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A class of 3,5-diphenyl-1,2,4-oxadiazole based compounds have been identified as potent sphingosine-1-phosphate-1 (S1P1) receptor agonists with minimal affinity for the S1P2 and S1P3 receptor subtypes. Analogue 26 (S1P1 IC50 = 0.6 nM) has an excellent pharmacokinetics profile in the rat and dog and is efficacious in a rat skin transplant model, indicating that S1P3 receptor agonism is not a component of immunosuppressive efficacy.

Moderately potent, selective S1P1 receptor agonists identified from high-throughput screening have been adapted into lipophilic tails for a class of orally bioavailable amino acid-based S1P1 agonists represented by 7. Many of the new compounds are potent S1P1 agonists that select against the S1P2, S1P3, and S1P4 (although not S1P5) receptor subtypes. Analogues 18 and 24 are highly orally bioavailable and possess excellent pharmacokinetic profiles in the rat, dog, and rhesus monkey.

A temperature-sensitive Saccharomyces cerevisiae mutant harboring a lesion in the ERG26 gene has been isolated. ERG26 encodes 4alpha-carboxysterol-C3 dehydrogenase, one of three enzymatic activities required for the conversion of 4,4-dimethylzymosterol to zymosterol. Gas chromatography/mass spectrometry analyses of sterols in this mutant, designated erg26-1, revealed the aberrant accumulation of a 4-methyl-4-carboxy zymosterol intermediate, as well as a novel 4-carboxysterol. Neutral lipid radiolabeling studies showed that erg26-1 cells also harbored defects in the rate of biosynthesis and steady-state levels of mono-, di-, and triglycerides. Phospholipid radiolabeling studies showed defects in the rate of biosynthesis of both phosphatidic acid and phosphatidylinositol. Biochemical studies revealed that microsomes isolated from erg26-1 cells contained greatly reduced 4alpha-carboxysterol-C3 dehydrogenase activity when compared with microsomes from wild type cells. Previous studies have shown that loss of function mutations in either of the fatty acid elongase genes SUR4/ELO3 or FEN1/GNS1/ELO2 can "bypass" the essentiality of certain ERG genes (Ladeveze, V., Marcireau, C., Delourme, D., and Karst, F. (1993) Lipids 28, 907-912; Silve, S., Leplatois, P., Josse, A., Dupuy, P. H., Lanau, C., Kaghad, M., Dhers, C., Picard, C., Rahier, A., Taton, M., Le Fur, G., Caput, D., Ferrara, P., and Loison, G. (1996) Mol. Cell. Biol. 16, 2719-2727). Studies presented here have shown that this sphingolipid-dependent "bypass" mechanism did not suppress the essential requirement for zymosterol biosynthesis. However, studies aimed at understanding the underlying physiology behind the temperature-sensitive growth defect of erg26-1 cells showed that the addition of several antifungal compounds to the growth media of erg26-1 cells could suppress the temperature-sensitive growth defect. Fluorescence microscopic analysis showed that GFP-Erg26p and GFP-Erg27p fusion proteins were localized to the endoplasmic reticulum. Two-hybrid analysis indicated that Erg25p, Erg26p, and Erg27p, which are required for the biosynthesis of zymosterol, form a complex within the cell.

Three G protein-coupled receptors (Edg-1, Edg-3, and Edg-5) for the lysolipid phosphoric acid mediator sphingosine 1-phosphate have been described by molecular cloning. Using a similar sequence that we found in the expressed sequence tag data base, we cloned and characterized of a fourth, high affinity, rat brain sphingosine 1-phosphate receptor, Edg-8. When HEK293T cells were co-transfected with Edg-8 and G protein DNAs, prepared membranes showed sphingosine 1- phosphate-dependent increases in [(35)S]guanosine 5'-(3-O-thio)triphosphate binding with an EC(50) of 90 nm. In a rat hepatoma Rh7777 cell line that exhibits modest endogenous responses to sphingosine 1-phosphate, this lipid mediator inhibited forskolin-driven rises in cAMP by greater than 90% when the cells were transfected with Edg-8 DNA (IC(50) 0.7 nm). This response is blocked fully by prior treatment of cultures with pertussis toxin, thus implicating signaling through G(i/o)alpha proteins. Furthermore, Xenopus oocytes exhibit a calcium response to sphingosine 1-phosphate after injection of Edg-8 mRNA, but only when oocytes are co-injected with chimeric G(q/i)alpha protein mRNA. Membranes from HEK293T and Rh7777 cell cultures expressing Edg-8 exhibited high affinity (K(D) = 2 nm) binding for radiolabeled sphingosine 1-phosphate. Rat Edg-8 RNA is expressed in spleen and throughout adult rat brain where in situ hybridization revealed it to be associated with white matter. Together our data demonstrate that Edg-8 is a high affinity sphingosine 1-phosphate receptor that couples to G(i/o)alpha proteins and is expressed predominantly by oligodendrocytes and/or fibrous astrocytes in the rat brain.

