Cholesterol's role in the molecular architecture of polyunsaturated model membranes

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Ab initio molecular-replacement phasing for symmetric helical membrane proteins

An ab initio molecular-replacement method for phasing X-ray diffraction data for symmetric helical membrane proteins has been developed. The described method is based on generating all possible orientations of idealized transmembrane helices and using each model in a molecular-replacement search

Molecular organization of cholesterol in polyunsaturated membranes: microdomain formation.

The molecular organization of cholesterol in phospholipid bilayers composed of 1,2-diarachidonylphosphatidylcholine (20:4-20:4PC), 1-stearoyl-2-arachidonylphosphatidylcholine (18:0-20:4PC), and 20:4-20:4PC/18:0-20:4PC (1/1 mol) was investigated by solid-state (2)H NMR and by low- and wide-angle x-ray diffraction (XRD). On the basis of distinct quadrupolar powder patterns arising from [3 alpha-(2)H(1)]cholesterol intercalated into the membrane and phase separated as solid, solubility chi(NMR)(chol) = 17 +/- 2 mol% and tilt angle alpha(0) = 25 +/- 1 degrees in 20:4-20:4PC were determined. The corresponding values in 18:0-20:4PC were chi (NMR)(chol) > or = 50 mol% and alpha(0) = 16 +/- 1 degrees. Cholesterol solubility determined by XRD was chi(NMR)(chol) = 15 +/- 2 mol% and chi(NMR)(chol) = 49 +/- 1 mol% for 20:4-20:4PC and 18:0-20:4PC, respectively. XRD experiments show that the solid sterol is monohydrate crystals presumably residing outside the bilayer. The (2)H NMR spectrum for equimolar [3 alpha-(2)H(1)]cholesterol added to mixed 20:4-20:4PC/18:0-20:4PC (1/1 mol) membranes is consistent with segregation of cholesterol into 20:4-20:4PC and 18:0-20:4PC microdomains of <160 A in size that preserve the molecular organization of sterol in the individual phospholipid constituents. Our results demonstrate unambiguously that cholesterol has low affinity to polyunsaturated fatty acids and support hypotheses of lateral phase separation of membrane constituents into sterol-poor/polyunsaturated fatty acid-rich and sterol-rich/saturated fatty acid-rich microdomains

Evaluation of a susceptibility gene for schizophrenia: Genotype based meta-analysis of RGS4 polymorphisms from thirteen independent samples

Background: Associations between schizophrenia (scz) and polymorphisms at the regulator of g-protein signaling 4 (rgs4) gene have been reported (single nucleotide polymorphisms [snps] 1, 4, 7, and 18). Yet, similar to other scz candidate genes, studies have been inconsistent with respect to the associated alleles. Methods: In an effort to resolve the role for rgs4 in scz susceptibility, we undertook a genotype-based meta-analysis using both published and unpublished family-based and case-control samples (total n = 13,807). Results: The family-based dataset consisted of 10 samples (2160 families). Significant associations with individual snps/haplotypes were not observed. In contrast, global analysis revealed significant transmission distortion (p = .0009). Specifically, analyses suggested overtransmission of two common haplotypes that account for the vast majority of all haplotypes. Separate analyses of 3486 cases and 3755 control samples (eight samples) detected a significant association with snp 4 (p = .01). Individual haplotype analyses were not significant, but evaluation of test statistics from individual samples suggested significant associations. Conclusions: Our collaborative meta-analysis represents one of the largest scz association studies to date. No individual risk factor arose from our analyses, but interpretation of these results is not straightforward. Our analyses suggest risk due to at least two common haplotypes in the presence of heterogeneity. Similar analysis for other putative susceptibility genes is warranted