Precursors to regulatory peptides: their proteolytic processing

Isolation and identification of endogenous RFamide-related peptides 1 and 3 in the mouse hypothalamus

Although the RFamide-related peptide (RFRP) preproprotein sequence is known in mice, until now, the molecular structure of the mature, functional peptides processed from the target precursor molecule has not been determined. In the present study, we purified endogenous RFRP1 and RFRP3 peptides from mouse hypothalamic tissue extracts using an immunoaffinity column conjugated with specific antibodies against the mouse C-terminus of RFRP-1 and RFRP-3. Employing liquid chromatography coupled with mass spectrometry, we demonstrated that RFRP1 consists of 15 amino acid residues and RFRP3 consists of 10 amino acid residues (ANKVPHSAANLPLRF-NH2 and SHFPSLPQRF-NH2, respectively). To investigate the distribution of RFRPs in the mouse central nervous system, we performed immunohistochemical staining of the brain sections collected from wild-type and Rfrp knockout animals. These data, together with gene expression in multiple tissues, provide strong confidence that RFRP-immunoreactive neuronal cells are localised in the dorsomedial hypothalamic nucleus (DMH) and between the DMH and the ventromedial hypothalamic nuclei. The identification of RFRP1 and RFRP3 peptides and immunohistochemical visualisation of targeting RFRPs neurones in the mice brain provide the basis for further investigations of the functional biology of RFRPs.

Cysteinyl proteinases and their selective inactivation

The affinity-labeling of cysteinyl proteinases may now be carried out with a number of peptide-derived reagents with selectivity, particularly for reactions carried out in vitro. These reagents have been described with emphasis on their selectivity for cysteine proteinases and lack of action on serine proteinases, the most likely source of side reactions among proteinases. Perhaps a crucial feature of this selectivity is an enzyme-promoted activation due to initial formation of a hemiketal, which may destabilize the reagent. Prominent among the reagent types that have this class selectivity are the peptidyl diazomethyl ketones, the acyloxymethyl ketones, the peptidylmethyl sulfonium salts, and peptidyl oxides analogous to E-64. The need for specific inhibitors capable of inactivating the target enzyme in intact cells and animals is inevitably pushing the biochemical application of these inhibitors into more complex molecular environments where the possibilities of competing reactions are greatly increased. In dealing with the current state and potential developments for the in vivo use of affinity-labeling reagents of cysteine proteinases, the presently known variety of cysteinyl proteinases had to be considered. Therefore this chapter has, at the same time, attempted to survey these proteinases with respect to specificity and gene family. The continual discovery of new proteinases will increase the complexity of this picture. At present the lysosomal cysteine proteinases cathepsins B and L and the cytoplasmic calcium-dependent proteinases are reasonable goals for a fairly complete metabolic clarification. The ability of investigators to inactivate individual members of this family in vivo, possibly without complications due to concurrent inactivation of serine proteinases by improvements in reagent specificity, is increasing. Among the cysteine proteinases, at least those of the papain super family, hydrophobic interactions in the S2 and S3 subsites are important and some specificity has been achieved by taking advantage of topographical differences among members of this group. Some of this has probably involved surface differences removed from the regions involved in proteolytic action. The emerging cysteine proteinases include some which, in contrast to the papain family, have a pronounced specificity in S1 for the binding of basic side chains, familiar in the trypsin family of serine proteinases. At least a potential conflict with serine proteinases can be avoided by choice of a covalent bonding mechanism. The departing group region, has not been exploited. As a sole contributor to binding, this region may be rather limited as a source of specificity.(ABSTRACT TRUNCATED AT 400 WORDS)

Bioinformatic analysis of peptide precursor proteins

Neuropeptides are among the most important signal molecules in animals. Traditional identification of peptide hormones through peptide purification is a tedious and time-consuming process. With the advent of the genome sequencing projects, putative peptide precursor can be mined from the genome. However, because bioactive peptides are usually quite short in length and because the active core of a peptide is often limited to only a few amino acids, using the BLAST search engine to identify neuropeptide precursors in the genome is difficult and sometimes impossible. To overcome these shortcomings, we subject the entire set of all known Drosophila melanogaster peptide precursor sequences to motif-finding algorithms in search of a motif that is common for all prepropeptides and that could be used in the search for new peptide precursors.

