Spacer molecules in peptide sequences: Incorporation into analogues of atrial natriuretic factor

Improved Fmoc-solid-phase peptide synthesis of an extracellular loop of CFTR for antibody selection by the phage display technology

Cystic fibrosis (CF), a life-shortening genetic disease, is caused by mutations in the CF transmembrane conductance regulator (CFTR) gene that codes for the CFTR protein, the major chloride channel expressed at the apical membrane of epithelial cells. The development of an imaging probe capable of non-invasively detect CFTR at the cell surface could be of great advantage for the management of CF. With that purpose, we synthesized the first extracellular loop of CFTR protein (ECL1) through fluorenylmethyloxycarbonyl (Fmoc)-based microwave-assisted solid-phase peptide synthesis (SPPS), according to a reported methodology. However, aspartimide formation, a well-characterized side reaction in Fmoc-SPPS, prompted us to adopt a different side-chain protection strategy for aspartic acid residues present in ECL1 sequence. The peptide was subsequently modified via PEGylation and biotinylation, and cyclized through disulfide bridge formation, mimicking the native loop conformation in CFTR protein. Herein, we report improvements in the synthesis of the first extracellular loop of CFTR, including peptide modifications that can be used to improve antigen presentation in phage display for selection of novel antibodies against plasma membrane CFTR.

Relevance of the poly(ethylene glycol) linkers in peptide surfaces for proteases assays

Poly(ethylene glycol)s (PEGs) with different lengths were used as linkers during the preparation of peptide surfaces for protease detection. In the first approach, the PEG monolayers were prepared using a "grafting to" method on 3-aminopropyltrietoxysilane (APTES)-modified silicon wafers. Protected peptides with a fluorescent marker were synthesized by Fmoc solid phase synthesis. The protected peptide structures enabled their site-specific immobilization onto the PEG surfaces. Alternatively, the PEG-peptide surface was obtained by immobilizing a PEG-peptide conjugate directly onto the modified silicon wafer. The surfaces (composition, grafting density, hydrophilicity, and roughness) were characterized by time-of-flight-secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), contact angle (CA), and atomic force microscopy (AFM). Introducing the PEG linker between the peptide and surface increased their resistance toward nonspecific protein adsorption. The peptide surfaces were examined as analytical platforms to study the action of trypsin as a representative protease. The products of the enzymatic hydrolysis were analyzed by fluorescence spectroscopy, electrospray ionization-mass spectrometry (ESI-MS), and ToF-SIMS. Conclusions about the optimal length of the PEG linker for the analytical application of PEG-peptide surfaces were drawn. This work demonstrates an effective synthetic procedure to obtain PEG-peptide surfaces as attractive platforms for the development of peptide microarrays.

PEG-peptide conjugates

The remarkable diversity of the self-assembly behavior of PEG-peptides is reviewed, including self-assemblies formed by PEG-peptides with β-sheet and α-helical (coiled-coil) peptide sequences. The modes of self-assembly in solution and in the solid state are discussed. Additionally, applications in bionanotechnology and synthetic materials science are summarized.

New biotin derivatives for labeling and solubilizing IgG peptides

In this article, we describe the synthesis of a new class of oligoethylene-glycol based water-soluble biotin derivatives for labeling of peptides with limited solubility in aqueous solution. First 4,7,10-trioxa-1,13-tridecanediamine was mono-acetylated by succinic anhydride (Ttds) followed by the introduction of N-Fmoc-protecting group using Fmoc-N-hydroxysuccinimide ester. The resulting compound (Fmoc-Ttds) was used for the preparation of 4,7,10-trioxa-1,13-tridecanediamine di- and trimers on solid phase using Wang resin by carbodiimide coupling method. After attachment of Fmoc-Ttds to the solid support, the Fmoc-blocking group was removed and the Ttds-modified resin was repeatedly acylated by Fmoc-Ttds or by biotin using PyBOP/HOBt active ester reaction. Finally the product [Fmoc-(Ttds)(n) or biotinyl-(Ttds)(n) (where n = 1, 2 or 3)] was removed from the resin by trifluoroacetic acid in the presence of water. After appropriate HPLC purification and characterization (MS) biotinyl-(Ttds)(n) (where n = 1, 2 or 3) were introduced to the N-terminal of poorly soluble oligopeptides by solid phase peptide synthesis. We found that this new class of biotinylating reagent could be prepared easily and in good yield. Comparative solubility measurements suggest that the incorporation of these moieties-depending on the number of Ttds unit-could enhance water solubility.

