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PubMed2000

Structure of the VAP-peptide (BmACP-6.7) gene in the silkworm, Bombyx mori and a possible regulation of its expression by BmFTZ-F1.

The VAP-peptide (BmACP-6.7) is a hydrophobic peptide localized in adult cuticle of the silkworm, Bombyx mori. We isolated and characterized the VAP-peptide gene as a useful marker gene to analyze molecular mechanisms of terminal differentiation processes in the adult. The gene is composed of two exons interrupted by one intron. The 5' upstream promoter region is shown to bear a nucleotide sequence similar to the cis-element that is recognized and bound by the Bombyx mori FTZ-F1 protein (BmFTZ-F1). Expression of the BmFTZ-F1 gene preceded expression of the VAP-peptide gene and injection of 20-hydroxyecdysone suppressed the expression of both genes. An in vitro binding assay indicated direct interaction of BmFTZ-F1 with the VAP-peptide gene promoter sequence. Therefore, BmFTZ-F1 is proposed to be a possible factor regulating the stage-specific expression of the VAP-peptide gene towards adult life.

Amino Acid Sequence↗
PubMed1995

Insect immunity. The inducible antibacterial peptide diptericin carries two O-glycans necessary for biological activity.

A bacterial challenge of larvae of the dipteran insect Phormia terranovae induces the rapid synthesis of diptericin, an antibacterial polypeptide, previously characterized at the amino acid level and indirectly by cDNA cloning studies. This 82-residue polypeptide consists of an N-terminal proline-rich domain and a central and C-terminal glycine-rich domain. Using liquid chromatography coupled to electrospray ionization-mass spectrometry, we demonstrate here that this molecule is more complex than anticipated and carries two O-substitutions on threonine residues, one in the proline-rich domain (residue 10) and one in the glycine-rich domain (residue 54). These substitutions consist of identical trisaccharides: glucose-->galactose-->N-acetylgalactosamine-->(threonine). Treatment of diptericin with O-glycosidase, which selectively removes the substitutions without altering the polypeptide proper, abolishes the antibacterial activity, indicating that this posttranslational modification is essential for biological activity of the polypeptide. We also show that diptericin is posttranslationally modified by a C-terminal amidation.

Amino Acid Sequence↗
PubMed1995

Protein structure encodes the ligand binding specificity in pheromone binding proteins.

The ligand specificities and binding affinities of three recombinant pheromone binding proteins (PBPs) of two saturniid moths (genus Antheraea) were determined by using a novel binding assay in conjunction with two tritium-labeled constituents of the pheromone blend, [3H]-6E,11Z-hexadecadienyl acetate and [3H]-4E,9Z-tetradecadienyl acetate. The new binding assay, in which nonspecific adsorption to a plastic vessel is suppressed by presaturation of the surface with a 1-alkanol, allows measurement of dissociation constants (KD) for lipophilic ligands for their carrier proteins. The three PBPs showed KD values for [3H]-6E,11Z-16:Ac and [3H]-4E,9Z-14:Ac between 0.6 and 30 microM, as determined by Scatchard analysis. Importantly, two PBPs (Aper-1 and Aper-2) from one species showed opposite binding specificities for these two ligands. Aper-1, like Apol-3, showed 15-fold higher affinity for 6E,11Z-16:Ac than for 4E,9Z-14:Ac, while Aper-2 showed a 3.5-fold preference for binding the shorter chain compound. In addition, for the Apol-3 PBP, displacement of [3H]-6E,11Z-16:Ac binding by other pheromone components or analogs showed a clear trend in relative binding affinity: 6E,11Z-16:Ac > 4E,9Z-14:Ac > 6E,11Z-16:Al approximately 16:Ac > 6E,11Z-16:OH > 4E,9Z-14:OH. These data clearly demonstrate a > 1000-fold range of binding affinities among these very similar structures and unambiguously demonstrate the specificity of the PBP-pheromone interaction. Moreover, this assay offers the potential for determining ligand specificities for odorant binding proteins and other proteins in the vertebrate lipocalin superfamily.