Evolution of vertebrate neuropeptides

This review describes some of the most typical features in the evolution of neuropeptides. Neuropeptides are synthesized like other polypeptides and proteins, with an amino acid sequence determined by the DNA sequence of the corresponding gene. Mutations of bases in the coding regions of the DNA lead to changes in amino acid sequence, and explain the differences in amino acid sequence of a certain neuropeptide in different animal species. The more distantly related two species are, the more substitutions can be found in one and the same neuropeptide. The biologically active part of the neuropeptide is usually the most conserved part. Neuropeptides also form families of closely related peptides, where several members may occur in one animal species. This is due to gene or exon duplications followed by mutations. Gene splicing and posttranslational processing decides the gene product in a single cell. Difference in sequence may cause difference in function, but more often than not, members of a family appear to produce the same effect. Three neuropeptide families, the tachykinins, the neuropeptide Y family, and the vasoactive intestinal polypeptide/pituitary adenylate cyclase-activating peptide family will be described in more detail.

Hippocampal cholinergic neurostimulating peptides (HCNP)

Neuronal development and differentiation require a variety of cell interactions. Diffusible molecules from target neurons play an important part in mediating such interactions. Our early studies used explant culture technique to examine the factors that enhance the differentiation of septo-hippocampal cholinergic neurons, and they revealed that several components resident in the hippocampus are involved in the differentiation of presynaptic cholinergic neurons in the medial septal nucleus. One of these components, originally purified from young rat hippocampus, is a novel undecapeptide (hippocampal cholinergic neurostimulating peptide; HCNP); this enhances the production of ChAT, but not of AchE. Later experiments revealed that: (1) a specific receptor appears to mediate this effect; (2) NGF and HCNP act cooperatively to regulate cholinergic phenotype development in the medial septal nucleus in culture; and (3) these two molecules differ both in their mechanism of release from the hippocampus and their mechanism of action on cholinergic neurons. The amino acid sequence deduced from base sequence analysis of cloned HCNP-precursor protein cDNA shows that HCNP is located at the N-terminal domain of its precursor protein. The 21 kDa HCNP precursor protein shows homology with other proteins, and it functions not only as an HCNP precursor, but also as a binding protein for ATP, opioids and phosphatidylethanolamine. The distribution and localization of HCNP-related components and the expression of their mRNAs support the notion that the precursor protein is multifunctional. In keeping with its multiple functions, the multiple enhancers and promoters found in the genomic DNA for HCNP precursor protein may be involved in the regulation of its gene in a variety of cells and at different stages of development. Furthermore, several lines of evidence obtained from studies of humans and animal models suggest that certain types of memory and learning disorders are associated with abnormal accumulation and expression of HCNP analogue peptide and/or its precursor protein mRNA in the hippocampus.

Furin: a mammalian subtilisin/Kex2p-like endoprotease involved in processing of a wide variety of precursor proteins

Limited endoproteolysis of inactive precursor proteins at sites marked by paired or multiple basic amino acids is a widespread process by which biologically active peptides and proteins are produced within the secretory pathway in eukaryotic cells. The identification of a novel family of endoproteases homologous with bacterial subtilisins and yeast Kex2p has accelerated progress in understanding the complex mechanisms underlying the production of the bioactive materials. Seven distinct proprotein convertases of this family (furin, PC2, PC1/PC3, PC4, PACE4, PC5/PC6, LPC/PC7/PC8/SPC7) have been identified in mammalian species, some having isoforms generated via alternative splicing. The family has been shown to be responsible for conversion of precursors of peptide hormones, neuropeptides, and many other proteins into their biologically active forms. Furin, the first proprotein convertase to be identified, has been most extensively studied. It has been shown to be expressed in all tissues and cell lines examined and to be mainly localized in the trans-Golgi network, although some proportion of the furin molecules cycle between this compartment and the cell surface. This endoprotease is capable of cleaving precursors of a wide variety of proteins, including growth factors, serum proteins, including proteases of the blood-clotting and complement systems, matrix metalloproteinases, receptors, viral-envelope glycoproteins and bacterial exotoxins, typically at sites marked by the consensus Arg-Xaa-(Lys/Arg)-Arg sequence. The present review covers the structure and function of mammalian subtilisin/Kex2p-like proprotein convertases, focusing on furin (EC 3.4.21.85).

