Tm. Forte et al., STRUCTURAL RELATIONSHIPS BETWEEN NASCENT APOA-I-CONTAINING PARTICLES THAT ARE EXTRACELLULARLY ASSEMBLED IN CELL-CULTURE, Journal of lipid research, 37(5), 1996, pp. 1076-1085
Apolipoprotein A-I (apoA-I) incubated with CHO cells assembles three m
ajor nascent lipid complexes two diameters of 7.3, 9, and 11 nm. Previ
ous studies suggested that the smaller nascent particles were precurso
rs for the larger nascent ones. To test this hypothesis, the 7.3, 9, a
nd 11 nm apoA-I-lipid complexes formed by incubating CHO cells with li
pid-free apoA-I were isolated and subsequently each subpopulation was
re-incubated with cells in the absence of other subpopulations. The ph
ysical-chemical characteristics of each subpopulation were examined be
fore and after re-incubation in an effort to understand relationships;
if any, between the different nascent complexes. The 7.3, 9, and 11 n
m complexes were unique in that each of the particles had pre-alpha mo
bility on agarose gels; this rapid migration was not altered by re-inc
ubation with cells. Protein crosslinking studies indicated that the 7.
3, 9, and 11 nm complexes possessed 2, 3, and 4 apoA-I molecules per c
omplex, respectively; it is unlikely that the size of the particle and
number of apoA-I molecules per particle played a role in the increase
d negative charge of the particles. The present study shows that small
er particles did not give rise to larger ones upon re-incubation with
cells. Rather, the 11 and 9 nm particles both generated smaller discs
(the 11 nm giving rise primarily to 9 nm discs and the 9 nm complex gi
ving rise to 7.3 nm discs) suggesting that, during incubation with cel
ls, the complexes are destabilized and remodeled into smaller, not lar
ger, complexes. Surprisingly, the 7.3 nm complexes during re-incubatio
n with cells were extremely stable and did not undergo size alteration
. When the 7.3 nm particles were incubated with additional small quant
ities of lipid-free apoA-I (1-2 mu g/ml), larger discoidal complexes w
ere generated suggesting that the formation of larger particles may be
driven by the availability of lipid-free apoA-I;-Forte, T. M., J. K.,
Bielicki, L. Knoff, and M. R. McCall. Structural relationships betwee
n nascent apoA-1-containing particles that are extracellularly assembl
ed in cell culture.