Amino Acid Sequence↗
PubMed2000

The receptor binding conformation of bombyxin is induced by alanine(B15).

Bombyxin is an insect hormone with an insulin-like structure which affects the reduction of stored carbohydrates in the silkworm Bombyx mori. The receptor binding surface of bombyxin includes a trough on the interface between the B chain helix and the N-terminal A chain helix. Alanine(B15) is located on the edge of this feature, whereas the bottom is formed by hydrophobic core residues Ile(A2) and Leu(B14). Replacement of alanine(B15) with bulkier residues produces a negative steric effect on bombyxin receptor binding; alpha-aminobutyric acid reduced the affinity to 6.5%, valine to 1.1%, norvaline to 0.88%, and leucine to 0.05%. CD spectra of these analogues were indistinguishable from each other and identical to that of bombyxin. Changing the backbone structure by replacing alanine with glycine and alpha-aminoisobutyric acid resulted in analogues with activities of 3.7 and 1.4%, respectively, but also a disturbed structure as determined by CD spectroscopy. Replacement of other residues on the periphery of the trough, i.e., arginines at positions B12 and B16, also reduced the level of receptor binding but to a lesser extent than the replacement of alanine(B15). The level of receptor binding for citrulline(B12) bombyxin was 17% and for citrulline(B16) bombyxin was 45%. When it is considered that glycine(A1) is located on the edge of the same trough but across from Ala(B15) and is required for maintenance of the overall structure of bombyxin, it is proposed that the bombyxin receptor binding site forms a contiguous hydrophobic area consisting of residues Ile(A2), Leu(B14), and Ala(B15).

Alanine↗
PubMed1993

Aggregation state of spin-labeled cecropin AD in solution.

A spin-labeled derivative of the ion channel peptide cecropin AD (Fink et al., 1988) was synthesized and used to investigate its aggregation state in water and in the presence of a helix-promoting solvent. A cysteine was introduced at position 33 and spin-labeled using the methanethiosulfonate spin label. In low ionic strength aqueous solution, the peptide is monomeric, and the ESR spectrum indicates a high degree of segmental flexibility at the nitroxide attachment point, consistent with a predominantly random coil conformation. Upon addition of 5-10% (v/v) hexafluoro-2-propanol (HFP), the peptide is induced to aggregate as evidenced by significant motional restriction of the spin label and spin-spin broadening of the ESR lines. At higher concentrations of HFP, the peptide reverts to a monomeric state but retains its folded conformation. Our data suggest that between 5 and 10% HFP the peptide undergoes two structural transitions. The first transition starts at 5% and is very cooperative. Its dependence on ionic strength, temperature, and pH indicates that it involves the interconversion between a random coil and an ordered state stabilized by interpeptide electrostatic and hydrophobic interactions. The second transition, which occurs at 11% v/v HFP, is between the self-associated form and an ordered monomeric form. The analysis of our experimental results demonstrates aggregate formation at 5-10% HFP. This may be relevant to the mechanism of channel formation by cecropins in membranes.

Amino Acid Sequence↗
PubMed1994

Binding and state of aggregation of spin-labeled cecropin AD in phospholipid bilayers: effects of surface charge and fatty acyl chain length.

The binding and state of aggregation of cecropin in large unilamellar vesicles of different surface potential and varying acyl chain length were examined using a Cys-33 spin-labeled derivative of cecropin AD (CAD). Association isotherms of the peptide were measured for vesicles of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) containing 5, 15, and 30 mol % 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylglycerol (POPG). The isotherms display a concentration-dependent positive cooperativity indicating the possible formation of cecropin aggregates in the lipid phase. The critical aqueous concentration for aggregation was dependent on the fraction of POPG, suggesting the involvement of acidic lipids in the formation and stabilization of the putative aggregate. Our data also indicate that cooperativity depends on the state of side-chain ionization of an acidic residue that titrates between pH 7 and 4.4. The binding of spin-labeled Cys-33 CAD was found to be influenced by the acyl chain length of the host lipid. The association isotherm of the peptide for dilaureoyl-sn-glycero-3-phosphatidylcholine vesicles containing 30 mol % dilauroyl-sn-glycero-3-phosphatidylglycerol (DLPG) differed significantly from that in POPC/POPG and could be interpreted in terms of a monomer-monomer partitioning between the aqueous and lipid phases. ESR line-shape analysis was consistent with peptide aggregation in dioleoyl-sn-glycero-3-phosphatidylglycerol vesicles but not in DLPG vesicles.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1994

Mode of action of the antibacterial cecropin B2: a spectrofluorometric study.

