Conformational change of the haemolymph juvenile-hormone-binding protein from Galleria mellonella (L)

Collisional mechanism of ligand release by Bombyxmori JHBP, a member of the TULIP / Takeout family of lipid transporters

Juvenile hormones (JHs) regulate important processes in insects, such as postembryonic development and reproduction. In the hemolymph of Lepidoptera, these lipophilic sesquiterpenic hormones are transported from their site of synthesis to target tissues by high affinity carriers, the juvenile hormone binding proteins (JHBPs). Lepidopteran JHBPs belong to a recently uncovered, yet very ancient family of proteins sharing a common lipid fold (TULIP domain) and involved in shuttling various lipid ligands. One important, but poorly understood aspect of JHs action, is the mechanism of hormone transfer to or through the plasma membranes of target cells. Since many membrane-active peptides and proteins, such as the pore-forming bacterial toxins, are activated by low pH or interaction with phospholipid membranes, we have examined the effect of these factors on JH binding by JHBPs. The affinity of Bombyx mori and Manduca sexta JHBPs for JH III was determined by the DCC assay, equilibrium dialysis, and isothermal titration calorimetry, and found to be greatly reduced at low pH, in agreement with previous observations. Loss of binding was accompanied by changes in fluorescence and near-UV CD spectra, indicating significant changes in protein structure in the environment of aromatic residues. The apparent dissociation rate constant (k_off) of the JHBP-JH III complex was greater at acidic pH, suggesting that low pH favors ligand release by opening of the binding pocket. The affinity of recombinant B. mori JHBP (rBmJHBP) was also decreased in the presence of anionic phospholipid vesicles. Measurements of steady-state fluorescence anisotropy with the lipophilic probe TMA-DPH demonstrated that rBmJHBP specifically interacts with anionic membranes. These results suggest the existence of a collisional mechanism for ligand release that may be important for delivery of JHs to the target cells, and could be relevant to the function of related members of this emerging family of lipid-transport proteins.

Different pattern of Galleria mellonella jhbp gene expression in high five and Sf9 cells

Juvenile hormone binding protein (JHBP) is the key element of the system that transmits hormone signals to target tissues. Recently, we found that the core promoter of the jhbp gene is strongly under the control of the TATA box and the transcription start site. In this report, we have shown that the jhbp promoter contains distal regulatory elements whose functionality clearly depends on the particular cell environment and that the scope of research from one cell line is insufficient to generalize the conclusions of the analysis. Cf1/Usp (where Usp is ultraspiracle protein previously known as Cf1, chorion factor 1) elements suppressed transcription of the reporter gene in the High Five cell line but not in the Sf9 cell line. However, upstream from all three Cf1/Usp elements there is a DNA sequence, containing the Zeste element, which activates jhbp in both systems. We found that juvenile hormone strongly inhibited the activity of the jhbp promoter in the Sf9 cell line, whereas it did not have an effect in the High Five cell line. A second key hormone that controls insect development--20-hydroxyecdysone, was also found to suppress the transcription of jhbp. This is the first report describing how these two hormones affect jhbp gene expression in different cell lines.

Crystal structure of silkworm Bombyx mori JHBP in complex with 2-methyl-2,4-pentanediol: plasticity of JH-binding pocket and ligand-induced conformational change of the second cavity in JHBP

