The effects of lipids and detergents on ATPase-active P-glycoprotein

We previously isolated and characterized a partially purified preparation of ATPase-active P-glycoprotein, the multidrug transporter (Doige, C.A., Yu, X. and Sharom, F.J. (1992) Biochim. Biophys. Acta 1109, 149-160). The effect of various detergents and membrane phospholipids on the ATPase activity of P-glycoprotein has now been investigated. P-Glycoprotein ATPase activity was most stable in CHAPS, with over 50% of the activity retained at a concentration of 8 mM. Octyl glucoside in the low mM range also supported the ATPase, while deoxycholate destroyed all activity at 1 mM. Digitonin and SDS inhibited ATPase activity at very low concentrations. Triton X-100 at 2-10 microM stimulated the ATPase almost 2-fold, while higher levels inhibited activity. Although P-glycoprotein ATPase was sensitive to thermal inactivation, full activity was preserved in the presence of asolectin, but not phosphatidylcholine species. Further studies revealed that asolectin, both saturated and unsaturated phosphatidylethanolamines, and phosphatidylserine, were best able to maintain ATPase activity at 23 degrees C. Saturated phosphatidylethanolamine species activated P-glycoprotein ATPase up to 40% at 23 degrees C, and 80% at 4 degrees C. Following detergent delipidation, various lipids were able to restore P-glycoprotein ATPase activity. Unsaturated phosphatidylcholine and phosphatidylserine were most effective, while saturated species were not able to restore catalytic activity. These results indicate that membrane lipids are necessary for catalytic activity of the ATPase domains of P-glycoprotein. P-Glycoprotein has well-defined lipid preferences, with saturated phosphatidylethanolamines both activating the ATPase and providing protection from thermal inactivation, while fluid lipid mixtures are able to restore activity following delipidation.

Mutations in the cytoplasmic domain of human immunodeficiency virus type 1 transmembrane protein impair the incorporation of Env proteins into mature virions

In-frame stop codons were introduced into the coding region of human immunodeficiency virus type 1 (HIV-1) transmembrane protein (gp41). Truncation of 147 amino acids from the carboxyl terminus of gp41 (TM709) significantly decreased the stability and cell surface expression of the viral Env proteins, while truncation of 104 amino acids (TM752) did not. Truncation of 43 or more amino acids from the carboxyl terminus of gp41 generated mutant viruses which were noninfectious in several human CD4+ T lymphoid cell lines and fresh peripheral blood mononuclear cells. Analysis of the noninfectious mutant virions revealed significantly reduced incorporation of the Env proteins compared with the wild-type virions. Comparable amounts of Env proteins were detected on the surfaces of wild-type- and TM752-transfected cells, suggesting that the structures of gp41 required for efficient incorporation of Env proteins were disrupted in mutant TM752. Truncation of the last 12 amino acids (TM844) from the carboxyl terminus of gp41 did not significantly affect the assembly and release of virions or the incorporation of Env proteins into mature virions. However, the TM844 virus had dramatically decreased infectivity compared with the wild-type virus. This suggests that the cytoplasmic domain of gp41 also plays a role in other steps of virus replication.

Genotypic and antigenic identification of two new strains of spotted fever group rickettsiae isolated from China

Four isolates of spotted fever group rickettsiae isolated from ticks in China were compared with all known species and strains of spotted fever group rickettsiae by immunofluorescence assay, DNA polymerase chain reaction followed by restriction endonuclease fragment length polymorphism analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and Western immunoblot. The Chinese isolates belonged to three types, including a novel serotype which has not been described before. One isolate obtained from tick ova of Dermacentor nuttallii in Inner Mongolia was antigenically and genotypically identical to Rickettsia sibirica. Two isolates obtained from Dermacentor sinicus collected from Beijing were identical, different from other members of spotted fever group rickettsiae but apparently closely related to R. sibirica. HA-91, a strain isolated from Hyalomma asiaticum bv. kozlovi olenew, was antigenically and genotypically unique among spotted fever group rickettsiae, and we feel that data presented here should prompt consideration of it as a new species on the basis of current rickettsial taxonomy.

