Charles E. Dahl

Stimulation of cell proliferation and polyphosphoinositide metabolism in Saccharomycescerevisiae GL7 by ergosterol

The effect of ergosterol on cell division and phospholipid metabolism was investigated in Saccharomyces cerevisiae strain GL7, a sterol and unsaturated fatty acid auxotroph. Cells growing poorly on cholesterol were stimulated to grow more rapidly by supplementing the medium with 100 ng of ergosterol per ml. Within 10 min after ergosterol addition to cells prelabeled with 32Pi or [3H]inositol the isotope content of the polyphosphoinositides increases markedly followed by an equally striking and rapid decrease. Subsequently upon continuous labeling, 32P incorporation into phosphatidylinositol and, to a lesser degree, other phospholipids increased. Finally 3h after ergosterol addition the growth rate increased. Only stimulation of the first process, i.e. polyphosphoinositide metabolism, upon ergosterol addition is resistant to inhibition by cycloheximide.

Effects of cycloartenol and lanosterol on artificial and natural membranes

Abstract Cycloartenol, a 9,19-cyclopropane sterol which is isomeric with lanosterol, showed an ability intermediate between lanosterol and cholesterol to increase the microviscosity of lecithin vesicles, to serve as a growth factor for the sterol auxotroph Mycoplasma capricolum , and to increase the microviscosity of M. capricolum membranes. The corresponding membrane effects of cyclolaudenol which contains a methyl group added to C-24 of the isooctenyl side chain of cycloartenol are more like those shown by lanosterol. We propose that the enhanced effectiveness of cycloartenol over lanosterol is due to a more favorable spatial disposition of the angular 14α-methyl group on the α-face of the molecule promoting more effective van der Waals contacts between the phospholipid fatty acyl chains and the sterol α-face. Side chain alkylation appears to perturb such contacts, reducing the effectiveness of cyclolaudenol for competent membrane function in M. capricolum .

Secondary structure and structure-activity relationships of peptides corresponding to the subunit interface of herpes simplex virus DNA polymerase

The interaction of the catalytic subunit of herpes simplex virus DNA polymerase with the processivity subunit, UL42, is essential for viral replication and is thus a potential target for antiviral drug discovery. We have previously reported that a peptide analogous to the C-terminal 36 residues of the catalytic subunit, which are necessary and sufficient for its interaction with UL42, forms a monomeric structure with partial α-helical character. This peptide and one analogous to the C-terminal 18 residues specifically inhibit UL42-dependent long chain DNA synthesis. Using multidimensional 1H nuclear magnetic resonance spectroscopy, we have found that the 36-residue peptide contains partially ordered N- and C-terminal α-helices separated by a less ordered region. A series of “alanine scan” peptides derived from the C-terminal 18 residues of the catalytic subunit were tested for their ability to inhibit long-chain DNA synthesis and by circular dichroism for secondary structure. The results identify structural aspects and specific side chains that appear to be crucial for interacting with UL42. These findings may aid in the rational design of new drugs for the treatment of herpesvirus infections.

Synthetic Peptide Vaccines for Schistosomiasis

Schistosomiasis is a chronic disease that infects an estimated 200 million persons, leading to an estimated 800,000 to 1 million annual deaths. It ranks second only to malaria in terms of morbidity and mortality caused by a parasitic disease. In addition, there is increasing evidence that schistosome infection may have profound effects on growth in children (de Lima e Costa et al., 1988; Corbett et al., 1992; McGarvey et al., 1993). Three species of schistosomes account for the vast majority of human infection: Schistosoma mansoni, found in South America, the Caribbean, Africa, and the Middle East; S. haematobium, found in Africa and the Middle East; and S. japonica, found in Asia and Southeast Asia. In addition, there are other species of schistosomes that infect humans with varying degrees of success such as S. intercalatum and S. mekongi. Disease is caused by the host immune response to parasite eggs that become trapped in tissues, forming granulomas. Granulomatous responses then lead to the development of fibrotic lesions, which in turn lead to portal hypertension, shunting, and esophageal varices. One or more of these serious disease manifestations are found in S. japonicum- and mansoni-infected patients who have developed hepatosplenic disease.

Effect of sterol incorporation on head group separation in liposomes.

Electrophoretic mobilities of multilamellar liposomes of varying composition have been measured to determine the effect of incorporated sterols on surface charge density. Liposomes made from mixtures of zwitterionic egg phosphatidylcholine (PC) and anionic egg phosphatidylglycerol (PG) in varying proportions were shown to have electrophoretic mobilities consistent with the anticipated surface charge density. Incorporation of cholesterol up to 50 mole per cent in the bilayer produced no detectable change in surface charge density. Similar results were obtained for lanosterol and epicoprostanol. These results are interpreted to mean that incorporation of the sterols into the bilayers produced no detectable change (less than 3%) in the spacing of charged phospholipids. It is inferred that sterols are incorporated among the fatty acyl chains of these phospholipid bilayers with little or no displacement of the head groups at the surface.