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标题：High yield overexpression and characterization of human recombinant proapolipoprotein A-I.
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作者：K A McGuire ; W S Davidson ; A Jonas 等
期刊名称：JLR Papers In Press
印刷版ISSN：0022-2275
电子版ISSN：1539-7262
出版年度：1996
卷号：37
期号：7
页码：1519-1528
语种：English
出版社：American Society for Biochemistry and Molecular Biology
摘要：Human apolipoprotein A-I (apoA-I) is the major protein component of high density lipoproteins (HDL) where it defines the particle structure and stability and functions as the main activator of the enzyme lecithin:cholesterol acyltransferase (LCAT). ApoA-I is expressed in the liver as a preproprotein that is targeted to the endoplasmic reticulum for secretion; in plasma, an unknown protease removes the six amino acid long propeptide. In this study, the cDNA coding the human proapoA-I was cloned into an Escherichia coli vector; the overexpressed protein was purified to 99% homogeneity and was extensively characterized together with mature apoA-I purified from plasma. SDS-PAGE, mass spectrometry, and Edman sequence analysis showed that the initial Met residue needed for translation in E. coli is posttranslationally removed from the N-terminal sequence of the proapoA-I. The structural and functional analyses were carried out on the lipid-free and the lipid-bound proteins. ProapoA-I self associated, interacted with dimyristoyl phosphatidylcholine vesicles, and formed secondary structures very similar to the lipid-free apoA-I. Reconstituted HDL particles made with two initial molar ratios of palmitoyloleoyl phosphatidylcholine/cholesterol/apolipoprotein/Na-cholate had identical particle sizes and distributions when apoA-I or proapoA-I were used. Particles having diameters of 79 A and 98 A, containing two apoA-I or proapoA-I molecules per particle, were isolated and characterized. The particles contained the same amounts of alpha-helical structure, had very similar fluorescence properties, and activated LCAT equally well. We conclude that proapoA-I expressed and purified from E. coli is functionally and structurally indistinguishable from mature apoA-I purified from plasma when analyzed in vitro. Therefore, this recombinant proapoA-I and mutants derived from it will be important sources of protein for analyzing apoA-I structure and function, as well as for studies of proapoA-I processing.