Sterol structure and sphingomyelin acyl chain length modulate lateral packing elasticity and detergent solubility in model membranes.
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):.Sterol structure and sphingomyelin acyl chain length modulate lateral packing elasticity and detergent solubility in model membranes.1, , , .1The Hormel Institute, University of Minnesota, Austin, Minnesota , USA.AbstractMembrane microdomains, such as caveolae and rafts, are enriched in cholesterol and sphingomyelin, display liquid-ordered phase properties, and putatively function as protein organizing platforms. The goal of this investigation was to identify sterol and sphingomyelin structural features that modulate surface compression and solubilization by detergent because liquid-ordered phase displays low lateral elasticity and resists solubilization by Triton X-100. Compared to cholesterol, sterol structural changes involved either altering the polar headgroup (e.g., 6-ketocholestanol) or eliminating the isooctyl hydrocarbon tail (e.g., 5-androsten-3beta-ol). Synthetic changes to sphingomyelin resulted in homogeneous acyl chains of differing length but of biological relevance. Using a Langmuir surface balance, surface compressional moduli were assessed at various surface pressures including those (pi & or =30 mN/m) that mimic biomembrane conditions. Sphingomyelin-sterol mixtures generally were less elastic in a lateral sense than chain-matched phosphatidylcholine-sterol mixtures at equivalent high sterol mole fractions. Increasing content of 6-ketocholestanol or 5-androsten-3beta-ol in sphingomyelin decreased lateral elasticity but much less effectively than cholesterol. Our results indicate that cholesterol is ideally structured for maximally reducing the lateral elasticity of membrane sphingolipids, for enabling resistance to Triton X-100 solubilization, and for interacting with sphingomyelins that contain saturated acyl chains similar in length to their sphingoid bases.PMID:
[PubMed - indexed for MEDLINE] PMCID: PMC1303681 Structural features of cholesterol, androsterol, 6-ketocholestanol, sphingomyelin (SM), and phosphatidylcholine (PC). Blue centers represent nitrogen atoms and red centers represent oxygen atoms. For simplicity, lipid hydrocarbon chains are depicted as fully extended trans rotamers. In reality, free rotation about the carbon-carbon single bonds produces trans-gauche isomers which are more numerous in the fluid state than in the gel state. Chain-matching of PC and SM is best achieved when PC contains a myristoyl sn-1 chain, as illustrated for 18:0 SM and 14:0–18:0 PC. Long saturated acyl chains (e.g., 24:0) produce chain length asymmetry within the SM molecule (arrow).Biophys J. ):.Monolayer behavior of androsterol mixed with 16:0 SM, 14:0–16:0 PC, 18:0 SM, or 14:0–18:0 PC. Data were collected using the automated Langmuir-type film balance described in text. (Upper panels) Surface pressure vs. average molecular area isotherms. (Lower panels) Surface compressional modulus
vs. average molecular area. Mole fraction of sterol (from right to left), 0 (———), 0.1 (- - -), 0.2 (····), 0.3 (-·-), 0.4 (-··-), 0.5 (….), and 0.6 (——). Isotherms of cholesterol mixed with these same species of SM and PC have been reported previously (Li et al., 2001, Figs. 2 and 3).Biophys J. ):.Monolayer behavior of 6-ketocholestanol mixed with 16:0 SM, 14:0–16:0 PC, 18:0 SM, or 14:0–18:0 PC. Other details are the same as in the Fig. 2 legend.Biophys J. ):.Surface compressional moduli