ATPase activity of partially purified P-glycoprotein from multidrug-resistant Chinese hamster ovary cells

In vitro studies of multidrug-resistant cell lines have shown that a membrane protein, the P-glycoprotein, is responsible for resistance to a wide range of structurally and functionally dissimilar anti-cancer drugs. The amino-acid sequence of P-glycoprotein (Pgp) indicates two consensus sequences for ATP binding and the purified protein has been reported to possess a low level of ATPase activity. As part of our goal to further characterize the ATPase activity of P-glycoprotein, we have developed a procedure for rapid partial purification of the protein in a highly active form. Plasma membrane vesicles from multidrug-resistant CHRC5 Chinese hamster ovary cells were subjected to a two-step procedure involving selective extraction with different concentrations of the zwitterionic detergent CHAPS. The resulting extract was enriched in P-glycoprotein (around 30% pure) and displayed an ATPase activity (specific activity 543 nmol mg-1 min-1) that was not found in a similar preparation from drug-sensitive cells. The ATPase specific activity was over 10-fold higher than that previously reported for immunoprecipitated Pgp and 280-fold higher than that of immunoaffinity-purified Pgp. This ATPase activity could be distinguished from that of other ion-motive ATPases and membrane-associated phosphatases and is, thus, proposed to be directly attributable to P-glycoprotein. Optimal P-glycoprotein ATPase activity required Mg2+ at an ATP: Mg2+ molar ratio of 0.75:1 and the apparent Km for ATP was 0.88 mM. P-Glycoprotein ATPase could be completely inhibited by vanadate and by the sulfhydryl-modifying reagents N-ethylmaleimide, HgCl2 and p-chloromercuribenzenesulfonate. Certain drugs and chemosensitizers, including colchicine, progesterone, nifedipine, verapamil and trifluoperazine, produced up to 50% activation of P-glycoprotein ATPase activity.

Structural data suggest that the active and inactive forms of the RecA filament are not simply interconvertible

We have used electron microscopy to examine the two major conformational states of the helical filament formed by the RecA protein of Escherichia coli. The compressed filament, formed in the absence of a nucleotide cofactor either as a self-polymer or on a single-stranded DNA molecule, is characterized in solution by about 6.1 subunits per turn of a 76 A pitch helix, and appears to be inactive with respect to all RecA activity. The active state of the filament, formed with ATP or an ATP analog on either a single or double-stranded DNA substrate, has about 6.2 subunits per turn of a 94 A pitch helix. Measurements of the contour length of RecA-covered single-stranded DNA circles in ice, formed in the absence of nucleotide cofactor, indicate that each RecA subunit binds five bases, in contrast to the three bases or base-pairs per subunit in the active state. The different stoichiometries of DNA binding suggests that the two polymeric forms are not interconvertible, as has been suggested on biochemical grounds. A three-dimensional reconstruction of the inactive state shows the same general features as the 83 A pitch filament present in the RecA crystal. This structural similarity and the fact that the crystal does not contain ATP or DNA suggests that the crystal structure is more similar to the compressed filament than the active, extended filament.

The C terminus of human immunodeficiency virus type 1 matrix protein is involved in early steps of the virus life cycle

Deletion mutations at the C terminus of the matrix (MA) protein of human immunodeficiency virus type 1 (HIV-1) were generated by site-directed mutagenesis. The resultant mutant viruses had a severe defect in virus infectivity. This defect did not involve late steps of the virus life cycle, as the synthesis and processing of the Gag polyprotein and the assembly and release of mutant virions were not greatly affected. The incorporation of viral proteins and the viral RNA genome was similar for mutant and wild-type virions. In contrast, the early steps of the virus life cycle were severely affected, as the synthesis of viral DNA postinfection was dramatically reduced in mutant-virus-infected cells. One stretch of amino acids that was deleted in one of the mutants has significant homology with a region in VP1 of the picornavirus family. This region of VP1 is presumably involved in poliovirus penetration into cells. These results suggest that in addition to its functional role in virus assembly, the MA protein of HIV-1, and possibly of other retroviruses, plays an important role in virus entry.

Elevated expression of monocyte chemoattractant protein 1 by vascular smooth muscle cells in hypercholesterolemic primates

Atherosclerosis is marked by an overt inflammatory infiltrate, with enhanced recruitment of monocytes/macrophages observed in both human and experimental atherosclerosis. We previously determined that monocyte chemoattractant protein 1 (MCP-1) accounts for virtually all of the chemotactic activity produced by vascular (aortic) smooth muscle cells in culture. We now report that arteries from a primate model of atherosclerosis with dietary-induced hypercholesterolemia exhibit increased levels of MCP-1 mRNA expression in vivo, whereas their normal counterparts demonstrate minimal MCP-1 expression. Furthermore, immunohistochemistry and in situ hybridization clearly indicate that the expression of MCP-1 protein and mRNA is in the smooth muscle cells of the medial layer of the artery and in monocyte-like and smooth muscle-like cells found in the overlying intimal lesion. These studies indicate that one of the responses to dietary hypercholesterolemia is the expression of MCP-1 by vascular smooth muscle cells. This expression, when augmented with other cellular and molecular factors, could significantly contribute to the recruitment of monocytes/macrophages to the vessel wall.

