PubMed Health⌕ Search

Biomedical subjects

M Bhakoo

Publications and source records attributed to M Bhakoo.

7 recordsLinked to original sources

Patenting computer-designed peptides.

The problem of designing new peptides that possess specific properties, such as bactericidal activity, is of wide interest. Recently, attention has focused on the use of Computer-Aided Molecular Design techniques in parallel with more traditional 'synthesise and test' methods. These techniques may typically use Genetic Algorithms to optimise molecules based on Neural Network models that predict activity. In this paper we describe a successful application of this Molecular Design methodology that has resulted in novel bactericidal peptides of real value. A key issue for commercial utilisation of such results is the ability to protect the intellectual property rights associated with the discovery of new molecules. Typically peptide patents use structural templates of amino acid hydrophobicity-hydrophilicity that define highly regular peptide patent spaces. In an extension of established patenting practice we describe a patent application that uses a Neural Net predictive model to define the regions of peptide space that we claim within the patent. This formalism makes no a priori assumptions about the regularity of the patent space. A preliminary comparative investigation of the shape and size of this and other bactericidal peptide patent spaces is conducted.

Algorithms↗

Changes in the biocide susceptibility of Staphylococcus epidermidis and Escherichia coli cells associated with rapid attachment to plastic surfaces.

Differences in opacity between wells of a microtitre plate containing different volumes of inoculated growth medium reflected planktonic growth without any contribution from cells attached at the well surface. Simple algebra and a knowledge of the dependence of optical density upon sample path length (volume) for suspensions of differing cell density enables the generation of growth curves for attached populations (biofilms). In this manner, minimum inhibitory concentrations (MICs) were determined at various stages of growth (0-20 h), both for cells growing attached to the bases of the plate wells and, simultaneously, for cells growing in suspension above them. Biocides included cetrimide, polyhexamethylene biguanide, peracetic acid, phenoxyethanol and chloroxylenol. Results, expressed as planktonic:biofilm MIC ratios, showed susceptibility to change, not only as a function of attachment and biofilm formation, but also with respect to the nature of the chemical agent. In some instances, changes in susceptibility greater than twofold occurred immediately on attachment and could occur in the presence of biocide concentrations which exceeded the MIC.

Anti-Infective Agents, Local↗

The effect of variations in growth temperature, fatty acid composition and cholesterol content on the lipid polar head-group composition of Acholeplasma laidlawii B membranes.

We have systematically investigated the effect of variations in growth temperature, fatty acid composition and cholesterol content on the membrane lipid polar headgroup composition of Acholeplasma laidlawii B. Two important lipid compositional parameters have been determined from such an analysis. The first parameter studied was the ratio of the two major neutral glycolipids of this organism, monoglucosyldiacylglycerol (MGDG) and diglucosyldiacylglycerol (DGDG). As the former lipid prefers to exist in a reversed hexagonal phase at higher temperatures, with unsaturated fatty acyl chains or in the presence of cholesterol, the ratio of these two lipids reflects the phase state preference of the total A. laidlawii membrane lipids. Although we find that the MGDG/DGDG ratio is reduced in response to an increase in fatty acid unsaturation, increases in growth temperature or cholesterol content reduce this ratio only in cells enriched in a saturated but not an unsaturated fatty acid. The second parameter studied was the ratio of these neutral glycolipids to the only phosphatide in the A. laidlawii membrane, phosphatidylglycerol (PG); this parameter reflects the relative balance of uncharged and charged lipids in the membrane of this organism. We find that the MGDG + DGDG/PG ratio is lowest in cells enriched in the saturated fatty acid even though these cells already have the highest lipid bilayer surface charge density. Moreover, this ratio is not consistently related to growth temperature or changes in cholesterol levels, as expected. We therefore conclude that A. laidlawii strain B, apparently unlike strain A, does not possess coherent regulatory mechanisms for maintaining either the phase preference or the surface charge density of its membrane lipid constant in response to variations in growth temperature, fatty acid composition or cholesterol content.

Acholeplasma laidlawii↗

Isolation and characterization of a novel monoacylated glucopyranosyl neutral lipid from the plasma membrane of Acholeplasma laidlawii B.

The level of a normally minor component of the membrane polar lipids of Acholeplasma laidlawii B was significantly increased when the glucose supplement in the growth medium was reduced. Under such glucose-limiting conditions the proportion of this component was found to be dependent upon the fatty acid supplement and could approach 55-60% of the total polar lipids when palmitic acid was used to supplement the growth medium. A number of physical measurements, along with specific chemical and enzymic degradation studies followed by a careful analysis of the degradation products, enabled us to tentatively identify this lipid as a polyprenyl-alpha-D-glucoside with a long-chain fatty acid esterified to the 2-hydroxyl group of the sugar moiety. This lipid exhibited some unusual thermotropic phase properties and our observations suggest that it may not be easily miscible with the other membrane lipid components. The structure and physical properties of this unusual glycolipid also suggest that it may be capable of forming non-bilayer phases under physiologically relevant conditions.

Acholeplasma laidlawii↗

Interaction of Staphylococcus aureus delta-lysin with phospholipid monolayers.

The interactions of purified staphylococcal delta-lysin and melittin with various phospholipid monolayers containing different polar head groups and fatty acid moieties and with monolayers of cod and sheep erythrocyte lipids at various initial film pressures (pi i) were studied by using the Wilhelmy plate method. In each case the final increase in surface pressure (delta pi) was a linear function of pi i. In the case of delta-lysin, the critical pressures (pi c, the extrapolated values of pi i at delta pi = 0) for phosphatidylcholines with different fatty acid chain length, dipalmitoylphospholipids with different polar head groups, and cod or sheep erythrocyte total lipids fell within a relatively narrow range whereas melittin showed a much wider range. The collapse pressures of the delta-lysin and melittin films at the air-water interface when adsorbed from the hypophase were very similar. delta-Lysin showed little or no specificity in its interactions with all types of lipid films studied, whereas melittin showed preferential interaction with films of acidic lipid, similar to the specificity reported for cardiotoxins of Naja mossambica mossambica described by other workers.

Animals↗

Fatty acid and phospholipid composition of five psychrotrophic Pseudomonas spp. grown at different temperatures.

The free fatty acid and phospholipid composition of 5 psychrotrophic marine Pseudomonas spp. have been determined in chemostat culture with glucose as the limiting substrate over the range 0--20 degrees C. The predominant fatty acid present in all the isolates was hexadecenoic acid (C 16:1) together with lesser quantities of octadecenoic acid (C 18:1) whilst none contained acids with chain lengths exceeding 18 carbon atoms. Decreasing the growth temperature from 20 degrees C to 0 degrees C resulted in little significant change in fatty acid composition. The principal phospholipid components of the five psychrotrophic pseudomonads have been identified as phosphatidylserine, phosphatidylglycerol, phosphatidylethanolamine and diphosphatidylglycerol. Decreasing the growth temperature did not elicit significant changes either in the total quantities of phospholipid synthesized or in the concentration of individual phospholipid components in any of the isolates. All the psychrotrophs showed maximum glucose uptake between 15 degrees C and 20 degrees C and the rate decreased rapidly as the temperature was decreased towards 0 degrees C.

Fatty Acids↗