Browsing by Subject "Protein multimerization"

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    Characterization of intrinsically disordered proteins with electrospray ionization mass spectrometry: conformational heterogeneity of alpha-synuclein
    (Wiley, 2010-02-15) Frimpong, Agya K.; Abzalimov, Rinat R.; Uversky, Vladimir N.; Kaltashov, Igor A.; Medicine, School of Medicine
    Conformational heterogeneity of alpha-synuclein was studied with electrospray ionization mass spectrometry by analyzing protein ion charge state distributions, where the extent of multiple charging reflects compactness of the protein conformations in solution. Although alpha-synuclein lacks a single well-defined structure under physiological conditions, it was found to sample four distinct conformational states, ranging from a highly structured one to a random coil. The compact highly structured state of alpha-synuclein is present across the entire range of conditions tested (pH ranging from 2.5 to 10, alcohol content from 0% to 60%), but is particularly abundant in acidic solutions. The only other protein state populated in acidic solutions is a partially folded intermediate state lacking stable tertiary structure. Another, more compact intermediate state is induced by significant amounts of ethanol used as a co-solvent and appears to represent a partially folded conformation with high beta-sheet content. Protein dimerization is observed throughout the entire range of conditions tested, although only acidic solutions favor formation of highly structured dimers of alpha-synuclein. These dimers are likely to present the earliest stages in protein aggregation leading to globular oligomers and, subsequently, protofibrils
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    Different Roles of TM5, TM6, and ECL3 in the Oligomerization and Function of Human ABCG2
    (American Chemical Society, 2012-05) Mo, Wei; Qi, Jing; Zhang, Jian-Ting; Pharmacology and Toxicology, School of Medicine
    ABCG2 is a member of the ATP-binding cassette transporter superfamily, and its overexpression causes multidrug resistance (MDR) in cancer chemotherapy. ABCG2 may also protect cancer stem cells by extruding cytotoxic materials. ABCG2 has previously been shown to exist as a high-order homo-oligomer consisting of possibly 8-12 subunits, and the oligomerization domain was mapped to the C-terminal domain, including TM5, ECL3, and TM6. In this study, we further investigate this domain in detail for the role of each segment in the oligomerization and drug transport function of ABCG2 using domain swapping and site-directed mutagenesis. We found that none of the three segments (TM5, TM6, and ECL3) is essential for the oligomerization activity of ABCG2 and that any one of these three segments in the full-length context is sufficient to support ABCG2 oligomerization. While TM5 plays an important role in the drug transport function of ABCG2, TM6 and ECL3 are replaceable. Thus, each segment in the TM5-ECL3-TM6 domain plays a distinctive role in the oligomerization and function of ABCG2.