Juvenile hormones (JHs) control a diversity of crucial life events in insects. In Lepidoptera which major agricultural pests belong to, JH signaling is critically controlled by a species-specific high-affinity, low molecular weight JH-binding protein (JHBP) in hemolymph, which transports JH from the site of its synthesis to target tissues. Hence, JHBP is expected to be an excellent target for the development of novel specific insect growth regulators (IGRs) and insecticides. A better understanding of the structural biology of JHBP should pave the way for the structure-based drug design of such compounds. Here, we report the crystal structure of the silkworm Bombyx mori JHBP in complex with two molecules of 2-methyl-2,4-pentanediol (MPD), one molecule (MPD1) bound in the JH-binding pocket while the other (MPD2) in a second cavity. Detailed comparison with the apo-JHBP and JHBP-JH II complex structures previously reported by us led to a number of intriguing findings. First, the JH-binding pocket changes its size in a ligand-dependent manner due to flexibility of the gate α1 helix. Second, MPD1 mimics interactions of the epoxide moiety of JH previously observed in the JHBP-JH complex, and MPD can compete with JH in binding to the JH-binding pocket. We also confirmed that methoprene, which has an MPD-like structure, inhibits the complex formation between JHBP and JH while the unepoxydated JH III (methyl farnesoate) does not. These findings may open the door to the development of novel IGRs targeted against JHBP. Third, binding of MPD to the second cavity of JHBP induces significant conformational changes accompanied with a cavity expansion. This finding, together with MPD2-JHBP interaction mechanism identified in the JHBP-MPD complex, should provide important guidance in the search for the natural ligand of the second cavity.

In silico screening of the juvabione category of juvenile hormone analogues with juvenile hormone binding protein of Galleria mellonella--a docking study

Juvabione, dehydrojuvabione and their aromatic analogues act as juvenile hormone mimics against diverse strains of insect species. Large numbers of modified juvenoids containing the juvabione skeleton, with various structural variations, are synthesized. Some of these compounds exhibit a very high degree of juvenile hormone activity and are presently in use. In this paper we report a comparative molecular docking study of synthesized juvabione, natural juvenile hormone III and synthetic insect growth regulators (fenoxycarb, S-21149, Compound 1, pyriproxyfen) with the juvenile hormone binding protein of Galleria mellonella. The study clearly indicates a higher binding affinity of nitro-substituted juvabione over natural juvenile hormone III and synthetic insect growth regulators such as fenoxycarb and S-21149.

Intramolecular cross-linking in the native JHBP molecule

Juvenile hormone binding protein (JHBP) acts as a shuttle, carrying one of the most crucial hormones for insect development to target tissues. We have found that although the JHBP molecule does not contain tryptophan residues, it exhibits a weak fluorescence maximum near 420nm upon excitation at 315nm. Gel filtration experiments performed in denaturing conditions and ESI-MS analyses excluded the possibility that some low molecular ligand was bound to the protein molecules. Further UV and CD spectroscopy studies, as well as immunoblotting, showed that the unusual JHBP optical properties were due to dityrosine intramolecular cross-linking. These bridges were detected both in native and recombinant protein molecules. We believe that in Galleria mellonella hemolymph the DT generation occurs via ROS-mediated oxidation leading to the formation of cross-linked JHBP monomers. MS analyses of peptides generated after JHBP proteolysis indicated, that the dityrosine bridge occurs between the Y128 and Y130 residues.

N-linked glycosylation of G. mellonella juvenile hormone binding protein - comparison of recombinant mutants expressed in P. pastoris cells with native protein

Juvenile hormone (JH) regulates insect growth and development. JH present in the hemolymph is bound to juvenile hormone binding protein (hJHBP) which protects JH from degradation. In G. mellonella, this protein is glycosylated only at one (Asn(94)) of the two potential N-linked glycosylation sites (Asn(4) and Asn(94)). To investigate the function of glycosylation, each of the two potential glycosylation sites in the rJHBP molecule was examined by site-directed mutagenesis. MS analysis revealed that rJHBP overexpressed in the P. pastoris system may appear in a non-glycosylated as well as in a glycosylated form at both sites. We found that mutation at position Asn(94) reduces the level of protein secretion whereas mutation at the Asn(4) site has no effect on protein secretion. Purified rJHBP and its mutated forms (N4W and N94A) have the same JH binding activities similar to that of hJHBP. However, both mutants devoid of the carbohydrate chain are more susceptible to thermal inactivation. It is concluded that glycosylation of JHBP molecule is important for its thermal stability and secretion although it is not required for JH binding activity.