vs. sterol mole fraction analyses. (A) 16:0 SM/ (B) 14:0–16:0 PC/ (C) 18:0 SM/ and (D) 14:0–18:0 PC/androsterol. The different symbols represent values calculated from experimental data at the following surface pressures: 5 mN/m (o), 15 mN/m (?), and 30 mN/m (?). Solid lines represent predicted response assuming additivity of individual lipid components (see text). Values for mixtures of cholesterol with these same species of SM and PC have been reported previously (Li et al., 2001, Fig. 6).Biophys J. ):.Surface compressional moduli
vs. sterol mole fraction analyses. (A) 16:0 SM/6- (B) 14:0–16:0 PC/6- (C) 18:0 SM/6- and (D) 14:0–18:0 PC/6-ketocholestanol mixed monolayers. The different symbols represent values calculated from experimental data at the following surface pressures: 5 mN/m (o), 15 mN/m (?), and 30 mN/m (?). Solid lines represent predicted response assuming additivity of individual lipid components (see Materials and Methods).Biophys J. ):.Monolayer behavior of different sterols mixed with 24:0 SM. (Upper panels) Surface pressure versus average molecular area isotherms. (Lower panels) Surface compressional modulus
vs. average molecular area. (A, B) 24:0 SM/ (C, D) 24:0 SM/6- and (E, F) 24:0 SM/cholesterol mixed monolayers. Mole fraction of sterol (from right to left), 0 (———), 0.1 (- - -), 0.2 (····), 0.3 (- · -), 0.4 (- ·· -), 0.5 (….), and 0.6 (——).Biophys J. ):.Monolayer behavior of different sterols mixed with 26:0 SM. (Upper panels) Surface pressure versus average molecular area isotherms. (Lower panels) Surface compressional modulus
vs. average molecular area. (A, B) 26:0 SM/ (C, D) 26:0 SM/6- and (E, F) 26:0 SM/cholesterol mixed monolayers. Mole fraction of sterol (from right to left), 0 (———), 0.1 (- - -), 0.2 (····), 0.3 - · -), 0.4 (- · · -), 0.5 (….), and 0.6 (——).Biophys J. ):.Surface compressional moduli
vs. sterol mole fraction for mixed monolayers. (A) Cholesterol/24:0 SM; (B) Cholesterol/26:0 SM; (C) 6-ketocholestanol/24:0 SM; (D) 6-ketocholestanol/26:0 SM; (E) androsterol/24:0 SM; and (F) androsterol/26:0 SM. The different symbols represent values calculated from experimental data at the following surface pressures: 5 mN/m (o), 15 mN/m (?), and 30 mN/m (?). Solid lines represent predicted response assuming additivity of individual lipid components (see Materials and Methods).Biophys J. ):.Comparison of monolayer surface compressional moduli
and bilayer detergent insolubility of lipid mixtures composed of different sterols and SM or PC species. (Upper panels) Surface compressional modulus
vs. sterol mole fraction at 30 mN/m and 24°C. (Lower panels) Percent optical density remaining vs. sterol mole fraction at 24°C. Symbols correspond to: 16:0 SM, (o), 14:0–16:0 PC (○),18:0 SM (?), 14:0–18:0 PC (?), and 24:0 SM (?), mixed with the indicated amount of androsterol (A and B), 6-ketocholestanol (C and D), or cholesterol (E and F). The data for 24:0 SM in E and F were not part of the figure published previously (Li et al., 2001).Biophys J. ):.Publication TypesMeSH TermsSubstancesGrant SupportFull Text SourcesMolecular Biology DatabasesMiscellaneous
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External link. Please review our .Lateral column length in adult flatfoot deformity.