The matrix protein of human immunodeficiency virus type 1 is required for incorporation of viral envelope protein into mature virions

Accumulating evidence suggests that the matrix (MA) protein of retroviruses plays a key role in virus assembly by directing the intracellular transport and membrane association of the Gag polyprotein. In this report, we show that the MA protein of human immunodeficiency virus type 1 is also critical for the incorporation of viral Env proteins into mature virions. Several deletions introduced in the MA domain (p17) of human immunodeficiency virus type 1 Gag polyprotein did not greatly affect the synthesis and processing of the Gag polyprotein or the formation of virions. Analysis of the viral proteins revealed normal levels of Gag and Pol proteins in these mutant virions, but the Env proteins, gp120 and gp41, were hardly detectable in the mutant virions. Our data suggest that an interaction between the viral Env protein and the MA domain of the Gag polyprotein is required for the selective incorporation of Env proteins during virus assembly. Such an interaction appears to be very sensitive to conformational changes in the MA domain, as five small deletions in two separate regions of p17 equally inhibited viral Env protein incorporation. Mutant viruses were not infectious in T cells. When mutant and wild-type DNAs were cotransfected into T cells, the replication of wild-type virus was also hindered. These results suggest that the incorporation of viral Env protein is a critical step for replication of retroviruses and can be a target for the design of antiviral strategies.

Inhibition of GABA-gated chloride channel function by arachidonic acid

The effects of arachidonic acid and its metabolites on gamma-aminobutyric acid (GABAA) receptor function were determined in rat cerebral cortical synaptoneurosomes. Incubation of synaptoneurosomes with phospholipase A2 decreased muscimol-induced 36Cl- uptake. Arachidonic acid, the major unsaturated fatty acid released by phospholipase A2, also inhibited muscimol-induced 36Cl uptake. Similar inhibition was obtained with other unsaturated fatty acids (docosahexaenoic, oleic) but not with saturated fatty acids (stearic, palmitic). The effect of arachidonic acid on muscimol responses was inhibited by bovine serum albumin (BSA), and BSA enhanced muscimol responses directly, indicating the generation of endogenous arachidonic acid in the synaptoneurosome preparation. The generation of endogenous arachidonic acid was also indicated by the ability of 2 inhibitors of arachidonic acid metabolism, indomethacin and nordihydroguaiaretic acid (NDGA), to inhibit muscimol-induced 36Cl uptake. We conclude that arachidonic acid probably has both direct and indirect actions on muscimol responses since both enzyme inhibitors inhibited muscimol responses but did not prevent the effect of exogenously added arachidonic acid. In additional experiments, arachidonic acid metabolites generated by cyclooxygenase, prostaglandins D2, E2 and F2 alpha, each decreased muscimol responses; prostaglandins F2 alpha was the most potent inhibitor. Since the unsaturated fatty acids and their metabolites are most susceptible to peroxidation, a generating system of superoxide radicals was tested on muscimol responses. A combination of xanthine and xanthine oxidase inhibited muscimol-induced 36Cl uptake in a concentration-dependent manner. We propose that the inhibition of GABAA neurotransmission by arachidonic acid and its metabolites can lead to increased neuronal excitability. This mechanism may play an important role in the development of neuronal damage following seizures or cerebral ischemia.

Human papillomavirus (HPV) infection, HIV infection and cervical cancer in Tanzania, east Africa

