| For medical practitioners and the general public - Cholesterol Journal Article Catalog. |
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| Stroke secondary to multiple spontaneous cholesterol emboli Pascual, M., J. M. Baumgartner, et al. (1991), Vasa 20(1): 74-7. Abstract: We describe one male, 49-year-old diabetic patient in whom regressive stroke with aphasia and right-sided hemiparesia was related to multiple small emboli in the left paraventricular cortex. Simultaneous presence of several cholesterol emboli in the left eye ground and detection of an atheromatous plaque at the homolateral carotid bifurcation let assume that the cerebral emboli originated from that plaque and also consisted of cholesterol crystals. The patient was discharged on low-dose aspirin (100 mg/day) after neurologic improvement. Follow-up at one year revealed clinical stability, recurrence of the cholesterol emboli at the eye ground examination and no change of the carotid plaque. Cholesterol embolization with renal failure, hypertension and peripheral arterial occlusions causing skin ulcerations is classical in case of atheromatous aortic disease but stroke has rarely been reported in this syndrome. However, more frequent use of invasive procedures (arteriography, transluminal angioplasty, vascular surgery) or thrombolytic treatment might increase its incidence in the near future. |
| Stroke, cholesterol and statins--are there new data about stroke prevention? Ferbert, A. (2001), Dtsch Med Wochenschr 126(22): 664-70. |
| Stroke, statins, and cholesterol. A meta-analysis of randomized, placebo-controlled, double-blind trials with HMG-CoA reductase inhibitors Blauw, G. J., A. M. Lagaay, et al. (1997), Stroke 28(5): 946-50. Abstract: BACKGROUND AND PURPOSE: To estimate the effect of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors ("statins") on stroke ris, we combined the data of the randomized, placebo-controlled, double-blind trials with HMG-CoA reductase inhibitors published so far. METHODS: The studies were identified using the Medline CD+ and Current Contents databases from January 1980 through May 1996, inclusive. All studies were evaluated on the use of a placebo control, monotherapy, and double blindness. When the type of stroke or the occurrence of clinical events or adverse effects were incompletely or not reported, the investigators were contacted personally. For each trial, the number of strokes in the treatment arm was compared with the number of strokes expected on all observations under the assumption that drug treatment had no effect. RESULTS: A total of 462 strokes among 20438 participants in 13 trials could be analyzed. A total of 181 strokes were observed in patients randomized to treatment with an HMG-CoA reductase inhibitor and 261 strokes in patients randomized to placebo. A lower than expected number of strokes was observed in the treatment groups of all but one trial (P =.001). Treatment with an HMG-CoA reductase inhibitor led to an overall risk reduction of 31% (odds ratio, 0.69; 95% confidence interval, 0.57 to 0.83). CONCLUSIONS: The combined data suggest that treatment with HMG-CoA reductase inhibitors prevents stroke in middle-aged persons. Because stroke is especially common in older age, these data reinforce the need for clinical trials to evaluate the effect of HMG-CoA reductase inhibitors in preventing stroke in the elderly. |
| Stronger suppression of plasma cholesterol and enhancement of the fecal excretion of steroids by a buckwheat protein product than by a soy protein isolate in rats fed on a cholesterol-free diet Tomotake, H., I. Shimaoka, et al. (2001), Biosci Biotechnol Biochem 65(6): 1412-4. Abstract: We investigated the effects of a buckwheat protein product (BWP), soy protein isolate (SPI) and casein on the plasma cholesterol level and fecal steroid excretion in rats fed on a cholesterol-free diet. The consumption of BWP suppressed plasma cholesterol by enhancing the fecal excretion of both neutral and acidic steroids. These effects of BWP were stronger than those of SPI. |