The plasma membrane H+-ATPase of Neurospora is a 100-kDa integral membrane protein which appears, on the basis of hydropathy analysis of its amino acid sequence, to span the lipid bilayer at least eight times. To investigate the assembly and processing of the ATPase, a full-length cDNA has been constructed for use in in vitro transcription and translation experiments. Comparison of three different forms of the ATPase (nascent protein, nascent protein cotranslationally inserted into membranes, and mature protein) revealed no difference in electrophoretic mobility. Furthermore, the nascent and mature forms gave identical peptide patterns after partial proteolysis with Staphylococcus aureus V8 protease, suggesting that the ATPase does not contain an NH2-terminal signal peptide which is cleaved upon membrane insertion. Consistent with this interpretation, the NH2-terminal peptide has been purified from a tryptic digest of the ATPase and found to lack only the initiator methionine residue; the penultimate alanine is acetylated based on analysis by fast atom bombardment mass spectroscopy. Although the ATPase contains one potential site of N-linked glycosylation, its electrophoretic mobility was unchanged following digestion with endoglycosidase H and it did not incorporate [3H]mannose or bind concanavalin A. Thus, the Neurospora plasma membrane-ATPase appears to undergo minimal post-translational processing, and its membrane insertion is probably mediated by internal sequences.

We have studied the structure of actin by measuring the relative reactivities of lysines with acetic anhydride using a competitive labeling procedure comparing monomeric globular actin. monomeric actin in the presence of salt, and filamentous actin polymerized in 100 mM NaCl and 100 mM NaCl, 2 mM MgCl2. We have identified 12 of the 19 lysines: 18, 50, 61, 68, 113, 191, 237, 290, 315, 325, 327, and 358. In all conditions, Lys (325, 327) is the most reactive. In globular actin, Lys 18, 191, 290, 314. and 358 are less than 20% as reactive as Lys (325, 327); the remaining have intermediate reactivities. On polymerization in the presence of NaCl and Mg2+, lysines 50, 61, 68, 113, and 290 become less reactive relative to Lys (325, 327). The changes in Lys 50, 61, and 113 are due largely to the polymerization event whereas those in Lys 68 and 290 appear to be an effect of Mg2+. Lys 18, 191, and 358 increase in relative reactivity when cation is added to the monomer and then become less reactive in the polymer, showing no large overall change in reactivity relative to the monomer in the absence of salt. Lysines that are reduced in reactivity upon polymerization indicate possible contact regions between actin monomers in the filament in the NH2-terminal third of the protein.

Rustmicin is a 14-membered macrolide previously identified as an inhibitor of plant pathogenic fungi by a mechanism that was not defined. We discovered that rustmicin inhibits inositol phosphoceramide synthase, resulting in the accumulation of ceramide and the loss of all of the complex sphingolipids. Rustmicin has potent fungicidal activity against clinically important human pathogens that is correlated with its sphingolipid inhibition. It is especially potent against Cryptococcus neoformans, where it inhibits growth and sphingolipid synthesis at concentrations <1 ng/ml and inhibits the enzyme with an IC50 of 70 pM. This inhibition of the membrane-bound enzyme is reversible; moreover, rustmicin is nearly equipotent against the solubilized enzyme. Rustmicin was efficacious in a mouse model for cryptococcosis, but it was less active than predicted from its in vitro potency against this pathogen. Stability and drug efflux were identified as two factors limiting rustmicin's activity. In the presence of serum, rustmicin rapidly epimerizes at the C-2 position and is converted to a gamma-lactone, a product that is devoid of activity. Rustmicin was also found to be a remarkably good substrate for the Saccharomyces cerevisiae multidrug efflux pump encoded by PDR5.

