F. Emmanuel et al., IDENTIFICATION OF SPECIFIC AMPHIPATHIC ALPHA-HELICAL SEQUENCE OF HUMAN APOLIPOPROTEIN A-IV INVOLVED IN LECITHIN-CHOLESTEROL ACYLTRANSFERASEACTIVATION, The Journal of biological chemistry, 269(47), 1994, pp. 29883-29890
To investigate the structure-function relationship of human apolipopro
tein A-IV (apoA-IV), several deletion mutants of this protein were con
structed by sequentially removing pairs of ga-residue repeats, potenti
ally having an amphipathic cu-helical conformation. The mutants, produ
ced as recombinant poly-histidine tagged apolipoproteins (t-apo) in Es
cherichia coli, assembled with phosphatidylcholine (i.e. dimyristoylph
osphatidylcholine, palmitoyloleoylphosphatidylcholine, or egg lecithin
) as did native apoA-IV. Lecithin:cholesterol acyltransferase (LCAT) c
ofactor function, measured as cholesterol esterification occurring whe
n t-apo-phosphatidylcholine-cholesterol complexes were incubated with
purified enzyme, decreased significantly when pairs of repeats between
residues 117 and 248 were deleted and most markedly when residues 117
-160 were deleted. LCAT cofactor activity decreased by 90 and 75%, res
pectively, when egg lecithin or palmitoyloleoylphosphatidylcholine was
used to form the particles with the Delta aa 117-160 mutant, Thus, on
the basis of deletion scanning of t-apo, residues 117-160 seem to be
involved in the LCAT cofactor function of apoA-IV.