| Structural alterations in lecithin-cholesterol vesicles following interactions with monomeric and micellar bile salts: physical-chemical basis for subselection of biliary lecithin species and aggregative states of biliary lipids during bile formation Cohen, D. E., M. Angelico, et al. (1990), J Lipid Res 31(1): 55-70. Abstract: Using complementary physical-chemical methods including turbidimetry, quasielastic light scattering, gel filtration, and phase analysis, we examined the interactions between dilute concentrations of the common bile salt, taurochenodeoxycholate (TCDC), and uni- and multilamellar vesicles (MLVs) composed of defined molecular species of lecithin (L) and varying contents of cholesterol (Ch). Dissolution rates of MLVs with micellar TCDC, as assessed by turbidimetry, were more rapid with vesicles composed of sn-1 palmitoyl species, typical of biliary L, compared with those composed of the more hydrophobic sn-1 stearoyl species. Incorporation of Ch retarded MLV dissolution rates in proportion to the Ch content, and only at high Ch contents were dissolution rates appreciably influenced by the sn-2 fatty acid composition of L. When MLVs contained Ch in amounts characteristic of intracellular membranes (Ch/L approximately 0.1), the dissolution rates of the individual L species by TCDC accurately predicted the steady state L composition of human bile. TCDC interacted with small unilamellar L/Ch vesicles (SUVs) at concentrations well below, as well as appreciably above, its critical micellar concentration. In accordance with the TCDC-egg yolk L-H2O phase diagram, perimicellar concentrations of TCDC interacted with SUVs to form aggregates that were approximately twice the size of the SUVs. These were consistent with the formation of a dispersed hexagonal (rod-like) phase, which co-existed with aqueous bile salt (BS) monomers and either micellar or unilamellar SUV phases. Micellar TCDC completely solubilized SUVs as mixed micelles, putatively via this transient hexagonal phase. With modest Ch-supersaturation, dissolution was followed by the reemergence of a new vesicle population that coexisted metastably with mixed micelles. With high Ch supersaturation, TCDC extracted L and Ch molecules from SUVs in different proportions to form Ch-supersaturated mixed micelles and Ch-enriched SUVs, in accordance with the metastable phase diagram. These experiments are consistent with the hypothesis that sn-1 palmitoyl L species are subselected for bile, in part, by physical-chemical interactions of intracellular BS concentrations with Ch-poor membranes and that the subsequent evolution of Ch-rich vesicles and Ch-saturated mixed micelles occurs via a transitional hexagonal (rod) phase. These liquid-crystalline states are likely to be transient in Ch-unsaturated biles, but may persist in Ch-supersaturated human biles because of their high Ch contents which retard or inhibit these phase transitions. |
| Structural basis of pore formation by cholesterol-binding toxins Gilbert, R. J., J. L. Jimenez, et al. (2000), Int J Med Microbiol 290(4-5): 389-94. Abstract: In this paper we describe reconstructions by electron cryo-microscopy of two oligomeric states of the pore-forming toxin pneumolysin. The results are interpreted by the fitting of atomic models of separated domains to the 3-dimensional electron density maps, revealing two steps in the mechanism of pore formation by the family of cholesterol-binding toxins. We briefly describe the observation of the toxin pore in model membranes and contrast the apparent mechanism of pneumolysin with that of other pore-forming toxins. |
| Structural characteristics of supramolecular assemblies formed by guanidinium-cholesterol reagents for gene transfection Pitard, B., N. Oudrhiri, et al. (1999), Proc Natl Acad Sci U S A 96(6): 2621-6. Abstract: We have recently discovered that cationic cholesterol derivatives characterized by guanidinium polar headgroups are very efficient for gene transfection in vitro and in vivo. In spite of being based on some rationale at the molecular level, the development of these new synthetic vectors was nevertheless empirical. Indeed, the factors and processes underlying cationic lipid-mediated gene transfer are still poorly understood. Thus, to get a better insight into the mechanisms involved, we have examined the supramolecular structure of lipid/DNA aggregates obtained when using reagent bis(guanidinium)-tren-cholesterol (BGTC), either alone or as a liposomal formulation with the neutral phospholipid dioleoyl phosphatidylethanolamine (DOPE). We here report the results of cryotransmission electron microscopy studies and small-angle x-ray scattering experiments, indicating the presence of multilamellar domains with a regular spacing of 70 A and 68 A in BGTC/DOPE-DNA and BGTC-DNA aggregates, respectively. In addition, DNA lipoplexes with similar lamellar patterns were detected inside transfected HeLa cells by conventional transmission electron microscopy. These results suggest that DNA condensation by multivalent guanidinium-cholesterol cationic lipids involves the formation of highly ordered multilamellar domains, the DNA molecules being intercalated between the lipid bilayers. These results also invite further investigation of the intracellular fate of the internalized lipid/DNA structures during their trafficking toward the cell nucleus. The identification of the basic features of active complexes should indeed help in the design of improved guanidinium-based vectors. |
