Recombinant proapoA-I(Lys107del) shows impaired lipid binding associated with reduced binding to plasma high density lipoprotein

In the present study apoA-I (Lys 107del), a naturally occurring human apoA- I variant with a deletion of Lys 107, was expressed in E. coli to examine t he effect of this mutation on lipid binding, cholesterol efflux and lecithi n:cholesterol acyltranferase (LCAT) activation. Dimyristoyl phosphatidylcho line (DMPC) binding studies revealed slow interaction of proapoA-I(Lys107de l) with DMPC relative to normal proapoA-I. After preincubation with human p lasma lipoprotein (d < 1.225 g/ml) for I h at 37 degreesC, I-125-labeled no rmal proapoA-I chromatographed as a single peak with the high density lipop rotein (HDL) fraction, whereas I-125-labeled proapoA-I(Lys107del) chromatog raphed with both HDL and free proapoA-I (26% of the radioactivity). Circula r dichroism measurements showed that the a-helical content of lipid-bound p roapoA-I (Lys107del) was reduced to 64 versus 73% of normal proapoA-I. Non- denaturing gradient gel electrophoresis of reconstituted HDL assembled with either proapoA-I(Lys107del) or normal proapoA-I showed that the mutation l ed to the formation of a second population of smaller rHDL particles. DMPC/ proapoA-I(Lys107del) and normal DMPC/proapoA-I complexes exhibited a simila r capacity to promote cholesterol efflux from fibroblasts. ProapoA-I (Lys10 7del) also activated LCAT similar to wild type proapoA-I and human plasma a poA-I. We conclude that deletion of Lys 107 substantially alters the lipid binding properties of the protein, which correlated with reduced binding to plasma HDL in vitro, but did not affect the capacity of the mutant/lipid c omplex to promote cholesterol efflux or activate LCAT. (C) 2001 Elsevier Sc ience Ireland Ltd. All rights reserved.