Synthesis, radiolabeling and biological activity of peptide oostatic hormone and its analogues

Oostatic peptides

Oostatic peptides are organic molecules, which influence an insect reproduction due to a regulation of the eggs development. It was proved that decapeptide-H-Tyr-Asp-Pro-Ala-Pro-Pro-Pro-Pro-Pro-Pro-OH (YDPAPPPPPP)-isolated from mosquito Aedes aegypti, inhibits trypsin activity in the midgut of the mosquito. Therefore, it was named trypsin-modulating oostatic factor (Aea-TMOF). Feeding the recombinant cells with cloned and expressed TMOF on the coat protein of tobacco mosaic virus (TMV) to mosquito larvae, caused larval mortality. The TMOF was therefore designed for usage as a new biorational insecticide against mosquito. Similarly, a hexapeptide-H-Asn-Pro-Thr-Asn-Leu-His-OH (NPTNLH)-was isolated from the grey flesh fly Neobellieria bullata. This peptide and some of its analogs inhibited trypsin-like synthesis by the midgut in female flies and was therefore entitled Neb-TMOF. Interestingly, the synthetic Aea-TMOF and mainly its C-terminus shorten analogs, including those containing D-amino acids or methylene-oxy isosteric bond, quickly and strongly inhibited the hatchability and egg development in the flesh fly N. bullata.

Oostatic peptides containing D-amino acids: synthesis, oostatic activity, degradation, accumulation in ovaries and NMR study

Analogs of the H-Tyr-Asp-Pro-Ala-Pro-OH pentapeptide with D-amino acid residues either in differing or in all of the positions of the sequences were prepared and their oostatic potency was compared with that of the parent pentapeptide. The D-amino acid residue containing analogs exhibited an equal or even higher oostatic effect in the flesh fly Neobellieria bullata than the parent peptide. Contrary to the rapid incorporation of radioactivity from the labeled H-Tyr-Asp-[3H]Pro-Ala-Pro-OH pentapeptide into the ovaries of N. bullata in vitro, the radioactivity incorporation from the labeled pentapeptides with either D-aspartic acid or D-alanine was significantly delayed. As compared to the parent pentapeptide, also the degradation of both the D-amino acid-containing analogs mentioned above proceeded at a significantly lower rate. The decreased intake of radioactivity, the lower degradation and finally also the high oostatic effect may be ascribed to the decreased enzymatic degradation of the peptide bonds neighboring the D-amino acid residues in the corresponding peptides. The introduction of the non-coded D: -amino acids thus enhances the oostatic effect in N. bullata owing to the prolonged half-life of the corresponding pentapeptides, which can thus affect more ovarian cells.

Study of oostatic peptide uptake and metabolism in developing ovaries of the flesh fly, Neobellieria bullata

The uptake and metabolism of the oostatic pentapeptide analogue of trypsin modulating oostatic factor (TMOF), H-Tyr-Asp-Pro-Ala-Pro-OH (5P), in ovaries of Neobellieria bullata (Parker) (Diptera: Sarcophagidae) were analyzed during their developmental stages. During selected stages of yolk deposition, the fate of [3HPro(3)]5P after its in vivo injection was compared to its uptake after in vitro incubation of dissected ovaries. The ovaries were analyzed from 30 s to 180 min after incubation. A detection sensitivity of 60-100 fmol of the labeled 5P was achieved using radio-high performance liquid chromatography. While the uptake of the applied radioactivity strongly depended on the stage of vitellogenesis, especially for the in vitro experiment, degradation of 5P was very quick and independent of whether the label was injected or incubated with the ovaries, regardless of the developmental stage of ovaries. No tracers of 5P were detected at 30 s after applying the labeled 5P in all tests.

Insect gonadotropic peptide hormones: some recent developments

Gonadotropic peptides are a new generation of peptide hormone regulators of insect reproduction. They have been isolated from ovaries, oviducts, or brains of insects. The subject of this paper is insect peptides that exert stimulatory or inhibitory effects on ovarian development and oocyte maturation. On the basis of the literature data and the results of our investigations, the structure and biological properties of different groups of peptides are presented.

CEC separation of insect oostatic peptides using a strong-cation-exchange stationary phase

The separation of several insect oostatic peptides (IOPs) was achieved by using CEC with a strong-cation-exchange (SCX) stationary phase in the fused-silica capillary column of 75 microm id. The effect of organic modifier, ionic strength, buffer pH, applied voltage, and temperature on peptides' resolution was evaluated. Baseline separation of the studied IOPs was achieved using a mobile phase containing 100 mM pH 2.3 sodium phosphate buffer/water/ACN (10:20:70 v/v/v). In order to reduce the analysis time, experiments were performed in the short side mode where the stationary phase was packed for 7 cm only. The selection of the experimental parameters strongly influenced the retention time, resolution, and retention factor. An acidic pH was selected in order to positively charge the analyzed peptides, the pI's of which are about 3 in water buffer solutions. A good selectivity and resolution was achieved at pH <2.8; at higher pH the three parameters decreased due to reduced or even zero charge of peptides. The increase in the ionic strength of the buffer present in the mobile phase caused a decrease in retention factor for all the studied compounds due to the decreased interaction between analytes and stationary phase. Raising the ACN concentration in the mobile phase in the range 40-80% v/v caused an increase in both retention factor, retention time, and resolution due to the hydrophilic interactions of IOPs with free silanols and sulfonic groups of the stationary phase.

