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dc.contributor.authorTeh, Evelyn Mei-lin.en_US
dc.date.accessioned2014-10-21T12:35:53Z
dc.date.available2014-10-21T12:35:53Z
dc.date.issued1999en_US
dc.identifier.otherAAINQ57371en_US
dc.identifier.urihttp://hdl.handle.net/10222/55723
dc.descriptionOne of the many mechanisms by which cholesterol homeostasis is maintained is through the reverse cholesterol transport (RCT) pathway. This pathway transports excess cholesterol from the periphery to the liver for bile acid synthesis and excretion, and maintains high density lipoprotein (HDL) concentration and composition. In humans, the enzyme lecithin: cholesterol acyltransferase (LCAT) and cholesteryl ester transfer protein (CETP) are key components of the RCT pathway. HDL particles play a major role in RCT by acting as the initial acceptors of cholesterol from the peripheral cells. Epidemiological studies have shown an inverse correlation between HDL concentration and premature coronary heart disease (CHD). Hence, genetic defects of the enzymes involved in RCT can greatly affect the composition and concentration of HDL particles.en_US
dc.descriptionLCAT and CETP deficiency syndromes are rare genetic disorders of HDL metabolism. Of particular interest are LCAT deficient patients with severe HDL deficiency who show no signs of premature CHD. In contrast, CETP-deficient patients have elevated HDL cholesterol levels but are not particularly protected from premature CHD. These findings are inconsistent with the general concept that increased HDL cholesterol is a negative risk factor for atherosclerosis. Novel mutations have been characterized in the human CETP and the LCAT genes. CETP mutations are prevalent mainly in Japanese populations. The CETP gene mutation in this study is the first in a Caucasian North American subject; this offers the opportunity to study CETP deficiency i n a different genetic and environmental background. The CETP mutation was identified as a single nucleotide substitution (CGA → TGA) in exon 9 that resulted in the premature truncation of the CETP protein. A novel mutation was also identified in the LCAT gene from a French patient. The lack of LCAT activity is the result of a dinucleotide deletion (TG) in exon 4 of the LCAT gene that leads to the premature truncation of the LCAT protein.en_US
dc.descriptionStructural and functional studies were performed to evaluate the significance of the N-terminal 80 residues of the mature LCAT protein. A rat-human chimera (R80H) containing the first 80 residues of the rat sequence attached to residues 81--416 of human LCAT was constructed and transiently expressed in COS-7 cells. A functional R80H chimeric protein was expressed, showing activity with both rHDL substrates (alpha-LCAT activity) and purified human LDL (beta-LCAT activity). Furthermore, the alpha-LCAT activity was enhanced in the presence of human apoA-I. The beta-LCAT activity also appeared to be enhanced. The 5 amino acid differences between the rat and human LCAT most likely disrupted the region involved in interfacial interaction of the enzyme such that the activity with the different substrates were enhanced. In order to test the hypothesis that the far N-terminus of LCAT may anchor the putative "lid" to the enzyme, sequential N-terminal deletion mutants were constructed. The results showed that the first 10 residues were not essential for secretion but are required for enzymatic function as both the alpha-and beta-LCAT activity were abolished.en_US
dc.descriptionThesis (Ph.D.)--Dalhousie University (Canada), 1999.en_US
dc.languageengen_US
dc.publisherDalhousie Universityen_US
dc.publisheren_US
dc.subjectBiology, Molecular.en_US
dc.subjectChemistry, Biochemistry.en_US
dc.titleMolecular defects and structure/function studies of proteins in reverse cholesterol transport.en_US
dc.typetexten_US
dc.contributor.degreePh.D.en_US
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