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):392-7. doi: 10.. Epub
2013 Jan 15.Lateral column length in adult flatfoot deformity.1, , .1University of Southern California-Keck School of Medicine, Los Angeles, CA, USA.AbstractINTRODUCTION: In adult acquired flatfoot deformity, it is unclear whether the lateral column length shortens with progression of the deformity, whether it is short to begin with, or whether it is short at all. To our knowledge, no previous study has examined the lateral column length of patients with adult acquired flatfoot deformity compared to a control population. The purpose of our study was to compare the lateral column length in patients with and without adult acquired flatfoot deformity to see if there was a significant difference.METHODS: The study was a retrospective radiographic review of 2 foot and ankle fellowship-trained orthopaedic surgeons' patients with adult flatfoot deformity. Our study population consisted of 75 patients, 85 feet (28 male, 57 female) with adult flatfoot deformity with a mean age of 64 (range, 23-93). Our control population consisted of 57 patients and 70 feet (23 male, 47 female) without flatfoot deformity with a mean age of 61 (range, 40-86 years). Weightbearing anteroposterior (AP) and lateral foot radiographs were analyzed for each patient, and the following measurements were made: medial and lateral column lengths, talonavicular uncoverage angle, talus-first metatarsal angle, calcaneal pitch angle, and medial and lateral column heights. An unpaired t test was used to analyze the measurements between the groups. Ten patients' radiographs were remeasured, and correlation coefficients were obtained to assess the reliability of the measuring techniques.RESULTS: For the flatfoot group, the mean medial and lateral column lengths on the AP radiograph were 108.6 mm and 95.8 mm, the mean talo-navicular uncoverage angle was 26.2 and the mean talus-first metatarsal angle was 20.0 degrees. In the control group, the mean medial and lateral column lengths on the AP radiograph were 108.8 mm and 96.5 mm, the mean talo-navicular uncoverage angle was 8.2 and the mean talus-first metatarsal angle was 7.7 degrees. On the lateral radiograph in the flatfoot group, the mean medial and lateral column lengths were 167.2 mm and 166.6 mm, the mean medial and lateral column heights were 16.0 mm and 14.7 mm, the mean calcaneal pitch angle was 15.6 and the talus-first metatarsal angle was 10.3 degrees and for the control group, the mean medial and lateral column lengths were 165.3 mm and 163.5 mm, the mean medial and lateral column heights were 22.8 mm and 13.1 mm, the mean calcaneal pitch angle was 22.4 and the talus-first metatarsal angle was -3.6 degrees. None of the differences in measurements for medial and lateral column lengths between the flatfoot and control groups achieved statistical significance. However, statistically significant differences between the 2 groups were observed in the measurements for medial and lateral column heights, talo-navicular uncoverage angle, calcaneal pitch angle, and talus-first metatarsal angle.CONCLUSION: There is no difference in lateral column lengths between patients with and without adult flatfoot deformity. The perceived shortened lateral column is likely due to forefoot abduction and hindfoot valgus deformities that are associated with adult flatfoot deformity.LEVEL OF EVIDENCE: Level III, comparative series.PMID:
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External link. Please review our .Mapping of QTLs for lateral root branching and length in maize (Zea mays L.) under differential phosphorus supply.
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):688-95. Epub
2005 Jul 15.Mapping of QTLs for lateral root branching and length in maize (Zea mays L.) under differential phosphorus supply.1, , .1Department of Horticulture, Pennsylvania State University, University Park, PA 16802, USA. JPL4@psu.eduAbstractLow phosphorus availability is a primary constraint for plant growth in terrestrial ecosystems. Lateral root initiation and elongation may play an important role in the uptake of immobile nutrients such as phosphorus by increasing soil exploration and phosphorus acquisition. The objective of this study was to identify quantitative trait loci (QTLs) controlling lateral root length (LRL), number (LRN), and plasticity of the primary seedling root of maize under varying phosphorus availability. Using a cigar roll culture in a controlled environment, we evaluated primary root LRL and LRN at low and high phosphorus availability in 160 recombinant inbred lines (RILs) derived from a cross between maize genotypes B73 and Mo17, which have contrasting adaptation to low phosphorus availability in the field. Low phosphorus availability increased LRL by 19% in Mo17, the phosphorus-efficient parent, but significantly decreased LRL in B73, the phosphorus-inefficient genotype. Substantial genetic variation and transgressive segregation for LRL and LRN existed in the population. The plasticity of LRL ranged from -100% to 146.3%, with a mean of 30.4%, and the plasticity of LRN ranged from -82.2% to 164.1%, with a mean of 18.5%. On the basis of composite interval mapping with a LOD threshold of 3.27, one QTL was associated with LRN plasticity, five QTLs were associated with LRL and one QTL was associated with LRN under high fertility. Under low fertility, six QTLs were associated with LRL and one QTL with LRN. No QTLs were detected for plasticity of LRL. A number of RILs exceeded Mo17, the phosphorus-efficient parent, for LRL, LRN, and plasticity. The detection of QTLs for these traits, in combination with the observation of transgressive segregants in our population, indicates that favorable alleles can be combined to increase seedling lateral root growth in maize.PMID:
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