Seven tachykinin-related peptides isolated from the brain of the Madeira cockroach: evidence for tissue-specific expression of isoforms

We have isolated seven tachykinin-related peptides (TRPs) from an acidic extract of 1000 brains of the cockroach Leucophaea maderae. Four different reversed-phase high performance liquid chromatography (RP-HPLC) column systems were required to obtain pure peptides. During the purification the fractions were monitored in a radioimmunoassay (RIA) with an antiserum to locust TRP locustatachykinin I (LomTK I) and a cockroach hindgut muscle contraction bioassay. The sequences of the seven isolated LomTK immunoreactive and myostimulatory peptides were determined by Edman degradation. Six of these were confirmed by mass spectrometry and chemical synthesis as: APSGFLGVRamide, APAMGFQGVRamide, APAAGFFGMRamide, VPASGFFGMRamide, GPSMGFHGMRamide, and APSMGFQGMRamide. The seventh peptide, APEESPKRAPSGFLGVRamide, was confirmed only by mass spectrometry. These peptides were designated Leucophaea maderae tachykinin-related peptides 1, 2, 5-9 (LemTRP 1, 2, 5-9). Two more peptides were isolated using the same assays: SGLDSLSGATFGGNR and ALFEESTVSAEPR. The first shares the C-terminus FX1GX2R with the Lem TRPs, whereas the second one is not related to the TRPs (none of these peptides were synthesized and thus putative C-terminal amidation was not confirmed). Three of the brain peptides, LemTRP 1, 2, and 5, have previously been isolated from the midgut of L. maderae, whereas the others appear to be brain specific. Because the LemTRPs 3 and 4 appear to be unique for the midgut, we have indications for tissue-specific expression of TRPs. All seven confirmed LemTRPs of the brain are myotropic and induce increases in the amplitude and frequency of spontaneous contractions and tonus of hindgut muscle in L. maderae.

Isolation of five tachykinin-related peptides from the midgut of the cockroach Leucophaea maderae: existence of N-terminally extended isoforms

Using a radioimmunoassay (RIA) with an antiserum to the locust neuropeptide locustatachykinin I (LomTK I) and a cockroach hindgut contraction bioassay as monitors, we isolated 5 tachykinin-related peptides from an acidic extract of 600 midguts of the cockroach Leucophaea maderae. A series of 4 different reversed-phase high performance liquid chromatography (rpHPLC) column systems were required to obtain pure peptides. The sequences of the 5 isolated myostimulatory and LomTK immunoreactive peptides were determined by Edman degradation. Four of these were confirmed by mass spectrometry and chemical synthesis as: APSGFLGVRamide, NGERAPGSKKAPSGFLGTRamide, APAMGFQGVRamide and APSGFMGMRamide. The fifth peptide, APEESPKRAPSGFLGVRamide, was confirmed only by mass spectrometry. These peptides, which were designated Leucophaea tachykinin-related peptides 1-5 (LemTRP 1-5), are structurally related to tachykinin-related peptides previously isolated from a locust, blowfly and mosquito species, but showed a somewhat larger variability in their amino-acid sequence (including the carboxy terminus). The two N-terminally extended forms contain putative cleavage sites (KR and KK, respectively) and such extended tachykinins have not been previously identified in insects. All 5 LemTRPs are myotropic and induce increases in the tonus and frequency of spontaneous contractions of hindgut muscle in L. maderae. The potency of the different synthetic isoforms is very similar; they all have a stimulus threshold concentration of 2.5 x 10(-10) M and an ED50 of about 10(-9) M. The synthetic peptides were tested in RIA and found to cross react to different degrees with the antiserum to LomTK I, but it is likely that in immunocytochemistry performed earlier, all 5 forms were detected in the midgut. It is, however, not clear which isoforms are located in endocrine cells and neural fibers of the midgut, respectively.