Insect juvenile hormone binding protein shows ancestral fold present in human lipid-binding proteins

Low molecular weight juvenile hormone binding proteins (JHBPs) are specific carriers of juvenile hormone (JH) in the hemolymph of butterflies and moths. As hormonal signal transmitters, these proteins exert a profound effect on insect development. The crystal structure of JHBP from Galleria mellonella shows an unusual fold consisting of a long alpha-helix wrapped in a highly curved antiparallel beta-sheet. JHBP structurally resembles the folding pattern found in tandem repeats in some mammalian lipid-binding proteins, with similar organization of one cavity and a disulfide bond between the long helix and the beta-sheet. JHBP reveals, therefore, an archetypal fold used by nature for hydrophobic ligand binding. The JHBP molecule possesses two hydrophobic cavities. Several lines of experimental evidence conclusively indicate that JHBP binds JH in only one cavity, close to the N- and C-termini, and that this binding induces a structural change. The second cavity, located at the opposite end of the molecule, could bind another ligand.

Unfolding and refolding of juvenile hormone binding protein

Juvenile hormone (JH) regulates insect development. JH present in the hemolymph is bound to a specific glycoprotein, juvenile hormone binding protein (JHBP), which serves as a carrier to deploy the hormone to target tissues. In this report structural changes of JHBP from Galleria mellonella induced by guanidine hydrochloride have been investigated by a combination of size-exclusion chromatography, protein activity measurements, and spectroscopic methods. Molecules of JHBP change their conformation from a native state via two unstable intermediates to a denatured state. The first intermediate appears in a compact state, because it slightly changes its molecular size and preserves most of the JHBP secondary structure of the native state. Although the second intermediate also preserves a substantial part of the secondary structure, it undergoes a change into a noncompact state changing its Stokes radius from approximately 30 to 39 A. Refolding experiments showed that JHBP molecules recover their full protein structure, as judged from the CD spectrum, fluorescence experiments, and JH binding activity measurements. The free energy of unfolding in the absence of the denaturant, DeltaG(D-N), is calculated to be 4.1 kcal mol(-1).

Positions of disulfide bonds and N-glycosylation site in juvenile hormone binding protein

The juvenile hormone binding protein (JHBP) from Galleria mellonella hemolymph is a glycoprotein composed of 225 amino acid residues. It contains four Cys residues forming two disulfide bridges. In this study, the topography of the disulfide bonds as well as the site of glycan attachment in the JHBP molecule from G. mellonella was determined, using electrospray mass spectrometry. The MS analysis was performed on tryptic digests of JHBP. Our results show that the disulfide bridges link Cys10 and Cys17, and Cys151 and Cys195. Of the two potential N-glycosylation sites in JHBP, Asn4, and Asn94, only Asn94 is glycosylated. This site of glycosylation is also found in the fully biologically active recombinant JHBP expressed in the yeast Pichia pastoris.

Cloning and expression of male-specific protein (MSP) from the hemolymph of greater wax moth, Galleria mellonella L

Male-specific protein (MSP) is a soluble protein that accumulates in high amounts in the hemolymph and other organs of adult male wax moth. The MSP was purified from adult male wax moth by gel filtration and reversed phase column chromatography, and its amino acid sequence was determined. Because of blocked N-terminus, several internal amino acid sequences of MSP were obtained by the in-gel digestion method using trypsin. RT-PCR was conducted using degenerate primers designed from the internal amino acid sequences. 5'-RACE PCR was used to obtain the complete coding region and 5'-UTR sequence. The full length MSP cDNA sequence encodes a 239 amino acid polypeptide with an 18 amino acid signal peptide. The putative mature MSP has a molecular mass of 24,317 Da and an isoelectric point (pI) of 6.00, but shows a molecular mass of 27 kDa on SDS-PAGE. Sequence alignment showed a significant similarity between MSP and juvenile hormone binding proteins (JHBPs) of several lepidopteran species, including G. mellonella.

