NDLI: High- and low-temperature unfolding of human high-density apolipoprotein A-2.

Content Provider	PubMed Central
Author	Gursky, O. Atkinson, D.
Abstract	Human plasma apolipoprotein A-2 (apoA-2) is the second major protein of the high-density lipoproteins that mediate the transport and metabolism of cholesterol. Using CD spectroscopy and differential scanning calorimetry, we demonstrate that the structure of lipid-free apoA-2 in neutral low-salt solutions is most stable at approximately 25 degrees C and unfolds reversibly both upon heating and cooling from 25 degrees C. High-temperature unfolding of apoA-2, monitored by far-UV CD, extends from 25-85 degrees C with midpoint Th = 56 +/- 2 degrees C and vant Hoff's enthalpy delta H(Th) = 17 +/- 2 kcal/mol that is substantially lower than the expected enthalpy of melting of the alpha-helical structure. This suggests low-cooperativity apoA-2 unfolding. The apparent free energy of apoA-2 stabilization inferred from the CD analysis of the thermal unfolding, delta G(app)(25 degrees) = 0.82 +/- 0.15 kcal/mol, agrees with the value determined from chemical denaturation. Enhanced low-temperature stability of apoA-2 observed upon increase in Na2HPO4 concentration from 0.3 mM to 50 mM or addition of 10% glycerol may be linked to reduced water activity. The close proximity of the heat and cold unfolding transitions, that is consistent with low delta G(app)(25 degrees), indicates that lipid-free apoA-2 has a substantial hydrophobic core but is only marginally stable under near-physiological solvent conditions. This suggests that in vivo apoA-2 transfer is unlikely to proceed via the lipid-free state. Low delta H(Th) and low apparent delta Cp approximately 0.52 kcal/mol.K inferred from the far-UV CD analysis of apoA-2 unfolding, and absence of tertiary packing interactions involving Tyr groups suggested by near-UV CD, are consistent with a molten globular-like state of lipid-free apoA-2.
Related Links	http://dx.doi.org/10.1002/pro.5560050913
Ending Page	1882
Page Count	9
Starting Page	1874
File Format	PDF
ISSN	09618368
e-ISSN	1469896X
Journal	Protein Science : A Publication of the Protein Society
Issue Number	9
Volume Number	5
Language	English
Publisher	Cold Spring Harbor Laboratory Press
Publisher Date	1996-09-01
Access Restriction	Open
Rights Holder	Cold Spring Harbor Laboratory Press
Subject Keyword	Biochemistry Molecular Biology Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Medicine Molecular Biology Biochemistry

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