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Biomedical subjects

Mark Overhand

Publications and source records attributed to Mark Overhand.

At least 19 recordsLinked to original sources
PubMed2007

Long-range-distance NMR effects in a protein labeled with a lanthanide-DOTA chelate.

A two-thiol reactive lanthanide-DOTA (1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid) chelate, CLaNP-3 (CLaNP=caged lanthanide NMR probe), was synthesized for the rigid attachment to cysteine groups on a protein surface, and used to obtain long-range-distance information from the {15N,1H} HSQC spectra of the protein-lanthanide complex. The DOTA ring exhibits several isomers that are in exchange; however, single resonances were observed for most amide groups in the protein, allowing determination of a single, apparent magnetic-susceptibility tensor. Pseudocontact shifts caused by Yb-containing CLaNP-3 were observed for atoms at 15-35 A from the metal. By using Gd-containing CLaNP-3, relaxation effects were observed, allowing distances up to 30 A from the paramagnetic center to be determined accurately. Similar results were obtained with a Gd-DTPA (diethylene-triaminepentaacetic acid) chelate, CLaNP-1, bound in the same bidentate manner to the protein. This study demonstrates that bidentate attachment of a paramagnetic probe enables determination of long-range distances.

Chelating Agents↗
PubMed2006

Two-dimensional ordered beta-sheet lipopeptide monolayers.

A series of amphiphilic lipopeptides, ALPs, consisting of an alternating hydrophilic and hydrophobic amino acid residue sequence coupled to a phospholipid tail, was designed to form supramolecular assemblies composed of beta-sheet monolayers decorated by lipid tails at the air-water interface. A straightforward synthetic approach based on solid-phase synthesis, followed by an efficient purification protocol was used to prepare the lipid-peptide conjugates. Structural insight into the organization of monolayers was provided by surface pressure versus area isotherms, circular dichroism, Fourier transform infrared spectroscopy, and Brewster angle microscopy. In situ grazing-incidence X-ray diffraction (GIXD) revealed that lipopeptides six to eight amino acids in length form a new type of 2D self-organized monolayers that exhibit beta-sheet ribbons segregated by lipid tails. The conclusions drawn from the experimental findings were supported by a representative model based on molecular dynamics simulations of amphiphilic lipopeptides at the vacuum-water interface.

Air↗
PubMed2006

Beta-turn modified gramicidin S analogues containing arylated sugar amino acids display antimicrobial and hemolytic activity comparable to the natural product.

This paper describes the design and synthesis of gramicidin S (GS) analogues 10a-c containing arylated sugar amino acids (SAAs) as a replacement of one of the two (D)Phe-Pro beta-turn regions. The cyclic, amphiphilic peptides adopt a beta-sheet conformation featuring an unusual reverse turn induced by the SAAs. The altered turn region induces a slight distortion of the antiparallel beta-sheet, as compared to GS; the overall geometry however closely resembles that of the nonarylated GS analogue 1. GS analogues 10a-c proved to be as active as the parent GS itself as antibacterial agents and are equally efficient in lysing red blood cells. These properties are in sharp contrast to the diminished biological activity displayed by 1. We conclude that the presence of aromaticity in the turn regions of GS derivatives is required for biological activity, whereas the native conformation of the beta-hairpin is not. Our findings may guide future research toward efficient and nonhemolytic GS analogues for combating bacterial infections.

Acrylates↗
PubMed2006

Synthesis and biological evaluation of new pentaphyrin macrocycles for photodynamic therapy.

