Molecular characterization of quail apolipoprotein very-low-density lipoprotein II: disulphide-bond-mediated dimerization is not essential for inhibition of lipoprotein lipase.
As part of the avian reproductive effort, large quantities of triglyceride-rich very-low-density lipoprotein (VLDL) particles are transported by receptor-mediated endocytosis into the female germ cells. Although the oocytes are surrounded by a layer of granulosa cells harbouring high levels of active lipoprotein lipase, non-lipolysed VLDL is transported into the yolk. This is because VLDL particles from laying chickens are protected from lipolysis by apolipoprotein (apo)-VLDL-II, a potent dimeric lipoprotein lipase inhibitor [Schneider, Carroll, Severson and Nimpf (1990) J. Lipid Res. 31, 507-513]. To determine whether this protection depends on dimer formation and constitutes a general mechanism to ensure high levels of yolk triglycerides for embryonic utilization in birds, we have now molecularly characterized apo-VLDL-II in the Japanese quail, a frequently used avian species. Quail apo-VLDL-II shows 72% amino acid identity with the chicken protein, with most replacements being in the C-terminal region. Importantly, quail apo-VLDL-II lacks the single cysteine residue present eight residues from the C-terminus of chicken apo-VLDL-II, which is responsible for dimerization of the chicken lipoprotein lipase inhibitor. Nevertheless, monomeric quail and dimeric chicken apo-VLDL-II display, on a molar basis, identical inhibitory effects on lipoprotein lipase, underscoring the biological importance of their function. Furthermore secondary structure prediction of the 3'-untranslated region of the quail message supports a role for loop structures in the strictly oestrogen-dependent production of the lipoprotein lipase inhibitors. Our findings shed new light on the essential role of this small, hormonally regulated, protein in avian reproduction.
MacLachlan
I
I
Department of Molecular Genetics, Biocenter, Austria.
Steyrer
E
E
Hermetter
A
A
Nimpf
J
J
Schneider
W J
WJ
D000595:Amino Acid Sequence; D000818:Animals; D001053:Apolipoproteins / Q000235:genetics* / Q000494:pharmacology; D001483:Base Sequence; D002645:Chickens / Q000235:genetics; D003370:Coturnix / Q000235:genetics*; D018076:DNA, Complementary; D004220:Disulfides; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D008071:Lipoprotein Lipase / Q000037:antagonists & inhibitors*; D008079:Lipoproteins, VLDL / Q000737:chemistry / Q000235:genetics* / Q000494:pharmacology / Q000648:ultrastructure; D008297:Male; D008969:Molecular Sequence Data; D010058:Oviposition; D010063:Ovum / Q000254:growth & development; D016133:Polymerase Chain Reaction; D011487:Protein Conformation; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity
D001053:Apolipoproteins; D018076:DNA, Complementary; D004220:Disulfides; D004791:Enzyme Inhibitors; D008079:Lipoproteins, VLDL; C027610:apolipoprotein VLDL II; D008071:Lipoprotein Lipase