gramicidin-a and tetrahydrofuran

Gramicidin S (GS) is a cyclic cationic antimicrobial peptide (CAP) with a wide spectrum of antibiotic activities whose usage has been limited to topical applications owing to its cytotoxic side effects. We have synthesized tetrahydrofuran amino acid (Taa)-containing GS analogues, and we have carried out conformational analysis and explored their structure activity relationships by evaluating their antitubercular, antibacterial and cytotoxic properties. Two of these analogues showed impressive as well as selective activity against Mycobacterium tuberculosis (MTB) without toxicity towards mammalian Vero cells or human RBCs, and are promising as potential leads.

Topics: Animals; Anti-Bacterial Agents; Antitubercular Agents; Bacteria; Bacterial Infections; Chlorocebus aethiops; Erythrocytes; Furans; Gramicidin; Humans; Microbial Sensitivity Tests; Molecular Dynamics Simulation; Mycobacterium tuberculosis; Tuberculosis; Vero Cells

The response of living cells of the trabecular meshwork to synthetic ion channels is described. The THF-gramicidin hybrids THF-gram and THF-gram-TBDPS as well as a linked gA-TBDPS and gramicidin A were applied to cultured ocular trabecular meshwork cells. THF-gram application (minimal concentration, 10(-8) M; saturation, 10(-7) M) led to an additional conductance which displayed characteristics of weak Eisenman-I-selective cation channels, no cell destruction, an asymmetric change of the inward/outward currents, and higher current densities using Cs(+) as charge carrier compared to Na(+) and K(+). Linked-gA-TBDPS showed at 10(-12) M increases of the membrane conductance comparable to gA at 10(-7) M and a much faster response of the cells. Thus, THF-gramicidin hybrids form a basis for the use of synthetic ion channels in biological systems, which eventually may lead to new therapeutic approaches.

Topics: Animals; Cattle; Cesium; Electric Conductivity; Electrophysiology; Furans; Gramicidin; Ion Channels; Organosilicon Compounds; Potassium; Sodium; Structure-Activity Relationship; Trabecular Meshwork

THF-gramicidin hybrids 2-4 with the L-THF amino acid 1 in positions 11 and 12 and compounds 5-8 with the D-THF amino acid ent-1 in positions 10 and 11 were synthesized and their ion channel properties were studied by single-channel-current analysis. The replacement of positions 11 and 12 by the L-THF amino acid 1 gave a strongly reduced channel performance. In contrast, replacement of positions 10 and 11 by the D-THF amino acid ent-1 gave rise to new and interesting channel properties. For the permeability ratios, the ion selectivity shifts from Eisenman I towards Eisenman III selectivity and the channels display ms-dynamics. Most remarkable is the asymmetric compound 8, which inserts selectively into a DPhPC membrane and displays voltage-directed gating dynamics.

Topics: Amino Acid Sequence; Cations; Electric Conductivity; Furans; Gramicidin; Ion Channel Gating; Ion Channels; Lipid Bilayers; Permeability; Phospholipids; Protein Conformation; Structure-Activity Relationship

Gramicidin A (gr A), a linear pentadecapeptide containing four trp residues has been studied using steady state and time resolved fluorescence (at 298 K) and phosphorescence (at 77 K) in methanol (CH3OH), ethanol (C2H5OH), dimethyl sulfoxide (DMSO), 1,4-dioxane, 2-methyl tetrahydrofuran (2-MeTHF), ethanol/benzene (C2H5OH/C6H6) mixed solvent. Similar studies have also been carried out in CH3OH containing monovalent cations K+, Cs+, Tl+ and divalent cation Ca2+. Lambda(max) of fluorescence is found to be a good signature of the different forms having double helical structure [dh (1) to dh (4)] (J. Struct. Biol. 121 (1998) 123-141). Steady state and time resolved quenching studies of gr A by KI in CH3OH and DMSO and life time of the emitting singlet states of gr A support that gr A exists as a mixture of different forms of double helical (dh) structure [dh (1) to dh (4)] in CH3OH and as a random coil structure in DMSO. This study further indicates that emitting trp residue in DMSO is better shielded than that in CH3OH. Phosphorescence spectra of gr A at 77 K in CH3OH glass suggests that gr A retains a particular conformation dh (3) in this matrix. The phosphorescence spectra of gr A [conformation dh (4)] in 2-MeTHF at 77 K is further red shifted indicating that among all the dh forms, dh (4) has the emitting trp residue in most hydrophobic environment. The hydrophobicity of the emitting tryptophan environment is thus found to be in the order: dh (1)

Topics: Cations, Monovalent; Cesium; Dimethyl Sulfoxide; Ethanol; Furans; Gramicidin; Methanol; Solvents; Spectrometry, X-Ray Emission; Time Factors; Titanium