Effect of substance P and its precursor alpha-protachykinin on intracellular free calcium concentration in human polymorphonuclear leukocytes

The increase in intracellular free calcium concentration is an important step in signal transduction leading to phagocyte activation. The undecapeptide substance P can influence various functions of human polymorphonuclear leukocytes, including chemotaxis, phagocytosis, and respiratory burst. In this study we investigated the ability of low-concentration (that can occur in vivo) substance P (10(-7) M) and its precursor alpha-protachykinin (3 x 10(-7) M) to increase the intracellular free calcium concentration in human polymorphonuclear leukocytes. Cells isolated from ten healthy donors were incubated with substance P or alpha-protachykinin in 1 mM calcium medium for 5 min and the intracellular free calcium concentration was monitored using the fluorescent calcium indicator Fura-2am. Polymorphonuclear leukocytes from 40% of donors responded to both agonists. The substance P- and alpha-protachykinin-induced increase in intracellular free calcium concentration was 59 +/- 13 nM and 58 +/- 12 nM and the extracellular calcium influx contributed to 87 +/- 8% and 54 +/- 8% of the calcium response, respectively. alpha-Protachykinin released almost all the calcium from intracellular stores, while substance P mobilized only 24 +/- 5% of this calcium pool. Finally, cells that responded to a single challenge with substance P and alpha-protachykinin were able to increase their intracellular free calcium concentration in response to each of three consecutive stimulations with these agonists. This may be an additional mechanism by which substance P and its precursor modify the function of human polymorphonuclear leukocytes.

Demonstration and characterization of hippocampal cholinergic neurostimulating peptide (HCNP) processing enzyme activity in rat hippocampus

Hippocampal cholinergic neurostimulating peptide (HCNP) stimulates cholinergic activity of cultured medial septal nuclei explants. It consists of eleven amino acids that are located at the N-terminal region of its precursor protein. This report concerns the demonstration and characterization of an HCNP processing enzyme that cleaves the bioactive undecapeptide from the precursor. The enzyme was purified from the hippocampus of young Wistar rats. A synthetic deacetylated peptide (peptide(1-26)) consisting of the N-terminal 26 amino acids of the HCNP precursor protein served as substrate. The product of the enzyme reaction was identified and quantitated by HPLC using deacetylated HCNP as standard. The amount of undecapeptide generated was directly proportional to the time of incubation of the enzyme reaction mixture. From molecular sieving chromatography it was estimated that the molecular mass of the enzyme is close to 68 kDa. The HCNP processing enzyme has a pH optimum of 6.0 and a K m of 0.50 mM for peptide(1-26). Preincubation at 56 degrees C causes rapid inactivation of the HCNP processing activity. Enzyme activity is enhanced by EDTA and 1,4-dithiothreitol, and inhibited by antipain, chymostatin and E-64. These findings suggest that the enzyme probably has a thiol group in its active site. This novel enzyme of the hippocampus may represent a valuable tool for further studies on the general protein metabolism in the central nervous system, as well as for elucidating the neurochemical aspects of neurodegenerative disorders.

Processing of mouse proglucagon by recombinant prohormone convertase 1 and immunopurified prohormone convertase 2 in vitro

The mouse tumor cell line alpha TC1-6 was used as a model system to examine the post-translational processing of proglucagon. Determination of the mouse preproglucagon cDNA sequence and comparison with the published sequences of rat and human preproglucagons revealed nucleic acid homologies of 89.1 and 84%, respectively, and amino acid homologies of 94 and 89.4%, respectively. Immunohistochemical analyses with antibodies directed against PC2 and glucagon colocalized both the enzyme and substrate within the same secretory granules. PC1 was also immunolocalized in secretory granules. Cells were metabolically labeled with [3H]tryptophan, and extracts were analyzed by reverse-phase high pressure liquid chromatography. Radioactive peptides with retention times identical to those of synthetic peptide standards were recovered and subjected to peptide mapping to verify their identities. To determine the potential role of PC1 and PC2 in proglucagon processing, 3H-labeled proglucagon was incubated in vitro with recombinant PC1 and/or immunopurified PC2. Both enzymes cleaved proglucagon to yield the major proglucagon fragment, glicentin, and oxyntomodulin, whereas only PC1 released glucagon-like peptide-I from the major proglucagon fragment. Neither PC1 nor PC2 processed glucagon from proglucagon in vitro. These results suggest a potential role for PC1 and/or PC2 in cleaving several of the normal products, excluding glucagon, from the mouse proglucagon precursor.

The sex-peptide

Injection of a peptide of 36 amino acids into virgin Drosophila females changes their reproductive properties drastically: males are rejected and egg laying is increased. The neuronal and physiological properties of the virgin state are replaced by a new pattern of behavior and stimulation of egg production and deposition. Under natural conditions, the peptide is synthesized by the male and transferred into the female during copulation. The sex-peptide, therefore, can be considered as a pheromone. In this review, I shall limit my discussion to Drosophila melanogaster.