Cecropin B2 (CecB) is a 35 amino acid residue, antibacterial peptide that was isolated from the hemolymph and cuticular matrix of the silkworm, Bombyx mori. Synthetic peptides with sequences corresponding to CecB and its truncated analogue, [3-->35]CecB, were synthesized and selectively labeled at their N-terminal amino acids with either 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) or rhodamine fluorescent probes. Utilization of these probes facilitated study of the interaction of cecropin with model phospholipid membranes at a high lipid/peptide molar ratio (approximately 3000:1), permitting investigation of the initial steps involved in this process. The surface partition coefficient of CecB, derived from binding isotherms of the NBD-labeled peptide, was 10-fold higher with acidic phospholipids than with zwitterionic ones, which correlates with the high efficiency of CecB and its analogues in permeating acidic phospholipid vesicles. Furthermore, a direct correlation was found between the antibacterial activity of CecB or its truncated analogues and the ability of their Rho-labeled analogues to interact with bacteria and human red blood cells. We propose that CecB binds phospholipid membranes preferentially as monomers lying on the surface, rather than cooperatively as bundles that form transmembranal pores via a "barrel stave" mechanism. This is based on the following: (i) the linearity of CecB's binding isotherms; (ii) the low energy transfer between membrane-embedded donor and acceptor-labeled CecB, even in the presence of a transmembrane potential; (iii) the surface localization of CecB's N-terminus; (iv) the need for more than 100 peptide molecules per phospholipid vesicle to induce initial ion leakage; and (v) the fact that CecB is a highly positively charged amphipathic alpha-helix, and therefore it is not expected to transverse the membrane as a monomer. We speculate that the non-cooperative binding of the peptides on the outer surface of the bacteria (i.e., no aggregation of CecB monomers) may help them to diffuse efficiently into the inner membrane, which is thought to be the target of antibacterial peptides.

Amino Acid Sequence↗
PubMed1994

Solution structure of PMP-D2, a 35-residue peptide isolated from the insect Locusta migratoria.

The three-dimensional solution structure of PMP-D2, a 35 amino acid peptide isolated from the insect Locusta migratoria, has been determined from two-dimensional 1H NMR spectroscopy data. The structure calculations were performed from 222 NOE-derived interproton distances and 11 dihedral angles calculated from the JHN-H alpha coupling constants, using either a combination of distance geometry and restrained simulated annealing or by restrained simulated annealing alone. PMP-D2 contains three disulfide bridges that have been assigned from NMR data and structure calculations and independently confirmed using chemical and enzymatic methods. The core region of PMP-D2 adopts a compact globular fold, stabilized by hydrophobic interactions, which consists of a short three-stranded antiparallel beta-sheet involving residues 8-11, 15-19, and 25-29. Back-calculation of the NOESY spectra was used to validate the final structures. Analysis of the CD spectra of PMP-D2 under various conditions of ionic strength and in the presence of organic solvents demonstrates the high stability of this molecule. PMP-D2 was recently shown to inhibit Ca2+ currents. This activity is discussed based on the comparison of PMP-D2 three-dimensional structure with the recently established three-dimensional structure of the Ca2+ channel blocker omega-conotoxin GVIA.

Amino Acid Sequence↗
PubMed1982

Synthesis of the antibacterial peptide cecropin A (1-33).