The presence of HPV-DNA was determined in tumor biopsies of cervical-cancer patients and in cervical swabs of non-cancer patients from Tanzania, East Africa, by Southern blot hybridization and/or PCR. HPV types 16 and 18 were detected in 38% and 32%, respectively, of 50 cervical-carcinoma biopsies. A consensus primer PCR capable of detecting a broad spectrum of HPV types revealed the presence of HPV-DNA in 59% of 359 cervical swabs of non-cancer patients. Type-specific PCR showed that types 16 and 18 accounted for 13.2% and 17.5%, respectively, of all HPV infections. Therefore we concluded that HPV 18 is more prevalent in Tanzania than in any other geographical location so far reported. The strongest risk factors for the presence of any HPV-DNA in the 359 female non-cancer patients were young age and HIV infection. The epidemiology of HPV types 16 and 18 was found to differ from that of other HPV types, being associated in univariate analysis with trichomonas vaginalis infection, martial status (single/divorced), age at first intercourse, and young age at menarche. However, young age at menarche accounted for most of the effects of all other, variables in multivariate analysis. Of the non-cancer patients, 12.8% had antibodies against HIV I (no patient being severely symptomatic), and HIV infection was highly correlated with the presence of HPV-DNA, especially types 16 and 18. While HPV-DNA of any type was detectable 1.4-fold more often in HIV-positive patients than in HIV-negative patients, evidence of an infection with HPV types 16 or 18 was found 2.2-fold more often in the HIV-positive patients. The HIV-positive women did not show an increased rate of cervical cytological abnormalities as assessed by PAP staining of a single cervical smear, the overall rate of abnormalities being 2.8%. Furthermore, the age-adjusted prevalence of HIV antibodies was found to be considerably lower in 270 cervical-carcinoma patients (3% HIV-positive) in comparison with non-cancer patients. Thus there was no association observable between the prevalence of HIV infections and the frequency of cervical cytological abnormalities or cervical cancer in the setting of this cross-sectional study.

[Identification of seven snake-drugs by iso-electric point]

This paper deals with the identification of seven snake-drugs by means of iso-electric point of protein. The experimental results show that different species of snake-drugs have different iso-electric points. The experimental data are accurate and easily reproducible (CV less than 0.5%). The difference of the averages of iso-electric points of the seven snake-drugs (P less than 0.01%) is extremely significant and thus provides a scientific criterion for the identification of peeled or powdered snake-drugs.

Direct visualization of dynamics and co-operative conformational changes within RecA filaments that appear to be associated with the hydrolysis of adenosine 5'-O-(3-thiotriphosphate)

Highly co-operative structural transitions and conformational changes can be directly observed in bundles of filaments formed by the RecA protein of Escherichia coli. These filaments have been formed with RecA protein, DNA and the ATP analog adenosine 5'-O-(3-thiotriphosphate) (ATP-gamma-S). We show that while ATP-gamma-S has frequently been called non-hydrolyzable in the RecA literature, it is hydrolyzed by RecA with a kcat of about 0.01 to 0.005 min-1. This rate of ATP-gamma-S hydrolysis is significant to structural studies conducted on a time scale of hours. It has been shown that RecA subunits may be seen in different conformations within one particular form of RecA bundle. We now show that additional structural transitions take place within these bundles when they are allowed to incubate at 37 degrees C for several hours. This is the same time scale on which ATP-gamma-S is being hydrolyzed, and the suggestion that the observed structural transitions arise from the hydrolysis of ATP-gamma-S is supported by the fact that when the hydrolysis of ATP-gamma-S is inhibited (at 4 degrees C), the transitions are not observed. The transitions that occur are highly co-operative, with filaments as a whole changing their state over lengths of several thousand Angstroms. This shows that RecA filaments have an internal co-operativity, and we suggest that this is important to their function in vivo. The motions of subunits that we visualize appear to be mainly rotational, and this can be used to infer information about the motions of RecA subunits associated with the RecA ATPase that occurs during the DNA strand exchange reaction.

Cellular regulation of the benzodiazepine/GABA receptor: arachidonic acid, calcium, and cerebral ischemia

The effects of cellular mediators that contribute to ischemia-induced neuronal degeneration on gamma-aminobutyric acid (GABAA)-receptor function were studied. In vitro, phospholipase A2 (PLA2) inhibited muscimol-induced 36Cl- uptake in cerebral cortical synaptoneurosomes. The major hydrolysis product of PLA2 activity, arachidonic acid, also inhibited GABA-mediated 36Cl- uptake. The unsaturated nature of arachidonic acid makes it (and its metabolites) highly susceptible to peroxidation by oxygen radicals. Incubation of synaptoneurosomes with the superoxide radical-generating system, xanthine and xanthine oxidase, decreased muscimol-induced 36Cl- uptake, suggesting that the peroxidation of arachidonic acid and/or its metabolites interferes with GABAA-receptor function. Another factor involved in ischemia-induced neuronal degeneration is an increase in intracellular Ca2+. Calcium also inhibited GABA-mediated 36Cl- flux, consistent with its ability to activate PLA2. In contrast, Mg2+, which blocks Ca2+ channels, enhanced muscimol-induced 36Cl- uptake, consistent with its neuroprotective effects. Each of these cellular processes is activated during cerebral ischemia and can lead to neuronal degeneration. We used a model of transient forebrain ischemia in gerbils to determine if GABAA-receptor regulation is altered in vivo at a time when CA1 hippocampal cells have degenerated. Four days after a 5 minute bilateral carotid artery occlusion, receptor autoradiography was performed to measure the binding of [35S]t-butylbicyclophosphorothionate (TBPS) to the GABA-gated chloride channel. Significant decreases in TBPS binding were observed only in the dendritic layers (stratum oriens and lacunosem moleculare) of the CA1 hippocampus. The results suggest that ischemia-induced cellular processes that contribute to cell death can decrease GABA-gated chloride channels on dendrites of CA1 pyramidal cells, and that GABAA receptors may also reside on neurons afferent to or intrinsic to the dendritic layers of CA1 hippocampus.