Overexpression of juvenile hormone binding protein in bacteria and Pichia pastoris

Galleria mellonella juvenile hormone binding protein (JHBP) is a single chain glycoprotein with two disulfide bonds and a molecular mass of 25,880 Da. This report describes the expression of JHBP in bacteria and yeast cells (Pichia pastoris). The expression in bacteria was low and the protein was rapidly degraded upon cell lysis. The expression of His8-tagged rJHBP (His8-rJHBP) in P. pastoris was high and the non-degraded protein was purified to homogeneity with high yield in a one-step immobilized Ni++ affinity chromatography. His8-rJHBP from P. pastoris contains one JH III binding site with KD of 3.7 +/- 1.3x10(-7) M. The results suggest that P. pastoris is the preferred system for expression of His8-rJHBP in non-degraded fully active form.

Cloning and sequence analysis of Galleria mellonella juvenile hormone binding protein--a search for ancestors and relatives

Juvenile hormone binding proteins (JHBPs) serve as specific carriers of juvenile hormone (JH) in insect hemolymph. As shown in this report, Galleria mellonella JHBP is encoded by a cDNA of 1063 nucleotides. The pre-protein consists of 245 amino acids with a 20 amino acid leader sequence. The concentration of the JHBP mRNA reaches a maximum on the third day of the last larval instar, and decreases five-fold towards pupation. Comparison of amino acid sequences of JHBPs from Bombyx mori, Heliothis virescens, Manduca sexta and G. mellonella shows that 57 positions out of 226 are occupied by identical amino acids. A phylogeny tree was constructed from 32 proteins, which function could be associated to JH. It has three major branches: (i) ligand binding domains of nuclear receptors, (ii) JHBPs and JH esterases (JHEs), and (iii) hypothetical proteins found in Drosophila melanogaster genome. Despite the close positioning of JHEs and JHBPs on the tree, which probably arises from the presence of a common JH binding motif, these proteins are unlikely to belong to the same family. Detailed analysis of the secondary structure modeling shows that JHBPs may contain a beta-barrel motif flanked by alpha-helices and thus be evolutionary related to the same superfamily as calycins.

Juvenile hormone binding protein and transferrin from Galleria mellonella share a similar structural motif

It has been previously suggested that juvenile hormone binding protein(s) (JHBP) belongs to a new class of proteins. In the search for other protein(s) that may contain structural motifs similar to those found in JHBP, hemolymph from Galleria mellonella (Lepidoptera) was chromatographed over a Sephadex G-200 column and resulting fractions were subjected to SDS-PAGE, transferred onto nitrocellulose membrane and scanned with a monoclonal antibody, mAb 104, against hemolymph JHBP. Two proteins yielded a positive reaction with mAb 104, one corresponding to JHBP and the second corresponding to a transferrin, as judged from N-terminal amino acid sequencing staining. Transferrin was purified to about 80% homogeneity using a two-step procedure including Sephadex G-200 gel filtration and HPLC MonoQ column chromatography. Panning of a random peptide display library and analysis with immobilized synthetic peptides were applied for finding a common epitope present in JHBP and the transferrin molecule. The postulated epitope motif recognized by mAb 104 in the JHBP sequence is RDTKAVN, and is localized at position 82-88.