Preparation of tritiated oostatic peptides for study of radioactivity incorporation in flesh fly Neobellieria bullata

A series of insect oostatic peptides containing 3,4-dehydroproline in the C-terminal part or inside of the peptide chain was synthesized and tritiated by addition of (3)H2 to double bond of 3,4-dehydroproline residue. (3)H-label was introduced also into tyrosine residue of oostatic tetra- and pentapeptides by isotopic exchange of benzyl beta-hydrogens. In this way, three types of tritiated peptides were prepared, different in the radiolabeled amino acid position: [(3)H] Tyr-Asp-Pro-Ala-OH, H-Tyr-Asp-[(3)H] Pro-Ala-OH, [(3)H] Tyr-Asp-Pro-Ala-Pro-OH, H-Tyr-Asp-[(3)H] Pro-Ala-Pro-OH, H-Tyr-Asp-Pro-Ala-[(3)H] Pro-OH, H-Tyr-Asp-Pro-Ala-Pro(5)-[(3)H] Pro-OH and H-Asp-[(3)H] Pro-OH. These peptides made possible a highly sensitive comparative study on radioactivity incorporation into head and ovaries of the flesh fly Neobellieria bullata, which revealed this process to proceed differently. The reasons of the found differences are discussed.

Activity and mechanism of action of insect oostatic peptides in flesh fly

The relationship between structure and activity of insect oostatic decapeptide (Aed-TMOF) analogues in flesh fly was analyzed. The highest oostatic activity was exhibited by the pentapetide and tetrapeptide analogues, H-Tyr-Asp-Pro-Ala-Pro-OH and H-Tyr-Asp-Pro-Ala-OH, respectively. The tetrapeptide, either native or tritiated, was used to study its metabolism in the ovaries and hemolymph and to detect putative binding sites in the flesh fly ovaries and head. A high metabolism of the tetrapeptide with a half-life in the hemolymph and ovaries less than 1h was determined. The initial limiting step in the degradation is tyrosine(1) cleavage. Other degradation products were detected only transiently in low quantities. Using tritiated tetrapeptide, we found that only very low specific binding was detected in the homogenates of ovaries and in the rough membrane preparation in the presence and absence of protease inhibitors.

Circular Dichroism and Conformation of Oostatic Peptides: The Carrier-Like Role of C-Terminal Oligoproline Sequence

Circular dichroism spectra of the peptides H-Tyr-Asp-Pro-OH, H-Tyr-Asp-Pro-Ala-OH, H-Tyr-Asp-Pro-Ala-(Pro)n-OH (n = 1-6) and of their two methyleneoxy isosters were measured and analyzed in terms of possible interactions between the N-terminal (mostly tetrapeptide) part that is responsible for the oostatic activity and the C-terminal oligoproline sequence. The results indicate that the two parts are largely independent and that the C-terminal (Pro)n sequence serves another purpose, possibly as a carrier.

Insect oostatic peptide: absence of effect on mice ovaries

An analogue of insect oostatic peptide, the pentapeptide H-Tyr-Asp-Pro-Ala-Pro-OH (H-YDPAP-OH), was administered to female mice and its effects on reproduction and development of the ovaries were studied. Up to 0.5 mg of the peptide per mice (25 g b.w.) injected intraperitoneally did not change the rate of pregnancy, number of offsprings and histological findings in ovaries and uterus in comparison to saline treated controls.

Synthesis and effect of shortened oostatic decapeptide (TMOF) analogs with isosteric structures on reproduction of Neobellieria bullata

Oligopeptides 2a-2d derived from the oostatic decapeptide (TMOF) sequence, H-Tyr-Asp-Pro-Ala-Pro-Pro-Pro-Pro-Pro-Pro-OH (1a) and containing isosteric structures were synthesized and assayed to determine their effect during reproduction in the flesh fly Neobellieria bullata. The N-terminal linear tetra- and pentapeptides 2a, 2b containing the Pro-psi[CH2O]Ala isosteric linkage affect egg development in 80-90% of ovarioles resulting in some resorbed egg chambers, abnormal yolk deposition, the formation of large eggs with irregular yolk granules and proliferation of follicular epithelium. In comparison with their nonisosteric precursors 1b, 1c they exhibit even more accelerated oostatic activity. However, peptides 2c, 2d containing a Pro-psi[CH2S]Ala isosteric linkage are less active.