INVESTIGADORES
TRICERRI Maria Alejandra
artículos
Título:
Arrangement of Apolipoprotein A-I in reconstituted High Density Lipoprotein Discs: an alternative model based on fluorescence resonance energy transfer experiments
Autor/es:
TRICERRI, M. A.; BEHLING AGREE, A; SANCHEZ, S. A.; BRONSKY, J.; JONAS, A.
Revista:
BIOCHEMISTRY
Editorial:
AMER CHEMICAL SOC
Referencias:
Lugar: Washington; Año: 2001 vol. 40 p. 5065 - 5074
ISSN:
0006-2960
Resumen:
The folding and organization of apolipoprotein A-I (apoA-I) in discoidal, high-density
lipoprotein (HDL) complexes with phospholipids are not yet completely resolved. For about 20 years, it
was generally accepted that the amphipathic helices of apoA-I lie parallel to the acyl chains of the
phospholipids (?picket fence? model). However, based on the X-ray crystal structure of a large, lipid-free
fragment of apoA-I, a ?belt model? was recently proposed. In this model, the helices of two antiparallel
apoA-I molecules are extended in a circular arrangement and lie perpendicular to the phospholipid acyl
chains. To obtain conclusive information on the spatial organization of apoA-I in discoidal HDL, we
engineered three separate cysteine mutants of apoA-I (D9C, A124C, A232C) for specific labeling with
the fluorescence probes ALEXA-488 or ALEXA-546 (fluorescein and rhodamine derivatives). The labeled
apoA-I was reconstituted into well-defined HDL complexes containing two molecules of protein and
dipalmitoylphosphatidylcholine, and the complexes were used in three quantitative fluorescence resonance
energy transfer (FRET) experiments to determine the distances between two specific sites in an HDL
particle. Comparison of the distances measured by FRET (4.7-7.8 nm) with those predicted from the
existing models indicated that neither the picket fence nor the belt model can account for the experimental
results; rather, a hairpin folding of each apoA-I monomer with most helices perpendicular to the
phospholipid acyl chains and a random head-to-tail and head-to-head arrangement of the two apoA-I
molecules in the HDL particles are strongly suggested by the distance and lifetime data