| Structural information about organized cholesterol domains from specific antibody recognition Addadi, L., M. Geva, et al. (2003), Biochim Biophys Acta 1610(2): 208-16. Abstract: Cholesterol-rich domains have been observed to exist in cell membranes under physiological and pathological conditions. Their compositions and the microenvironment of their formation vary over a wide range. Very little information is however available on the molecular structure and organization of these domains. The techniques available to provide such structural information are reviewed here first. The possibility of using tailor-made antibodies as reporters of molecular organization in membranes is then considered. The concept of antibodies recognizing molecular organization rather than single molecular epitopes is established, reviewing the existing works on antibody and protein recognition of crystalline molecular arrays. The information that such antibodies could provide in cells is finally examined together with a proof of application. |
| Structural insights into the membrane-anchoring mechanism of a cholesterol-dependent cytolysin Ramachandran, R., A. P. Heuck, et al. (2002), Nat Struct Biol 9(11): 823-7. Abstract: Perfringolysin O (PFO), a cytolytic toxin secreted by pathogenic Clostridium perfringens, forms large pores in cholesterol-containing membranes. Domain 4 (D4) of the protein interacts first with the membrane and is responsible for cholesterol recognition. By using several independent fluorescence techniques, we have determined the topography of D4 in the membrane-inserted oligomeric form of the toxin. Only the short hydrophobic loops at the tip of the D4 beta-sandwich are exposed to the bilayer interior, whereas the remainder of D4 projects from the membrane surface and is surrounded by water, making little or no contact with adjacent protein monomers in the oligomer. Thus, a limited interaction of D4 with the bilayer core seems to be sufficient to accomplish cholesterol recognition and initial binding of PFO to the membrane. Furthermore, D4 serves as the fulcrum around which extensive structural changes occur during the formation and insertion of the large transmembrane beta-barrel into the bilayer. |
| Structural mechanisms of bile salt-induced growth of small unilamellar cholesterol-lecithin vesicles Luk, A. S., E. W. Kaler, et al. (1997), Biochemistry 36(19): 5633-44. Abstract: The liver secretes cholesterol and lecithin in the form of mixed vesicles during the formation of bile. When exposed to bile salts, these metastable vesicles undergo various structural rearrangements. We have examined the effects of three different bile salts, taurocholate (TC), tauroursodeoxycholate (TUDC), and taurodeoxycholate (TDC), on the stability of sonicated lecithin vesicles containing various amounts of cholesterol. Vesicle growth was probed by turbidity measurements, quasi-elastic light scattering, and a resonance energy transfer lipid-mixing assay. Leakage of internal contents was monitored by encapsulation of fluorescence probes in vesicles. At low bile salt-to-lecithin ratios (TC/L or TUDC/L < 1), pure lecithin vesicles do not grow, but exhibit slow intervesicular mixing of lipids as well as gradual leakage. At high BS/L (TC/L or TUDC/L > 5), pure lecithin vesicles are solubilized into mixed micelles with a concomitant decrease in the overall particle size. In this regime, extensive leakage and lipid mixing occur instantaneously after exposure to bile salt. At intermediate BS/L (1 < TC/L or TUDC/L < 5), vesicles grow with time, and the rates of both leakage and lipid mixing are rapid. The data suggest that vesicles grow by the transfer of lecithin and cholesterol via diffusion in the aqueous medium. The addition of cholesterol to lecithin vesicles reduces leakage dramatically and increases the amount of BS required for complete solubilization of vesicles. The more hydrophobic TDC induces vesicle growth at a lower BS/L than does TC or TUDC. These results demonstrate the physiologic forms of lipid microstructures during bile formation and explain how the hydrophilic-hydrophobic balance of BS mixtures may profoundly affect the early stages of CH gallstone formation. |
