Molecular characteristics of lipophorin, the juvenile hormone‐binding protein in the hemolymph of the Colorado potato beetle

Abstract

Lipophorin, the protein that specifically binds juvenile hormone in the hemolymph of the Colorado potato beetle, Leptinotarsa decemlineata, is a high‐density lipoprotein of Mr ∼ 574,000. Lipophorin contains 43% lipid and is composed of two apoproteins: apolipophorin I (Mr ∼ 251,000) and apolipophorin II (Mr ∼ 78,000). Both apoproteins contain mannose residues. Carotenoids make up a substantial part of the lipid fraction. Lipophorin constitutes about 25% of the total hemolymph proteins. Its concentration in the hemolymph (26 μM in 4‐day‐old long‐day and 40 μM in 4‐day‐old short‐day beetles) changes with different physiological conditions concomitant with changes in total protein content. Lipophorin specifically binds 10R‐juvenile hormone III with high affinity. The dissociation constant for 10R‐juvenile hormone III is 12 ± 2 nM. One lipophorin molecule contains one specific juvenile hormone‐binding site. The concentration of binding sites therefore equals that of lipophorin in hemolymph.

Isolation and characterization of a high molecular weight JH‐III transport protein in the hemolymph of locusta migratoria

“…On the other hand, two types of high molecular weight binding proteins exist, both of which are lipoproteins. In the Colorado potato beetle we found that lipophorin, a high-density lipoprotein of M, 5: 600,000, contained the high-affinity (Kd = 12+2 nh4) JH-III-specific binding sites [15]. Lipophorin also seems to function as JH carrier in the hemolymph of the cockroaches P. umericunu [20] and L. maderue (F. Engelmann, unreported data).…”

“…2). Moreover, our polyvalent antiserum 600 did not react with purified LP in the Ouchterlony double-diffusion test, suggesting that the JHBP fraction used for immunization did not contain lipophorin, since insect lipophorins appeared to be highly immunogenic [15]. Other possible contaminants, CP and LHP, contained much less lipid [13,19].…”

“…Its concentration changes periodically with the molting cycles, concomitant with changes in total protein concentration. That the concentrations of JHBP generally follow fluctuations in overall hemolymph concentration was shown also for the Colorado potato beetle in which lipophorin acts as JH carrier [15] and even for Munducu sextu, which contains a low molecular weight JHBP [25]. Although JHBP is a minor protein in the hernolymph, the concentration of JH-I11 binding sites is very high, because every molecule contains six binding sites.…”

Storage proteins are present in the hemolymph from larvae and adults of the Colorado potato beetle

“…Immunological tests were performed on whole hemolymph protein Samples or on purified protein samples after separation by SDS-PAGE and Western blotting of the proteins to Immobilon transfer membranes (Millipore, Bedford, MA), as described before [4]. After the transfer step, unoccupied binding sites of the transfer membrane were blocked by incubating the membranes for 45 min at 37°C in a solution of 5% ( w h ) of skimmed milk powder in PBS (10 mM phosphate (pH 7.4), 0.8% NaC1, 0.02% KC1, and 10 mM NaN3).…”

“…Lipophorin from the Colorado potato beetle was isolated and its molecular composition has been characterized. It functions not only as a lipid transport vehicle, but in this beetle it also transports JH [4]. Thus the functions of vitellogenin and lipophorin are relatively well known.…”