Synthesis and Binding Studies of Alzheimer Ligands on Solid Support

Aminopyrazole derivatives constitute the first class of nonpeptidic rationally designed beta-sheet ligands. Here we describe a double solid-phase protocol for both synthesis and affinity testing. The presented solid-phase synthesis of four types of hybrid compounds relies on the Fmoc strategy and circumvents subsequent HPLC purification by precipitating the final product from organic solution in pure form. Hexa- and octapeptide pendants with internal di- and tetrapeptide bridges are now amenable in high yields to combinatorial synthesis of compound libraries for high-throughput screening purposes. Solid-phase peptide synthesis (SPPS) on an acid-resistant PAM allows us, after PMB deprotection, to subject the free aminopyrazole binding sites in an immobilized state to on-bead assays with fluorescence-labeled peptides. From the fluorescence emission intensity decrease, individual binding constants can be calculated via reference curves by simple application of the law of mass action. Gratifyingly, host/guest complexation can be monitored quantitatively even for those ligands, which are almost insoluble in water.

Highly sensitive detection of GG mismatched DNA by surfaces immobilized naphthyridine dimer through poly(ethylene oxide) linkers

Naphthyridine dimer is a unique molecule that strongly, and selectively, binds to the guanine-guanine mismatch in duplex DNA. We have synthesized naphthyridine dimers possessing a different length of poly(ethylene oxide) (PEO) linker, and immobilized them to CM5 sensor chip to carry out a surface plasmon resonance (SPR) assay of DNA duplexes containing a single base mismatch. The sensitivity of the sensor remarkably increased with increasing numbers of PEO units incorporated into the linker. With the sensor surface immobilized naphthyridine dimer for 1.5 x 10(3) response unit (RU) through three PEO units, the distinct SPR signal was observed at a concentration of 1 nM of the 27-mer G-G mismatch.

RGD modified polymers: biomaterials for stimulated cell adhesion and beyond

Since RGD peptides (R: arginine; G: glycine; D: aspartic acid) have been found to promote cell adhesion in 1984 (Cell attachment activity of fibronectin can be duplicated by small synthetic fragments of the molecule, Nature 309 (1984) 30), numerous materials have been RGD functionalized for academic studies or medical applications. This review gives an overview of RGD modified polymers, that have been used for cell adhesion, and provides information about technical aspects of RGD immobilization on polymers. The impacts of RGD peptide surface density, spatial arrangement as well as integrin affinity and selectivity on cell responses like adhesion and migration are discussed.

A new class of pseudopeptide antagonists of the kinin B1 receptor containing alkyl spacers

Four previously reported kinin receptor peptide antagonists, including the B1 receptor-selective peptides desArg10-HOE 140 (H-D-Arg-Arg-Pro-Hyp-Gly-Thi-Ser-D-Tic-Oic-OH) and B-9858 (H-Lys-Lys-Arg-Pro-Hyp-Gly-Igl-Ser-D-Igl-Oic-OH), have been modified by replacement of the central tetrapeptide Pro-Hyp-Gly-Xaa with linear alkyl spacers of variable length. The analogue of desArg10-HOE 140 containing the 11-aminoundecanoic acid as spacer, MEN 11575 [H-D-Arg-Arg-NH-(CH2)10-CO-Ser-D-Tic-Oic-OH], was found to be slightly more potent than the unmodified peptide (pA2 = 7.1) as a kinin B1 receptor antagonist in the rat ileum longitudinal smooth muscle assay. Moreover, MEN 11575 is devoid of residual agonist activity at the kinin B1 receptor (rat ileum) and antagonist activity at the kinin B2 receptor (guinea pig ileum longitudinal smooth muscle). Both these activities are displayed by the parent peptide desArg10-HOE 140. Therefore, despite its greatly simplified chemical structure, MEN 11575 shows an improved pharmacological profile in terms of both potency and selectivity, and it represents a good template for the development of new peptidomimetic kinin B1 receptor antagonists. We also report an attempt to investigate the conformational role of the flexible, linear spacer of MEN 11575 and to design more constrained analogues, possibly locked in the bioactive conformation, using semirigid spacers based on Calpha-tetrasubstituted alpha-amino acids of the family of 1-aminocycloalkane-1-carboxylic acids (Acnc).