ELO2 and ELO3 were identified from the Saccharomyces cerevisiae genome data base as homologues of ELO1, a gene involved in the elongation of the fatty acid 14:0 to 16:0. Mutations in these genes have previously been shown to produce pleiotropic effects involving a number of membrane functions. The simultaneous disruption of ELO2 and ELO3 has also been shown to produce synthetic lethality, indicating that they have related and/or overlapping functions. Gas chromatography and gas chromatography/mass spectroscopy analyses reveal that null mutations of ELO2 and ELO3 produce defects in the formation of very long chain fatty acids. Analysis of the null mutants indicates that these genes encode components of the membrane-bound fatty acid elongation systems that produce the 26-carbon very long chain fatty acids that are precursors for ceramide and sphingolipids. Elo2p appears to be involved in the elongation of fatty acids up to 24 carbons. It appears to have the highest affinity for substrates with chain lengths less than 22 carbons. Elo3p apparently has a broader substrate specificity and is essential for the conversion of 24-carbon acids to 26-carbon species. Disruption of either gene reduces cellular sphingolipid levels and results in the accumulation of the long chain base, phytosphingosine. Null mutations in ELO3 result in accumulation of labeled precursors into inositol phosphoceramide, with little labeling in the more complex mannosylated sphingolipids, whereas disruption of ELO2 results in reduced levels of all sphingolipids.

In the course of screening for antifungal agents we have discovered a novel compound isolated from an endophytic fungus that inhibits fungal sphingolipid synthesis. Khafrefungin, which is composed of aldonic acid linked via an ester to a C22 modified alkyl chain, has fungicidal activity against Candida albicans, Cryptococcus neoformans, and Saccharomyces cerevisiae. Sphingolipid synthesis is inhibited in these organisms at the step in which phosphoinositol is transferred to ceramide, resulting in accumulation of ceramide and loss of all of the complex sphingolipids. In vitro, khafrefungin inhibits the inositol phosphoceramide synthase of C. albicans with an IC50 of 0.6 nM. Khafrefungin does not inhibit the synthesis of mammalian sphingolipids thus making this the first reported compound that is specific for the fungal pathway.

Gradient purified preparations of the maize 400-kDa tonoplast ATPase are enriched in two major polypeptides, 72 and 62 kDa. Polyclonal antibodies were prepared against these two putative subunits after elution from sodium dodecyl sulfate-polyacrylamide gel electrophoresis gel slices and against the solubilized native enzyme. Antibodies to both the 72- and 62-kDa polypeptides cross-reacted with similar bands on immunoblots of a tonoplast-enriched fraction from barley, while only the 72-kDa antibodies cross-reacted with tonoplast and tonoplast ATPase preparations from Neurospora. Antibodies to the 72-kDa polypeptide and the native enzyme both strongly inhibited enzyme activity, but the 62-kDa antibody was without effect. The identity and function of the subunits was further probed using radiolabeled covalent inhibitors of the tonoplast ATPase, 7-chloro-4-nitro[14C]benzo-2-oxa-1,3-diazole ([14C]NBD-Cl) and N,N'-[14C]dicyclohexylcarbodiimide ([14C]DCCD). [14C]NBD-Cl preferentially labeled the 72-kDa polypeptide, and labeling was prevented by ATP. [14C]DCCD, an inhibitor of the proton channel portion of the mitochondrial ATPase, bound to a 16-kDa polypeptide. Venturicidin blocked binding to the mitochondrial 8-kDa polypeptide but did not affect binding to the tonoplast 16-kDa polypeptide. Taken together, the results implicate the 72-kDa polypeptide as the catalytic subunit of the tonoplast ATPase. The DCCD-binding 16-kDa polypeptide may comprise the proton channel. The presence of nucleotide-binding sites on the 62-kDa polypeptide suggests that it may function as a regulatory subunit.

The H+-translocating ATPase located on vacuolar membranes of Neurospora crassa was partially purified by solubilization in two detergents, Triton X-100 and N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, followed by centrifugation on sucrose density gradients. Two polypeptides of Mr approximately equal to 70,000 and approximately equal to 62,000 consistently migrated with activity, along with several minor bands of lower molecular weight. Radioactively labeled inhibitors of ATPase activity, N-[14C]ethylmaleimide and 7-chloro-4-nitro[14C]benzo-2-oxa-1,3-diazole, labeled the Mr approximately equal to 70,000 polypeptide; this labeling was reduced in the presence of ATP. N,N'-[14C]dicyclohexylcarbodiimide labeled a polypeptide of Mr approximately equal to 15,000. Estimation of the functional size of the vacuolar membrane ATPase by radiation inactivation gave a value of Mr 5.2 X 10(5), 10-15% larger than the mitochondrial ATPase. The Neurospora vacuolar ATPase showed no crossreactivity with antiserum to plasma membrane or mitochondrial ATPase but strongly crossreacted with antiserum against a polypeptide of Mr approximately equal to 70,000 associated with the tonoplast ATPase of corn coleoptiles. These results suggest that fungal and plant vacuolar ATPases may be large multisubunit complexes, somewhat similar to, but immunologically distinct from, known F0F1 ATPases.