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Three antibacterial peptides, named protaetins 1, 2, and 3, were purified and characterized from immunized larval hemolymph of Protaetia brevitarsis, a fruit tree pest in Korea. Also, protaetin 1 was cloned. Acid extraction, gel filtration, preparative acid-urea PAGE, and reversed-phase FPLC were used for purification of peptides. Protaetins 1 and 3 had molecular masses of 7.5 and 12 kDa on Tricine SDS-PAGE, respectively, and the molecular mass of protaetin 2 was 9,283.95 Da as determined by MALDI-TOF mass spectrometry. In an antibacterial assay, protaetins showed antibacterial activities against a panel of Gram-positive and -negative bacteria. For the RT-PCR (reverse transcription polymerase chain reaction) to obtain the complete primary sequence, the primer was designed according to the N-terminal amino acid sequence of protaetin 1. Amino acid sequence homology of protaetin 1 with holotricin 2, an antibacterial peptide from Holotrichia diomphalia, showed 99% identity. Northern blot analysis showed that the protaetin 1 gene was strongly expressed in the fat body after Escherichia coli injection, but not in normal fat body. Also, it was expressed in the gut, but was much weaker after immunization.

To identify and characterize the HDLp (high-density lipophorin) receptor from Galleria mellonella (LpRGm), we used techniques of ligand blotting. This method was, to our knowledge, first used to characterize the lipophorin receptor (LpR) in insects. LpRGm had an approximate molecular weight of 97 kDa under non-reducing conditions and bound the HDLp specifically. The time-course of lipophorin binding to their receptor protein was rapid. The binding of lipophorins to their receptors was saturable with a Kd of 34.33+/-4.67 microg/ml. Although Ca2+ was essentially required in the binding of HDLp to their receptors, interestingly increasing concentration of Ca2+ has shown to have a slight inhibitory effect. EDTA was used here as Ca2+ chelating reagent, because Mg2+ in the binding buffer did not affect the binding of HDLp to their receptors, and inhibited the binding of HDLp and LpRGm absolutely. Suramin (polysulfated polycyclic hydrocarbon), known to inhibit the binding of lipoproteins to their receptors, effectively abolished the binding of HDLp to their receptors. LpRGm showed the stage specific binding activity especially in day 1-3 last instar larval, prepupal, and day 1-3 adult stages.

Lipophorin (LP) was purified from haemolymph in last instar larvae of Hyphantria cunea (Drury) by KBr density gradient ultracentrifugation and gel filtration. LP is composed of Apo-LP I and Apo-LP II with molecular weights of 230 kDa and 80 kDa, respectively.The level of haemolymph LP in early pupae was somewhat greater than in last instar larvae. In males, this LP concentration is maintained throughout pupal development, whereas the level of haemolymph LP decreases in female pupae beginning at day 7, coincident with the onset of vitellogenesis in the fall webworm.In both male and female adults, haemolymph LP concentrations were dramatically increased in comparison to their pre-adult levels. Actually, LP was found in the ovary by irnmunodiffusion, tandem-crossed irnmunoelectrophoresis, and Western blotting. Location of LP in the ovary was also traced by immunogold labelling.Also, LP appeared in small amounts in protein yolk bodies of the ovary at an early stage of vitellogenesis, when nurse cells are bigger than the oocyte, but in greater amounts at those stages when the oocyte is larger than nurse cells-that is, when vitellogenesis is actively taking place. This fact clearly reveals that LP is synthesized by fat body and released into the haemolymph, and then taken up by the growing ovary during vitellogenesis. Also, LP was detected in testes by immunological analysis. Western blotting showed that LP was present in testicular fluid but not in the peritoneal sheath and cysts. To test whether LP is also synthesized in testes, testes and fat body tissues were cultured in vitro, indicating that fat body synthesizes LP but testes do not. The result showed that the haemolymph LP itself is taken up into the testes. o 1994 WiIey-Liss, Inc.

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