Insect neuropeptides: discovery and application in insect management

New approaches to the development of insect control agents have been revealed through the molecular description of neuropeptides, their biogenesis, action, and degradation. Prerequisite to the exploitation of a neuropeptide as a lead to control agent development is a thorough understanding of the biochemistry of the neuropeptide and appreciation of its physiological impact. Reliable bioassays must be coupled with advanced biochemical and molecular genetic technologies to overcome limitations imposed by the typically low endogenous levels of individual neuropeptides. Purification, amino acid sequencing, and gene cloning provide the molecular tools necessary for studies on neuropeptide synthesis, processing, secretion, receptor binding, and inactivation. Each of these areas consists of a number of amino acid sequence-, and enzyme-dependent steps which may be considered as targets for the development of highly specific control agents. These agents will include antagonist and superagonists, peptidomimetics, recombinant peptides delivered through the baculovirus technology, receptor blockers, and enzyme inhibitors.

Molluscan putative prohormone convertases: structural diversity in the central nervous system of Lymnaea stagnalis

In the cerebral ganglia of the central nervous system of the freshwater snail Lymnaea stagnalis many neuropeptides are proteolytically processed from larger prohormones at sites marked by both single and multiple basic amino acids. In the present study we identified cloned cDNA and PCR products corresponding to three putative endoproteases that may be involved in prohormone processing. The cDNA encodes a protein of 653 residues with an overall sequence identity of 60%, 41%, 35%, 40%, and 27% with the recently characterized endoproteases PC2, PC1/3, PC4, furin and Kex2, respectively. The Lymnaea preproconvertase has approximately 80% homology with the catalytic domain, and approximately 40% and approximately 50% with the N- and C-terminal part, respectively, of the vertebrate PC2. Two cloned PCR products, Lfur 1 and Lfur 2, show highest sequence identity to furin. Expression of the LPC2 gene is exclusively in the central nervous system, where two LPC2 transcripts of 3.0 and 4.8 kb were detected.

Synthesis of a gene encoding bovine substance P precursors and its expression in Escherichia coli

Using an efficient Escherichia coli expression system, we have been able to obtain the precursor of substance P, alpha-preprotachykinin (alpha PPT). The alpha PPT protein is produced in E. coli as a fusion to beta-galactosidase, and accumulates in the cytoplasm as insoluble inclusion bodies. We also produced protachykinin (alpha PT), i.e., alpha PPT without a signal peptide. Further purification and characterization of the alpha PPT and alpha PT polypeptides strongly suggest that fully purified products can be obtained using our procedures.

Identification and analysis of the gene encoding human PC2, a prohormone convertase expressed in neuroendocrine tissues

In recent studies we have identified PC2 and PC3, members of a family of serine proteases that are related structurally to subtilisin, and have provided evidence that these are involved in the tissue-specific processing of prohormones and neuropeptides. PC2 is expressed at high levels in the islets of Langerhans, where it participates in the processing of proinsulin to insulin (S.P.S. and D.F.S., unpublished data). To evaluate the regulated expression of the human PC2 (hPC2) gene we have analyzed its structure and characterized its promoter. A map of the gene was constructed by using 11 clones isolated from two human genomic DNA libraries. The gene spans greater than 130 kilobase pairs and consists of 12 exons. Comparison with the structure of the gene encoding human furin, another member of this superfamily, revealed a high degree of conservation of exon-intron junctions. The hPC2 gene was localized to chromosome 20, band p11.2. The 5' flanking region of the hPC2 gene is very G+C-rich and contains six potential Sp1 binding sites but no TATA or CAAT box. Expression of chloramphenicol acetyltransferase reporter fusions containing the putative promoter region was observed to occur in beta TC-3 mouse insulinoma cells but not in HepG2 human hepatoma cells, consistent with the known tissue-specific pattern of expression of the hPC2 gene. Analysis of the level of chloramphenicol acetyltransferase activity with several deletion mutants identified the region from -1100 to -539 from the translation start site as essential for hPC2 promoter activity.