| Structural membrane alterations in Alzheimer brains found to be associated with regional disease development; increased density of gangliosides GM1 and GM2 and loss of cholesterol in detergent-resistant membrane domains Molander-Melin, M., K. Blennow, et al. (2005), J Neurochem 92(1): 171-82. Abstract: The formation of neurotoxic beta-amyloid fibrils in Alzheimer's disease (AD) is suggested to involve membrane rafts and to be promoted, in vitro, by enriched concentrations of gangliosides, particularly GM1, and the cholesterol therein. In our study, the presence of rafts and their content of the major membrane lipids and gangliosides in the temporal cortex, reflecting late stages of AD pathology, and the frontal cortex, presenting earlier stages, has been investigated. Whole tissue and isolated detergent-resistant membrane fractions (DRMs) were analysed from 10 AD and 10 age-matched control autopsy brains. DRMs from the frontal cortex of AD brains contained a significantly higher concentration (micromol/micromol glycerophospholipids), of ganglioside GM1 (22.3 +/- 4.6 compared to 10.3 +/- 6.4, p <0.001) and GM2 (2.5 +/- 1.0 compared to 0.55 +/- 0.3, p <0.001). Similar increases of these gangliosides were also seen in DRMs from the temporal cortex of AD brains, which, in addition, comprised significantly lower proportions of DRMs. Moreover, these remaining rafts were depleted in cholesterol (from 1.5 +/- 0.2 to 0.6 +/- 0.3 micromol/micromol glycerophospholipids, p <0.001). In summary, we found an increased proportion of GM1 and GM2 in DRMs, and accelerating plaque formation at an early stage, which may gradually lead to membrane raft disruptions and thereby affect cellular functions associated with the presence of such membrane domains. |
| Structural modification of plasma HDL by phospholipids promotes efficient ABCA1-mediated cholesterol release Hajj Hassan, H., S. Blain, et al. (2005), J Lipid Res 46(7): 1457-65. Abstract: It has been suggested that ABCA1 interacts preferentially with lipid-poor apolipoprotein A-I (apoA-I). Here, we show that treatment of plasma with dimyristoyl phosphatidylcholine (DMPC) multilamellar vesicles generates prebeta(1)-apoA-I-containing lipoproteins (LpA-I)-like particles similar to those of native plasma. Isolated prebeta(1)-LpA-I-like particles inhibited the binding of (125)I-apoA-I to ABCA1 more efficiently than HDL(3) (IC(50) = 2.20 +/- 0.35 vs. 37.60 +/- 4.78 microg/ml). We next investigated the ability of DMPC-treated plasma to promote phospholipid and unesterified (free) cholesterol efflux from J774 macrophages stimulated or not with cAMP. At 2 mg DMPC/ml plasma, both phospholipid and free cholesterol efflux were increased (approximately 50% and 40%, respectively) in cAMP-stimulated cells compared with unstimulated cells. Similarly, both phospholipid and free cholesterol efflux to either isolated native prebeta(1)-LpA-I and prebeta(1)-LpA-I-like particles were increased significantly in stimulated cells. Furthermore, glyburide significantly inhibited phospholipid and free cholesterol efflux to DMPC-treated plasma. Removal of apoA-I-containing lipoproteins from normolipidemic plasma drastically reduced free cholesterol efflux mediated by DMPC-treated plasma. Finally, treatment of Tangier disease plasma with DMPC affected the amount of neither prebeta(1)-LpA-I nor free cholesterol efflux. These results indicate that DMPC enrichment of normal plasma resulted in the redistribution of apoA-I from alpha-HDL to prebeta-HDL, allowing for more efficient ABCA1-mediated cellular lipid release. Increasing the plasma prebeta(1)-LpA-I level by either pharmacological agents or direct infusions might prevent foam cell formation and reduce atherosclerotic vascular disease. |
