PERSONAL DE APOYO
PRIETO Eduardo Daniel
artículos
Título:
Membrane insertion topology of the central apolipoprotein A-I region. Fluorescence studies using single tryptophan mutants
Autor/es:
PRIETO, EDUARDO DANIEL; GARDA, HORACIO ALBERTO
Revista:
BIOCHEMISTRY
Editorial:
AMER CHEMICAL SOC
Referencias:
Año: 2011 vol. 50 p. 466 - 479
ISSN:
0006-2960
Resumen:
Apolipoprotein A-I (apoAI) contains several amphipathic a-helices. To carry out its function, it exchanges between lipid-free and different lipidated states as bound to membranes or to lipoprotein complexes of different morphology, size and composition. When bound to membranes or to spherical lipoprotein surfaces, it is though that most a-helices arranges with their long axis parallel to the membrane surface. However, we previously found that a central region spanning residues 87-112 is exclusively labeled by photoactivable reagents deeply located into the membrane (Córsico et al. 2001, J. Biol. Chem. 276, 16978-16985). A pair of amphipatic a-helical repeats with a particular charge distribution is predicted in this region. In order to study their insertion topology, three single tryptophan mutants, each one containing the tryptophan residue at a selected position in the hydrophobic face of the central Y-helices (W@93, W@104 and W@108), were used. From the accessibility to quenchers located at different membrane depths, distances from the bilayer center of 13.4, 10.5 and 15.7 Å were estimated for positions 93, 104 and 108, respectively. Reported data also indicate that distances between homologous positions (in special for W@93 and W@104) are very short in dimers in aqueous solution, but they are larger in membrane bound dimers. Data indicates that an intermolecular central Y-helix bundle would penetrate the membrane perpendicularly to the membrane surface. Intermolecular helix-helix interactions would occur through the hydrophilic helix faces in the membrane bound bundle, but through the hydrophobic faces in the case of dimers in solution.