significance is the interaction of HS with fibroblast growth factors (FGFs), mediating their sequestration, stabilization and high affinity receptor binding and signaling [3-7]. Cellular responses to FGFs may hence be modulated by metabolic inhibitors of HS synthesis and sulfation, HS-degrading enzymes, and synthetic mimetics of heparin/HS. In the present review we focus on the involvement of HS in basic FGF (bFGF) receptor binding and mitogenic activity and its modulation by species of heparin, HS, and synthetic polyanionic 'heparin-mimicking' compounds. The results are discussed in relation to the current thoughts on the dual involvement of low and high affinity receptor sites in the growth promoting and angiogenic activities of bFGF and other heparin-binding growth factors.

Novel soluble, high-affinity gastrin-releasing peptide binding proteins in Swiss 3T3 fibroblasts

Swiss 3T3 cells contained substantial amounts of soluble and specific [125I]GRP binders. Like the membrane-associated GRP receptor, they were of high affinity, saturable, bound to GRP(14-27) affinity gels, and exhibited specificity for GRP(14-27) binding. They differed in that acid or freezing destroyed specific binding, specific binding exhibited different time and temperature effects, no detergent was required for their solubilization, ammonium sulfate fractionation yielded different profiles, the M(rs) were lower, GRP(1-16) also blocked binding, and a polyclonal anti-GRP receptor antiserum did not bind on Western blots. The isolated, soluble GRP binding protein(s) rapidly degraded [125I]GRP. These soluble GRP binding proteins may play a role in the regulation of the mitogenic effects of GRP on these cells.