| Structural organization of lipid phase and protein-lipid interface in apolipoprotein-phospholipid recombinants: influence of cholesterol Dergunov, A. D., J. Taveirne, et al. (1997), Biochim Biophys Acta 1346(2): 131-46. Abstract: The complexes of individual human plasma apolipoproteins (apo) A-I, E and A-II with dipalmitoylphosphatidylcholine (DPPC) in the absence or in the presence of cholesterol (Chol) were prepared with initial DPPC/Chol/protein weight ratio as 3:0.15:1. ApoA-I/DPPC/Chol complexes with different protein content (initial DPPC/apoA-I weight ratios were changed from 10.5:1 to 2.6:1) but with a fixed initial DPPC/Chol weight ratio of 20:1 were also prepared. The complexes were isolated by gel-filtration and characterized by size and composition. ApoA-I- and apoA-II-complexes had the same size (80-84 A) and the complexes became more heterogeneous upon Chol inclusion; apoE-complexes were larger (97-100 A) and more homogeneous and Chol addition had no effect on their hydrodynamic properties. Chol seems to be excluded partially in the following manner for isolated complexes with different apo's: A-II > E > A-I. The possible existence of two lipid regions in the complexes differing in lipid dynamics - the lipid shell in the vicinity of apolipoprotein (boundary lipid) opposite to the remaining part of the lipid bilayer - has been studied by absorbance and fluorescence spectroscopy with cis-parinaric acid (cis-PA) and trans-parinaric acid (trans-PA) embedded into the complexes. Their application is based on a strong preference of trans-PA for solid lipid while cis-PA distributes more equally between co-existing fluid and solid lipid regions (Sklar et al. (1979) Biochemistry 18, 1707-1716). (1) For apoA-I-complexes, the partition of cis-PA between water and lipid phase at temperatures below and above the transition temperature of DPPC (T(t)) was insensitive to Chol and temperature, while partition of trans-PA into the lipid phase of Chol-containing complex was increased at high temperature and decreased at low temperature. These results seem to be related to trans-PA redistribution between Chol-rich and protein-rich lipid domains, the latter being more disordered at T < T(t) and more immobilized at T > T(t) compared to the bulk bilayer; cis-PA localizes preferentially in boundary lipid. This hypothesis was directly confirmed by measurements of energy transfer between apoA-I tryptophanyls and probe molecules. (2) The relative response of trans-PA fluorescence intensity to temperature-induced phase transition of DPPC in apoA-I/DPPC/Chol complexes was decreased as a function of apolipoprotein content in a non-monotonic fashion with a transition midpoint at a mol ratio DPPC/A-I of 250:1, probably indicating two different modes of apolipoprotein/DPPC interaction in different sized complexes. (3) The comparative study of lipid dynamics in apoA-I-, apoE- and apoA-II-containing complexes with temperature response to phospholipid phase transition with fluorescence parameters such as intensity and anisotropy of cis-PA and trans-PA revealed the presence of boundary lipid in all three complexes without Chol. In contrast to apoA-I-containing complexes, in apoA-II/DPPC/Chol complexes, trans-PA seems to move preferentially into boundary lipid and cis-PA to distribute between two different regions probably as a result of more ordering action induced by apoA-II compared to apoA-I on the nearest phospholipid molecules in Chol-containing complexes; the apoE action on trans-PA and cis-PA distribution could be intermediate. Based on these results, the degree of Chol exclusion from the boundary lipid region for complexes with different apo's increasing in the order A-II > E > A-I can be suggested. Different Chol distributions between two lipid regions in the complexes seems not to be a function of complex size, but rather is an inherent property of the particular apolipoprotein molecule. |
| Structural, dynamic and mechanical properties of POPC at low cholesterol concentration studied in pressure/temperature space Rappolt, M., M. F. Vidal, et al. (2003), Eur Biophys J 31(8): 575-85. Abstract: We have studied the structural, dynamic and mechanical properties of 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphatidylcholine (POPC)/cholesterol binary mixtures by small-angle X-ray scattering. Our investigations were concentrated on the biologically most relevant pressure-temperature-cholesterol regime, i.e. the liquid crystalline phase and its phase boundary to the lamellar gel phase within a cholesterol concentration up to 25 mol%. From the dependence of the transition pressure we derived a value of 19 kJ/mol for the transition enthalpy Delta H(m) of POPC in excess water. With increasing cholesterol concentration, Delta H(m) drops to about 7 kJ/mol at 20 mol% cholesterol. Time-resolved pressure-scan (p-scan) and temperature-jump (T-jump) experiments reveal that at low cholesterol content (<5-8 mol%) the fluidity and also the bilayer compressibility increase remarkably. In contrast, at concentrations between 5 and 25 mol% cholesterol the bilayer becomes again more rigid and the lipid bilayer spacing increases about 2 A. Theses changes are attributed to the onset of phase separation between liquid disordered and liquid ordered phases. The fluid-fluid miscibility gap for this mono-unsaturated lecithin species is strongly enlarged compared with saturated lecithins. |
