Different isoforms of an apoprotein (apolipophorin III) associate with lipoproteins in Locusta migratoria.
Insects transport lipid for flight in the form of diacylglycerol-rich low-density lipoproteins (low-density lipophorin, LDLp), which in the hemolymph are produced from high-density lipophorin (HDLp) by reversible association with several molecules of an apolipoprotein, apolipophorin III (apoLp-III, Mr approximately 18,000-20,000) during lipid loading. Two isoforms of apoLp-III (a and b) were purified both from adult Locusta migratoria migratorioides hemolymph and LDLp, which have identical apparent Mr but differ in amino acid composition, NH2-terminal amino acid sequence, and isoelectric points (5.35 +/- 0.01 for apoLp-IIIa, 5.10 +/- 0.01 for apoLp-IIIb). The NH2-terminal sequence of apoLp-IIIb is identical to the primary structure of apoLp-III deduced from cloned cDNA [Kanost et al. (1988) J. Biol. Chem. 263, 10,568-10,573], whereas the NH2-terminal sequence of apoLp-IIIa is identical to that of apoLp-IIIb but preceded by Arg-Pro-, which is the C-terminal of the putative signal peptide coded by cDNA upstream from that coding for apoLp-IIIb. The ratio apoLp-IIIa apoLp-IIIb free in hemolymph is identical to that in LDLp (5:9); since 14 molecules of apoLp-III appear to be bound in one molecule of LDLp, an average of 5 molecules of apoLp-IIIa and 9 of apoLp-IIIb are involved in formation of each LDLp particle. In vivo studies using 35S-labeled apoLp-IIIa and b demonstrate that each of the isoforms can associate with HDLp to produce LDLp reversibly; in an in vitro system, production of LDLp containing exclusively apoLp-IIIa or apoLp-IIIb demonstrates independent participation of each isoform in LDLp formation.
Van der Horst
D J
DJ
Department of Experimental Zoology, University of Utrecht, The Netherlands.
Van Doorn
J M
JM
Voshol
H
H
Kanost
M R
MR
Ziegler
R
R
Beenakkers
A M
AM
D000595:Amino Acid Sequence; D000818:Animals; D001053:Apolipoproteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D006110:Grasshoppers; D006458:Hemolymph / Q000378:metabolism; D007526:Isoelectric Point; D008077:Lipoproteins, LDL / Q000378:metabolism*; D008297:Male; D008969:Molecular Sequence Data; D012689:Sequence Homology, Nucleic Acid
D001053:Apolipoproteins; D008077:Lipoproteins, LDL; C042470:apolipophorin III