UV-difference and CD spectroscopy studies on juvenile hormone binding to its carrier protein

Juvenile hormone binding protein (JHBP) from hemolymph of Galleria mellonella is a single-chain glycoprotein of molecular mass near 25,880 containing no Trp residues. The fourth derivative of the protein absorption spectrum shows the characteristic vibrational components of the phenylalanine spectrum within the range 240-270 nm. At longer wavelengths two main bands 0-0 and 0+800 cm(-1) appear, caused by vibrational levels of electronic transition, pi-->pi*, in the tyrosine residues, with maxima at 279 nm and 286 nm, respectively. Two intersection points of the second derivative absorption band with abscissa at about 288.8 nm and 283 nm were analysed for estimation of the environment polarity of Tyr residues in the JHBP molecule. The results obtained suggest that JHBP contains at least two classes of Tyr residues with very apolar environment, similar to that found in azurine. In the JHBP-JH complex only one class of Tyr residues located in a very apolar environment was found, and a small perturbation of disulphide bridges was deduced from the UV-difference spectrum. Ligand perturbation appears as a minimum at 243 nm of the UV-difference spectrum. Comparison of the circular dichroism (CD) spectra for free JHBP with the CD spectra for the JHBP-JH complex monitored in the far-UV (190-240 nm) region indicates rather small differences in the secondary structure of the protein. Although ligand binding induces distinct changes in the near-UV (250-300 nm) region of the CD spectrum of JHBP, it is apparent where both Tyr and Phe residues contribute.

Purification and characterization of a juvenile hormone binding protein from hemolymph of the silkworm, Bombyx mori

A juvenile hormone binding protein (JHBP) has been isolated from Bombyx mori hemolymph by gel filtration, ion-exchange chromatography, chromatofocusing and hydroxyapatite column chromatography. Gel electrophoresis indicates that the isolated protein is homogeneous in the presence or absence of a denaturing agent. The JHBP in question has a relative molecular mass of 32 kDa, determined by denaturing gel electrophoresis. Chromatofocusing analysis indicated that the JHBP is an acidic protein with pI 4.9. The protein exhibits a dissociation constant of 9.0 x 10(-8) M for JH I, 1.14 x 10(-7) M for JH II and 3.9 x 10(-7) M for JH III, and thus its affinity for JH analogues is in the order of JH I > JH II > JH III. Its amino acid composition indicates that the protein consists of 297 residues of 18 kinds of amino acids. The sequence of the N-terminus of the polypeptide chain was determined for 34 of the first 36 residues: Asp-Gln-Asp-Ala-Leu-Leu- Lys-Pro-?-Lys-Leu-Gly-Asp-Met-Gln-Ser-Leu-Ser-Ser-Ala-Thr-Gln-Gln-Phe-Le u-Glu- Lys-Thr-Ser-Lys-Gly-Ile-Pro-?-Tyr-His-.

Ligand binding by a recombinant insect juvenile hormone binding protein

A cDNA for the hemolymph juvenile hormone binding protein (JHBP) of larval Manduca sexta has been isolated, sequenced, and expressed in an insect cell line. A recombinant baculovirus, containing the JHBP cDNA fused to the p10 promoter of Autographa californica nuclear polyhedrosis virus, was constructed. Insect cells (Sf9) infected with this virus secreted recombinant JHBP (rJHBP) into the medium (> 50 micrograms/mL), and cotranslational removal of an 18 amino acid leader sequence was observed. rJHBP was cross-reactive with an antiserum prepared to the hemolymph JHBP and was specifically labeled by [3H]EHDA, a photoaffinity analog of JH II, demonstrating that rJHBP was an isoform of the previously reported 32-kDa JHBP [Lerro, K. A., & Prestwich, G.D. (1990) J. Biol. Chem. 265, 19800-19806]. rJHBP was purified from insect cell medium to homogeneity by ion-exchange and gel-filtration chromatography. The purified rJHBP had a higher affinity (KD = 11 nM for JH I and KD = 42 nM for JH II) than that reported for crude hemolymph JHBP (KD = 80 nM for JH I). The circular dichroism (CD) spectrum of purified rJHBP indicated 34% alpha-helix and 23% beta-sheet. The CD spectra of rJHBP in the presence and absence of JH II were the same, indicating no change in secondary structure induced by ligand binding. Thus, the rJHBP expressed in insect cells binds JHs and is suitable for structural and functional analysis.