| Structure and cholesterol domain dynamics of an enriched caveolae/raft isolate Gallegos, A. M., A. L. McIntosh, et al. (2004), Biochem J 382(Pt 2): 451-61. Abstract: Despite the importance of cholesterol in the formation and function of caveolar microdomains in plasma membranes, almost nothing is known regarding the structural properties, cholesterol dynamics or intracellular factors affecting caveolar cholesterol dynamics. A non-detergent method was employed to isolate caveolae/raft domains from purified plasma membranes of murine fibroblasts. A series of fluorescent lipid probe molecules or a fluorescent cholesterol analogue, dehydroergosterol, were then incorporated into the caveolae/raft domains to show that: (i) fluorescence polarization of the multiple probe molecules diphenylhexatriene analogues, DiI18 (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate), parinaric acids and NBD-stearic acid 12-(N-methyl)-N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino-octadecanoic acid indicated that acyl chains in caveolae/raft domains were significantly less 'fluid' (i.e. more rigid) and the transbilayer 'fluidity gradient' was 4.4-fold greater than in plasma membranes; (ii) although sterol was more ordered in caveolae/raft domains than plasma membranes, spontaneous sterol transfer from caveolae/raft domains was faster (initial rate, 32%; half-time, t(1/2), 57%) than from the plasma membrane; (iii) although kinetic analysis showed similar proportions of exchangeable and non-exchangeable sterol pools in caveolae/raft domains and plasma membranes, addition of SCP-2 (sterol carrier protein-2) 1.3-fold more selectively increased sterol transfer from caveolae/raft domains by decreasing the t(1/2) (50%) and increasing the initial rate (5-fold); (iv) SCP-2 was also 2-fold more selective in decreasing the amount of non-exchangeable sterol in caveolae/raft domains compared with plasma membranes, such that nearly 80% of caveolar/raft sterol became exchangeable. In summary, although caveolae/raft lipids were less fluid than those of plasma membranes, sterol domains in caveolae/rafts were more spontaneously exchangeable and more affected by SCP-2 than those of the bulk plasma membranes. Thus caveolae/raft domains isolated without the use of detergents display unique structure, cholesterol domain kinetics and responsiveness to SCP-2 as compared with the parent plasma membrane. |
| Structure and cohesive properties of sphingomyelin/cholesterol bilayers McIntosh, T. J., S. A. Simon, et al. (1992), Biochemistry 31(7): 2012-20. Abstract: Thermal, structural, and cohesive measurements have been obtained for both bovine brain sphingomyelin (BSM) and N-tetracosanoylsphingomyelin (C24-SM) in the presence and absence of cholesterol. A goal of these experiments has been to clarify the mechanisms responsible for the strong interaction between sphingomyelin and cholesterol. Differential scanning calorimetry shows that fully hydrated bilayers of BSM and C24-SM have main endothermic phase transitions at 39 and 46 degrees C, respectively, that reflect the melting of the acyl chains from a gel to a liquid-crystalline phase. For each lipid, the addition of cholesterol monotonically reduces the enthalpy of this transition, so that at equimolar cholesterol the transition enthalpy is zero. The addition of equimolar cholesterol to either BSM or C24-SM coverts the wide-angle X-ray diffraction reflection at 4.15 A to a broad band centered at 4.5 A. Electron density profiles of gel-phase C24-SM bilayers contain two terminal methyl dips in the center of the bilayer, indicating that the lipid hydrocarbon chains partially interdigitate so that the long saturated 24-carbon acyl chains in one monolayer cross the bilayer center and appose the shorter sphingosine chains from the other monolayer. The incorporation of cholesterol adds electron density to the hydrocarbon chain region near the head group and removes the double terminal methyl dip. These wide- and low-angle X-ray data indicate that cholesterol packs into the hydrocarbon chain region near the sphingomyelin head group, fluidizes the methylene chains near the center of the bilayer compared to the gel phase, and reduces the extent of methylene chain interdigitation.(ABSTRACT TRUNCATED AT 250 WORDS) |