This paper describes the synthesis and in-depth characterization of two new porphyrogenic macrocycles 1 and 2, and provides an evaluation of these molecules as photosensitizer agents. By tuning the reaction conditions and starting from readily available 1,9-diformyl-5-phenyldipyrromethane (4) and tripyrrane dicarboxylic acid (3), both the nonaromatic isopentaphyrin 1, composed of a 24 pi-electron macrocycle, and the aromatic pentaphyrin 2, composed of a 22 pi-electron macrocycle, were obtained in good yield and purity. Confocal laser microscopy and cytofluorimetry studies showed that the newly synthesized pentaphyrins penetrate the cell membranes and localize mainly in the cytoplasm. In the absence of light, 1 and 2 exhibit a nonsignificant cytotoxic effect at concentrations up to 3 mug/mL. In contrast, the synthesized pentaphyrins, when delivered to cells at 1.5 or 3 microg/mL and irradiated with white light (8 mW/cm(2)), promoted a strong and dose-dependent phototoxic effect in four different cell lines. FACS and caspase-3/7 activation assays demonstrated that the pentaphyrins cause cell death by apoptosis.

Antineoplastic Agents↗
PubMed2006

Inhibitors of protein: geranylgeranyl transferases.

The enzyme protein:geranylgeranyl transferase-1 (PGGT-1 or GGTase-I) catalyzes the geranylgeranylation of cysteine residues near the C-termini of a variety of proteins, including most monomeric GTP binding precursor proteins belonging to the Rho, Rac and Rap subfamilies. These proteins are involved in signaling pathways controlling important processes such as cell differentiation and growth. In the framework of the development of therapeutics against disorders associated with aberrant cell proliferation, the interference with these signal transduction cascades has been a major focus of investigation. For instance inhibitors of PGGT-1 have shown promise in the treatment of cancer, smooth muscle hyperplasia as well as parasitic infections, such as malaria. In this review, structural and mechanistic aspects of the protein:geranylgeranyl transferases are discussed as well as their importance with respect to the terpene metabolism. An extensive summary of reported inhibitors of PGGT-1, classified as natural products, peptide substrate (Ca(1)a(2)L box), terpene substrate (geranylgeranyl pyrophosphate) and others, is presented. The few known inhibitors of the other geranylgeranylating enzyme, protein:geranylgeranyl transferase-2 (PGGT-2), are also included.

Alkyl and Aryl Transferases↗
PubMed2005

Synthesis and biological evaluation of lipophilic Ca(1)a(2)L analogues as potential bisubstrate inhibitors of protein:geranylgeranyl transferase-1.

Ca(1)a(2)L analogues, having the central dipeptide a(1)a(2) replaced by a sugar amino acid, were provided at the N-terminal end directly or via a spacer with a lipid. The inhibitory potency toward PGGT-1 of the set of lipophilic Ca(1)a(2)L analogues was improved in comparison with the original analogues, 1 and 2. The most potent inhibitors, 39 and 40, were found to inhibit PGGT-1 with an IC(50)-value of 12.7 and 12.3 microM, respectively, which is a 6-fold improvement over the corresponding analogue 1.

Alkyl and Aryl Transferases↗
PubMed2005

Synthesis and biological evaluation of gramicidin S dimers.

The design and synthesis of analogues of the cyclic beta-sheet gramicidin S (GS), having additional functionalities in their turn regions, is reported. The monomeric GS analogues were transformed into dimers and their activities towards biological membranes, through antimicriobial and hemolytic assays, were evaluated. Finally, conductivity measurements have been performed to elucidate ion channel forming properties.

Anti-Bacterial Agents↗
PubMed2004

Synthesis and application of carbohydrate-derived morpholine amino acids.

The synthesis of series of diversely functionalized epsilon-morpholine amino acids (MAAs, 5a-h) starting from an epsilon-sugar amino acid and following a two-step oxidative glycol cleavage/reductive amination strategy, is described. In an alternative synthetic scheme, diastereoisomerically pure delta-MAAs (12a,b) were obtained. Oligopeptides containing MAAs were prepared either by direct incorporation of a MAA building block or by subjecting a fully assembled SAA-containing peptide to the two-step glycol cleavage/reductive amination procedure.

Amino Acids↗
PubMed2004

A practical synthesis of gramicidin s and sugar amino Acid containing analogues.