[A clinical study of 100 cases of AIDS in Africa]

In this article, 100 cases of AIDS observed in Africa by the Chinese Medical Team are reported. The general clinical data were analyzed and studied, and the changes in the oral cavity and on the skin (Kaposi's sarcoma) are described. The results showed that oral mycotic infection and Kaposi's sarcoma are the strong evidences of this immunity deficiency and may be regarded as the early stage clinical manifestations of AIDS in Africa.

Interdependence of ryanodine binding, oligomeric receptor interactions, and Ca2+ release regulation in junctional sarcoplasmic reticulum

We have examined ryanodine binding to its receptor (RR) and compared its effect on Ca2+ release to the Ca2+ release triggered by Ca2+ plus ATP, using vesicular fragments of junctional terminal cisternae (JTC) obtained from skeletal muscle. Ryanodine binding is slow (taking hours or days to complete) and is highly temperature (Q10 = 4) and Ca2+ dependent. At equilibrium, the extent of binding increases as the concentration of ryanodine is raised above 10(-9) M, exhibiting negative cooperativity and reaching the stoichiometry of the 560,000-Da RR chains near 10(-5) M ryanodine. The specificity of the high affinity binding is demonstrated by competitive binding of ryanodine analogs. Kinetic studies using rapid filtration show that, in the absence of ryanodine, rapid (k = 15 s-1) release of Ca2+ follows a triggering exposure of loaded JTC vesicles to perfusion media containing Ca2+ plus ATP. Induction of this release has no lag period and displays minimal temperature dependence. In contrast, prolonged exposure of JTC vesicles to low (10(-7) M) ryanodine concentrations changes the JTC to a state permitting slow (k = 1 s-1) release of Ca2+ even in the absence of the Ca2+ plus ATP trigger. Higher (greater than microM) concentrations of ryanodine do not allow any Ca2+ release and prevent even the release normally triggered by Ca2+ plus ATP. Our data suggest that ryanodine binds to the open state of the tetrameric RR, inducing protein conformational changes and altered oligomeric interactions. Binding of the first molecule of ryanodine to one of the four binding sites on the receptor produces a partially closed and low conductance state of the Ca2+ release channel and reduces the ryanodine binding affinity of the remaining sites. Ryanodine occupancy of all four binding sites on the receptor completes closure of the Ca2+ channel and blocks the triggering action of Ca2+ plus ATP. The tetrameric association of the RR chains is demonstrated by crosslinking with bifunctional reagents, generating crosslinked tetramers that retain ryanodine binding and Ca2+ release functions.

Removal of the RecA C-terminus results in a conformational change in the RecA-DNA filament

The Escherichia coli RecA protein catalyzes homologous recombination of DNA molecules, and the active form of the protein is a helical polymer that it forms around DNA. Previous image analysis of electron micrographs has revealed the RecA protein to be organized into two domains or lobes within the RecA-DNA filament. We have now been able to show that a small modification of the RecA protein by proteolysis results in a significant shift in the internal mass in the RecA filament. We have cleaved approximately 18 residues from the C-terminus of the RecA protein, producing a roughly 36K MW RecA core protein that binds DNA and polymerizes normally. A three-dimensional reconstruction of this complex has been computed, and has been compared with a previous reconstruction of the intact protein. The main difference is consistent with a 15 A outward movement of the lobe that was at an inner radius in the wild-type protein. These observations yield additional evidence about the conformational flexibility of the RecA filament, and will aid in understanding the structural mechanics and dynamics of the RecA filament.