PubMed · 5648994
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1968-05-18. Trimethoprim.. https://pubmed.ncbi.nlm.nih.gov/5648994/
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Aggregation or oligomerization is important for the function of many membrane peptides such as ion channels and antimicrobial peptides. However, direct proof of aggregation and the determination of the number of molecules in the aggregate have been difficult due to the lack of suitable high-resolution methods for membrane peptides. We propose a 19F spin diffusion magic-angle-spinning NMR technique to determine the oligomeric state of peptides bound to the lipid bilayer. Magnetization transfer between chemically equivalent but orientationally different 19F spins on different molecules reduces the 19F magnetization in an exchange experiment. At long mixing times, the equilibrium 19F magnetization is 1/M, where M is the number of orientationally different molecules in the aggregate. The use of the 19F spin increases the homonuclear dipolar coupling and thus the distance reach. We demonstrate this technique on crystalline model compounds with known numbers of molecules in the asymmetric unit cell, and show that 19F spin diffusion is more efficient than that of 13C by a factor of approximately 500. Application to a beta-hairpin antimicrobial peptide, protegrin-1, shows that the peptide is almost completely dimerized in POPC bilayers at a concentration of 7.4 mol %. Decreasing the peptide concentration reduced the dimer fraction. Using a monomer-dimer equilibrium model, we estimate the DeltaG for dimer formation to be -10.2 +/- 2.3 kJ/mol. This is in good agreement with the previously measured free energy reduction for partitioning and aggregating beta-sheet peptides into phospholipid membranes. This 19F spin diffusion technique opens the possibility of determining the oligomeric structures of membrane peptides.
We have investigated the structure-activity relationship of cationic amphiphilic polymethacrylate derivatives in antimicrobial and hemolytic assays. The polymers were prepared by radical copolymerizations of N-(tert-butoxycarbonyl)aminoethyl methacrylate and butyl methacrylate in the presence of methyl 3-mercaptopropionate as a chain transfer agent to give precursor polymers protected with a tert-butoxycarbonyl (Boc) group. Subsequent treatment of the Boc-protected polymers with TFA affords the desired cationic random copolymers. We examined antimicrobial and hemolytic activities of a series of polymers having a wide range of mole percentage of butyl groups (0-60%) in three different molecular weight (MW) ranges. The smallest polymers (MW < 2000) showed the lowest MIC and reduced hemolytic activity compared to that of the higher MW ones. In addition, polymers containing a high percentage of butyl groups are less selective for bacterial cells than their less hydrophobic counterparts.
In the indigenous health care delivery system of Ethiopia, numerous plant species are used to treat diseases of infectious origin. Regardless of the number of species, if any of such claims could be verified scientifically, the potential significance for the improvement of the health care services would be substantial. The objective of this study was, therefore, to determine the presence of anti-microbial activity in the crude extracts of some of the commonly used medicinal plants as well as to identify the class of compounds in the plants that were subjected to such screening. Thus, the crude methanol, petroleum ether and aqueous extracts of 67 plant species were subjected to preliminary screening against 10 strains of bacterial species and 6 fungal strains using the agar dilution method. A sample concentration of 250-2000 microg/ml and 500-4000 microg/ml were used for the bacterial and fungal pathogens, respectively. The results indicated that 44 different plant species exhibited activity against one or more of the bacteria while one species, viz., Albizzia gummifera showed activity against all the 10 bacteria at different gradient of dilution. Twenty three species inhibited or retarded growth of one or more organisms at dilution as low as 250 microg/ml. Extracts of same plants species were also tested against six different fungal pathogenic agents of which eight species showed growth inhibition against one or more of the organisms. Trichila emetica and Dovyalis abyssinica, which inhibited growth of four and five fungal strains at 100 microg/ml concentration, respectively, were the most promising plants. Chemical screening conducted on the extracts of all the plants showed the presence of several secondary metabolites, mainly, polyphenols, alkaloids, tannins sterols/terpenes, saponins and glycosides. The plants containing more of these metabolites demonstrated stronger anti-microbial properties stressing the need for further investigations using fractionated extracts and purified chemical components.