Production and biological activity of hybrid growth hormone-releasing hormone propeptides

Growth hormone-releasing hormone (GHRH), a hypothalamic hormone that stimulates the synthesis and release of growth hormone (GH) from anterior pituitary cells, has been previously produced by synthetic peptide chemistry and recombinant DNA procedures. GHRH is capable of stimulating growth as well as eliciting other anabolic effects on animals and thus may have potential applications in agriculture and human medicine. However, economical production of GHRH by recombinant DNA process has been difficult since GHRH is degraded rapidly by endogenous E. coli proteases. We report here an efficient process to produce hybrid GHRH analogs of higher molecular weight. These hybrid GHRH propeptides (proGHRH) are comprised of an analog of GHRH (44 aa) and the human GHRH carboxy-terminal peptide (33 aa). In E. coli K-12 RV308, the expression levels of the proGHRH analogs were estimated to be 10% of the total cellular protein. An in vitro assay to measure the release of rat growth hormone by GHRH analogs using crude E. coli lysates was also developed. This assay showed that the proGHRH analogs produced in E. coli efficiently stimulated GH release from rat anterior pituitary cells. One proGHRH analog, [alao]-proGHRH, was purified ans shown to efficiently elevate plasma GH levels in wether lambs. Our data indicate that the hybrid proGHRH peptides, unlike other hormone propeptides such as proinsulin, are remarkably bioactive.

The tissue distribution of rat chromogranin A-derived peptides: evidence for differential tissue processing from sequence specific antisera

The distribution of chromogranin A and related peptides in rat tissues was investigated using sequence specific antisera. N- and C-terminal antisera and a presumptive C-terminal rat pancreastatin antiserum immunostained an extensive neuroendocrine cell population throughout the gastro-entero-pancreatic tract, anterior pituitary, thyroid and all adrenomedullary cells. However, mid- to C-terminal antisera immunostained a subpopulation of chromogranin A positive cells. Most notable of these was with the KELTAE antiserum (R635.1) which immunostained discrete clusters of adrenomedullary cells and antiserum A87A which immunostained a subpopulation of cells in the anterior pituitary and throughout the gastrointestinal tract. The present study has demonstrated the widespread occurrence of chromogranin A and related peptides in rat neuroendocrine tissues and provides evidence of tissue and cell specific processing.

Microwave irradiation increases recovery of neuropeptides from brain tissues

The effect of focused high energy microwave treatment (MW) on brain concentrations and molecular forms of substance P, neurokinin A, neuropeptide Y, neurotensin, galanin and calcitonin gene-related peptide was investigated. Groups of rats were treated as follows: 1) MW, storage for 60 min at 22 degrees C, 2) Decapitation, storage for 60 min at 22 degrees C. 3) Decapitation, storage for 60 min at 22 degrees C, MW treatment, 4) MW, decapitation, storage for 2 min at 22 degrees C and 5) Decapitation, storage for 2 min at 22 degrees C. Peptide concentrations were in all instances highest in the MW sacrificed groups. MW increased the concentration of intact peptides by rapid inhibition of peptidase activity and increase in peptide solubility/extractability.

Structure, cell-specific expression, and mating-induced regulation of a Drosophila melanogaster male accessory gland gene

The accessory gland of male insects is a secretory tissue of the genital tract made up of several distinct cell types. It secretes components of the ejaculatory fluid which have an important effect on the postmating behavior of the female. We have examined the sequence, structure, and expression of a gene, mst 316, expressed exclusively in the accessory glands of male Drosophila melanogaster. The mst 316 RNA encodes a small, basic protein of 52 amino acids that exhibits features common to precursors of secreted peptides, including a hydrophobic N-terminus. The tissue-specific expression of the mst 316 gene was studied using an mst 316--lacZ hybrid gene inserted into Drosophila by germ line transformation. The mst 316-lacZ fusion protein is expressed exclusively in the "main" cells of the accessory gland. It is first detected upon eclosion and exhibits a burst of synthesis in the first 3 days of adult life. The synthesis of the fusion protein is stimulated by mating, so that beta-galactosidase activity levels are two- to sixfold higher in males allowed to copulate with females compared to virgin male controls of the same age. The mating-stimulated synthesis of the mst 316-lacZ fusion protein, and by inference of the native gene product, appears to be due at least in part to increased transcript levels.

