J. Huuskonen et al., Structure and phospholipid transfer activity of human PLTP: analysis by molecular modeling and site-directed mutagenesis, J LIPID RES, 40(6), 1999, pp. 1123-1130
The plasma phospholipid transfer protein (PLTP) is an important regulator o
f high density lipoprotein (HDL) metabolism. We have here, based on sequenc
e alignments of the plasma LPS-binding/lipid transfer protein family and th
e X-ray structure of the bactericidal/permeability increasing protein (BPI)
, modeled the structure of PLTP, The model predicts a two-domain architectu
re with conserved lipid-binding pockets consisting of apolar residues in ea
ch domain, By site-directed mutagenesis of selected amino acid residues and
transient expression of the protein variants in HeLa cells, the pockets ar
e shown to be essential for PLTP-mediated phospholipid transfer. A solid ph
ase ligand binding assay was used to determine the HDL-binding ability of t
he mutants,j/r The results suggest that the observed decreases in phospholi
pid transfer activity of the N-terminal pocket mutants cannot be attributed
to altered HDL- binding, but the C-terminal lipid-binding pocket may be in
volved in the association of PLTP with HDL, Further, the essential structur
al role of a disulfide bridge between cysteine residues 146 and 185 is demo
nstrated. The structural model and the mutants characterized here provide p
owerful tools for the detailed analysis of the mechanisms of PLTP function,
, Structure and phospholipid transfer activity of human PLTP: analysis by m
olecular modeling and site-directed mutagenesis.