Cecropin A(1-33) was synthesized by an improved stepwise solid-phase method. The synthesis was designed to give high coupling yields and minimal amounts of byproducts. All coupling steps were monitored for completion by a new ninhydrin procedure, and the fully protected peptide-resin was analyzed for deletion peptides by the solid-phase Edman preview technique. Both methods indicated that the average coupling yield was greater than 99.8%. The unpurified peptide mixture resulting from HF cleavage and extraction into 10% acetic acid was analyzed by reverse-phase high-pressure liquid chromatography, and 93% of the total product was shown to be the desired [Trp(For)2]cecropin A(1-33), indicating an average yield per synthetic cycle of 99.8%. Removal of the formyl group at pH 9, followed by ion-exchange chromatography, gave the purified product. Cecropin A(1-33) showed antibacterial activity against both Gram-positive and Gram-negative bacteria. Against Escherichia coli, the activity was only slightly lower than that of the natural 37-residue cecropin A when tested over a 100-fold concentration range; the minimum inhibitory concentration was approximately 1 microM. The formyl derivative was somewhat less effective in killing E. coli than the free 1-33 peptide. The antibacterial activity was discussed in terms of an amphipathic alpha-helix structure and the binding of the peptide to bacterial membranes.

Amino Acid Sequence↗
PubMed1987

Purification of sarcotoxin II, antibacterial proteins of Sarcophaga peregrina (flesh fly) larvae.

Three antibacterial proteins with almost identical primary structures termed sarcotoxin IIA, IIB, and IIC were purified to homogeneity from the hemolymph of third instar larvae of Sarcophaga peregrina. The molecular masses of these proteins were about 24,000. These proteins were found to have common antigenicity, and antibody against sarcotoxin IIA cross-reacted with sarcotoxin IIB and IIC. Radioimmunoassay using this antibody showed that these proteins are induced in the hemolymph in response to injury of the larval body wall.

Amino Acids↗
PubMed1988

Molecular cloning, sequencing, and characterization of cDNA for sarcotoxin IIA, an inducible antibacterial protein of Sarcophaga peregrina (flesh fly).

A cDNA clone for sarcotoxin IIA, an antibacterial protein of Sarcophaga peregrina (flesh fly) larvae [Ando, K., Okada, M., & Natori, S. (1987) Biochemistry 26, 226-230], was isolated and characterized. Sarcotoxin IIA was found to consist of 270 amino acid residues. Northern blot analysis showed that the sarcotoxin IIA gene was activated in response to injury of the body wall of the larvae. The gene was activated for much longer after injection of Escherichia coli into the abdominal cavity of larvae than after injection of saline alone. A common nucleotide sequence for mammalian inflammatory mediator protein cDNAs, TTATTTAT, was found in the 3'-untranslated region of sarcotoxin IIA cDNA, suggesting that this protein plays a role in the inflammatory response of this insect.

Amino Acid Sequence↗
PubMed2003

In vivo structure-activity studies on the dark-color-inducing neurohormone of locusts.

In the 11-residue long dark-color-inducing neurohormone (DCIN = [His7]-corazonin), of locusts, from residue 2 to residue 11, one amino acid at each time was substituted by D-phenylalanine (D-Phe). The dark-color-inducing effect of these peptides was investigated in comparison with unaltered DCIN by a bioassay based on nymphs of a DCIN-deficient albino mutant of the migratory locust, Locusta migratoria. Substitution of any single amino acid by D-Phe always reduced the activity, but did not abolish it completely. Maximum inactivation was obtained after substitution of Gln4, Ser6, or Trp9. The latter two residues are within the partial sequence -Ser-Xxx-Gly-Trp- (Xxx = His in theDCIN) that seems to be important for the dark-color-inducing activity, as found also in another study (Insect Biochem. Mol. Biol.32, 2002, 909). GIn4, however, is outside of this partial sequence.Minimal, although still considerable, inactivation occurred after substitution of Gly8, Phe3, or Asn11, despite the fact that Gly8 is within the -Ser-Xxx-Gly-Trp- partial sequence. In conclusion, no single active core was found, indicating that the whole sequence of the DCIN is necessary to induce maximum darkening effect. No difference was found in the activity of the peptides in which Gly8was substituted by D-Phe or by L-Phe. Therefore the -Ser-Xxx-Gly-Trp- partial sequence does not seem to be stabilized by a type II beta-turn. Nevertheless, existence of another kind of turn that includes this partial sequence is feasible. A single unsuccessful attempt was made to discover an antagonist to the DCIN.

