Abstract :
[en] Recombinant human apolipoprotein A-I (apo A-I) and three deletion mutants: apo
A-I(delta Leu44-Leu126), apo A-I(delta Glu139-Leu170), and apo A-I(delta
Ala190-Gln243), purified from the periplasmic space of Escherichia coli, were
studied. The rate of turbidity decrease following mixing of apo A-I(delta
Ala190-Gln243) with dimyristoylphosphatidylcholine (DMPC) vesicles at 23 degrees
C was 10-fold lower than that of the other apo A-I proteins, confirming that the
carboxy-terminal region of apo A-I plays a role in rapid lipid binding. The
Stokes radii of reconstituted high-density lipoproteins (rHDL), containing
dipalmitoylphosphatidylcholine and cholesterol, were larger for the three apo A-I
mutants [6.3 nm for apo A-I(delta Leu44-Leu126), 6.1 nm for apo A-I(delta
Glu139-Leu170), and 6.5 nm for apo A-I(delta Ala190-Gln243)] than for intact apo
A-I (5.0 nm). The mutant rHDL all contained 4 apo A-I molecules per particle as
compared to 2 for intact apo A-I. Circular dichroism measurements revealed 8
alpha-helices per apo A-I molecule, 5 per apo A-I(delta Leu44-Leu126), 6 per apo
A-I(delta Glu139-Leu170), and 4 per apo A-I(delta Ala190-Gln243) molecule as
compared to predicted values of 8, 5, 6, and 6 alpha-helices,
respectively.
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