| Structure and function of sphingolipid- and cholesterol-rich membrane rafts Brown, D. A. and E. London (2000), J Biol Chem 275(23): 17221-4. |
| Structure and mapping of the human lanosterol 14alpha-demethylase gene (CYP51) encoding the cytochrome P450 involved in cholesterol biosynthesis; comparison of exon/intron organization with other mammalian and fungal CYP genes Rozman, D., M. Stromstedt, et al. (1996), Genomics 38(3): 371-81. Abstract: Sterol 14alpha-demethylase (P45014DM) encoded by CYP51 is a member of the cytochrome P450 (CYP) gene superfamily involved in sterol biosynthesis in fungi, plants, and animals. Constraints imposed by the specific function of CYP51 have severely limited sequence divergence in this family. Consequently, CYP51 is the only P450 family recognizable across all eukaryotic phyla. We have determined the structure of the functional human CYP51 gene, which spans 22 kb, is divided into 10 exons, and maps to 7q21.2-q21.3. The 5' portion of intron 1 is GC-rich and contains potential binding sites for several transcription factors. Primer extension studies reveal predominant transcription initiation sites in liver, kidney, lung, and placenta 250 and 249 bp upstream from the translation start site and a second major site at -100 bp. Ubiquitous expression of human CYP51 (Stromstedt et al., Arch. Biochem. Biophys. 329: 73-81, 1996), the absence of TATA and CAAT patterns, a GC-rich sequence in the promoter region, and initiation of CYP51 transcription at more than one site indicate that CYP51 is a housekeeping gene. The 5'-flanking region, exon 1, and a portion of intron 1 show the characteristics of a CpG island, with the observed/expected CpG ratio of 0.79. Sterol responsive element-like motifs were present in this region, suggesting regulation by oxysterols via a mechanism similar to that associated with other genes involved in cholesterol homeostasis. Comparison of the human CYP51 gene structure with structures of other mammalian and fungal CYP gene families shows that 7 of the 9 CYP51 introns are located at unique positions. More than 80 intron locations exist in mammalian and fungal CYP gene families, and it seems very unlikely that all these introns could have been present in the primordial CYP gene. |
| Structure and molecular mechanism of a functional form of pneumolysin: a cholesterol-dependent cytolysin from Streptococcus pneumoniae Kelly, S. J. and M. J. Jedrzejas (2000), J Struct Biol 132(1): 72-81. Abstract: One of the key steps in understanding human disease arising from gram-positive bacteria lies in the mechanisms of the cholesterol-dependent cytolysins (CDCs). Pneumolysin (PLY), a CDC from Streptococcus pneumoniae, is of special importance due to the severe impacts of pneumococcal infections on mortality and morbidity worldwide. We have overexpressed, purified, and characterized PLY in its fully functional complex form with the enzyme bound to its receptor activator on target cells, cholesterol. The circular dichroism studies of PLY in solution with an excess of cholesterol show a change in the far UV spectrum consistent with a decrease in the beta-sheet and an increase in the random coil structures of the enzyme. Pore formation in membranes leading to cell lysis is the functional target for this cytolysin. The sedimentation velocity and equilibrium analyses of the cholesterol-bound enzyme show hydrodynamic properties different from those of the cholesterol-free form. The soluble form of the cholesterol-free enzyme exists in solution as a mixture of monomers and dimers, whereas the cholesterol-bound form exists only as a monomer. A mechanism of formation of PLY pores in the lipid bilayer of the target cells is discussed. |
| Structure and pseudosymmetry of cholesterol at 310 K Hsu, L. Y., J. W. Kampf, et al. (2002), Acta Crystallogr B 58(Pt 2): 260-4. Abstract: The structure of cholesterol above the (304.8 K) phase transition, previously published in preliminary form Hsu & Nordman (1983). Science, 220, 604-606, has been fully refined using augmented X-ray data. The crystals are triclinic, space group P1, with (reassigned) cell parameters a = 27.565 (10), b = 38.624 (16), c = 10.748 (4) A, alpha = 93.49 (3), beta = 90.90 (3), gamma = 117.15 (3) degrees, and V = 10151 (7) A(3). The unit cell contains Z = 16 molecules, of which eight are related to the other eight by unusual twofold rotational pseudosymmetry. The structure is related to the room-temperature phase, with Z = 8, by a rearrangement of some of the molecules, and by a doubling of the a axis. |