Albinism↗
PubMed1978

Current problems in the control of mosquitoes.

Since the incidence of mosquito-borne disease was drastically reduced by the use of DDT in the 1950s, the problem has again worsened and no single method of eradication seems likely to achieve lasting success. It now seems that the best hope lies in the combination of various methods of chemical control and perhaps genetic control to rid the Third World of its most important disease sector.

Animals↗
PubMed1981

Sequence and specificity of two antibacterial proteins involved in insect immunity.

Immune responses have been described for many different insect species. However, it is generally acknowledged that immune systems must therefore differ from those of vertebrates. An effective humoral immune response has been found in pupae of the cecropia moth, Hyalophora cecropia. The expression of this multicomponent system requires de novo synthesis of RNA and proteins and its broad antibacterial activity is due to at least three independent mechanisms, the most well known of which is the insect lysozyme. However, this enzyme is bactericidal for only a limited number of Gram-positive bacteria. WE recently purified and characterized P9A and P9B, which are two small, basic proteins with potent antibacterial activity against Escherichia coli and several other Gram-negative bacteria. We believe that P9A and P9B plays an important part in the humoral immune responses described previously and that the P9 proteins represent a new class of antibacterial agents for which we propose the name cecropins. We describe here the primary structures of cecropins A and B. We also show that cecropin A is specific for bacteria in contrast to melittin, the main lytic component in bee venom which lyses both bacteria and eukaryotic cells.

Amino Acid Sequence↗
PubMed1993

Involvement of an orthologue of the Drosophila pair-rule gene hairy in segment formation of the short germ-band embryo of Tribolium (Coleoptera)

The segments in long germ-band insect embryos, like Drosophila, are all determined at syncytial blastoderm stage. This is in contrast to short germ-band embryos which show an early determination of only the anterior head segments, whereas the more posterior thoracic and abdominal segments are sequentially added after formation of a primary germ anlage (reviewed in ref. 1). Segment formation in Drosophila involves the pair-rule genes which define double segmental periodicities and which have been considered to represent a special adaptation to the long germ-band type development hairy belongs to the primary pair-rule genes in Drosophila which are directly regulated by the gap genes, such as Krüppel. We have isolated the orthologues of hairy and Krüppel from the flour beetle Tribolium castaneum which has a short germ type development. We show here that hairy is expressed in several stripes at blastoderm stage and later on in two stripes in the growth zone of the developing embryo. Krüppel expression overlaps hairy stripe three and four expression, very similar to Drosophila. This suggests that the segment patterning mechanism that acts in an open blastoderm in Drosophila works in a similar way in the cellularized Tribolium embryo.

Amino Acid Sequence↗
PubMed1995

Growth and differentiation in the Drosophila eye coordinated by hedgehog.

Differentiation of the Drosophila retina is asynchronous: it starts at the posterior margin of the eye imaginal disc and progresses anteriorly over two days. During this time the disc continues to grow, increasing in size by approximately eightfold. An indentation in the epithelium, the morphogenetic furrow, marks the front edge of the differentiation wave. Anterior progression of the furrow is thought to be driven by signals emanating from differentiating photoreceptor cells in the posterior eye disc. A good candidate for such a signal is the product of the hedgehog (hh) gene; it is expressed, and presumably secreted, by differentiating photoreceptors and its function is required for continued furrow movement. Here we show that ectopic expression of hedgehog sets in motion ectopic furrows in the anterior eye disc. In addition to changes in cell shape, these ectopic furrows are associated with a tightly orchestrated series of events, including proliferation, cell cycle synchronization and pattern formation, that parallel normal furrow progression. We propose that the morphogenetic furrow coincides with a transient boundary that coordinates growth and differentiation of the eye disc, and that hedgehog is necessary and sufficient to propagate this boundary across the epithelium.

Animals↗