Substrate phosphorylation can inhibit proteolysis by trypsin-like enzymes

The effect of substrate phosphorylation on the susceptibility to proteolytic cleavage by trypsin-like enzymes was investigated using the model heptapeptide Leu-Arg-Arg-Ala-Ser-Leu-Gly, a peptide representing the endogenous phosphorylation site of pyruvate kinase. Phosphorylation of Ser 5 altered the kinetics of proteolysis by two proteases, trypsin and rat plasma kallikrein, both of which cleaved between Arg 3 and Ala 4. In the case of trypsin, phosphorylation decreased the rate of cleavage 47-fold. In the case of rat plasma kallikrein, phosphorylation decreased proteolysis 13-fold. Phosphorylation resulted in an apparent redirection of the preferential site from Arg 3 to Arg 2. Because sequences analogous to this model peptide are commonly found in exposed domains of globular proteins, and since these regions are susceptible to both phosphorylation and protease attack, the results indicate that substrate phosphorylation may selectively influence protein processing and turnover.

Regulation of epithelial transport in the jejunal mucosa of the guinea pig by neurokinins

This study characterizes the actions of the neurokinins and calcitonin-gene related peptide (CGRP) on electrolyte transport across the mucosa of the guinea pig jejunum in vitro in a modified Ussing chamber. By following changes in short circuit current (Isc) induced by substance P (SP) and neurokinins A & B (NKA & NKB) in the presence and absence of tetrodotoxin (TTX) and atropine, it was established that two distinct neurokinin receptors are involved in the regulation of electrolyte transport. NKA preferentially activates a neuronal receptor since the actions of this neurokinin were inhibited by both TTX and atropine. SP, whose actions were reduced to a lesser extent by TTX and atropine, is considered to activate preferentially a receptor on the epithelial cells. The third neurokinin, NKB, appears to act non-selectively on both the neuronal and epithelial receptors. CGRP, which per se did not affect Isc, markedly potentiated the increases in Isc induced by SP and NKB, and thus acts synergistically with the epithelial neurokinin receptor. These results suggest that two distinct neurokinin receptors (the NK-1 and the NK-2) regulate epithelial transport in the jejunal mucosa of the guinea pig, and furthermore indicate that at least one of the peptides found in enteric nerves (i.e. CGRP) modulates the actions of neurokinins on epithelial cells.

The synthesis and properties of peptidylmethylsulphonium salts with two cationic residues as potential inhibitors of prohormone processing

Peptidylmethylsulphonium salts incorporating consecutive basic residues at the C-terminus of the peptidyl portion such as -Arg-Arg-, -Arg-Lys-, -Lys-Lys- and -Lys-Arg- were synthesized and examined as proteinase inhibitors. Serine proteinases with a specificity directed towards hydrolysis at cationic residues were found to be unaffected by these derivatives. On the other hand, cysteine proteinases, cathepsin B and, in particular, clostripain were readily inactivated by affinity labelling. The reagents thus are of promise for the study of prohormone processing promoted by cysteine proteinases.

Cloning, characterization, and sequence of a porcine cDNA encoding a secreted neuronal and endocrine protein

This report describes the cloning, sequence, and characterization of a cDNA which encodes a protein synthesized in the brain and endocrine tissue, including pituitary, adrenal medulla, and ovary. The deduced 207-amino-acid sequence of the 23-kD protein contains a hydrophobic signal peptide suggesting that it is secreted. Northern blot analysis utilizing the cDNA clone identifies a single RNA of approximately 1400 nucleotides in porcine brain, adrenal medulla, pituitary, and ovary, as well as in human endocrine tumors. Very high levels of RNA were observed in one human pancreatic tumor. Southern blot analysis suggests that sequences homologous to the porcine cDNA are present in human, cow, rat, and salmon DNA, indicating that the gene(s) have been highly conserved during evolution.

A male accessory gland peptide that regulates reproductive behavior of female D. melanogaster

The adult male accessory glands of D. melanogaster synthesize and secrete a peptide that represses female sexual receptivity and stimulates oviposition. Normally, this peptide is transferred to females during copulation; however, the peptide shows the same biological activity after purification and subsequent injection into the abdominal cavity of female virgins. Amino acid sequencing of the purified peptide and oligonucleotide-directed cDNA cloning established that the peptide consists of 36 amino acids. It appears to be synthesized as a precursor with a hydrophobic signal sequence of 19 residues at its N-terminal end. The precursor peptide is encoded by a short mRNA that accumulates exclusively in the male accessory gland. The gene has been localized by in situ hybridization to polytene chromosomes at 70A.