A practical gram-scale and high-yielding synthesis of the antimicrobial peptide gramicidin S is presented. An Fmoc-based solid-phase peptide synthesis protocol is employed for the generation of the linear decapeptide precursor, which is cyclized in solution to afford the target compound. The versatility of our method is demonstrated by the construction of eight gramicidin S analogues (15a-h) having nonproteinogenic sugar amino acid residues (4-7) incorporated in the turn regions.

Amino Acids↗
PubMed2004

Design, synthesis, and evaluation of sugar amino acid based inhibitors of protein prenyl transferases PFT and PGGT-1.

Eleven analogues of the C-terminal Ca(1)a(2)X motif found in natural substrates of the prenyl transferases PFT and PGGT-1 were synthesized and evaluated for their inhibition potency and selectivity against PFT and PGGT-1. Replacement of the central dipeptide part a(1)a(2) by a benzylated sugar amino acid resulted in a good and highly selective PFT inhibitor (8, IC(50) = 250 +/- 20 nM). The methyl ester of 8 (13) selectively inhibited protein farnesylation in cultured cells.

Alkyl and Aryl Transferases↗
PubMed2003

Conformational analysis of furanoid epsilon-sugar amino acid containing cyclic peptides by NMR spectroscopy, molecular dynamics simulation, and X-ray crystallography: evidence for a novel turn structure.

Sugar amino acids (SAAs) are useful building blocks for the design of peptidomimetics and peptide scaffolds. The three-dimensional structures of cyclic hybrid molecules containing the furanoid epsilon-SAA III and several amino acids were elucidated to study the preferred conformation of such an epsilon-SAA and its conformational influence on the backbone of cyclic peptides. NMR-based molecular dynamics simulations and empirical calculations of the cyclic tetramer 1, consisting of two copies of the SAA residue and two amino acids, revealed that it is conformationally restrained. The two SAA residues adopt different conformations. One of them forms an unusual turn, stabilized by an intraresidue nine-member hydrogen bond. The methylene functionalities of the other SAA residue are positioned in such a way that an intraresidue H bond is not possible. The X-ray crystal structure of 1 strongly resembles the solution conformation. Molecular dynamics calculations in combination with NMR analysis were also performed for compounds 2 and 3, which contain the RGD (Arg-Gly-Asp) consensus sequence and were previously shown to inhibit alpha(IIb)beta(3)-receptor-mediated platelet aggregation. The biologically most active compound 2 adopts a preferred conformation with the single SAA residue folded into the nine-member H bond-containing turn. Compound 3, containing an additional valine residue, as compared with compound 2, is conformational flexible. Our studies demonstrate that the furanoid epsilon-SAA III is able to introduce an unusual intraresidue hydrogen bond-stabilized beta-turn-like conformation in two of the three cyclic structures.

Amino Acids↗
PubMed2003

Solid-phase synthesis of cyclic RGD-furanoid sugar amino acid peptides as integrin inhibitors.

The solid-phase synthesis of cyclic RGD peptides containing either one or two furanoid sugar amino acids (SAAs) is reported. Using a cyclization-cleavage approach five peptides were successfully assembled and consecutively tested on their ability to bind to the integrin receptors alpha(v)beta(3) and alpha(IIb)beta(3). The cyclic tetrapeptide c[RGD-SAA] (1) showed the most promising activity in an inhibition assay with an IC(50) of 1.49 microM for the alpha(v)beta(3) receptor and 384 nM for the alpha(IIb)beta(3) receptor.

Binding, Competitive↗
PubMed2003

Synthetic developments towards PNA-peptide conjugates.

Since the discovery of peptide nucleic acids (PNAs) as DNA mimics in the early 1990s, a tremendous effort has been directed to their application as antisense and antigene probes. With the aim of further enhancing their properties, PNAs have been conjugated to a variety of effector molecules. Among these, small peptide fragments, often derived from functional proteins, are able to convey their specific properties to the conjugate.

Ligands↗