Complete amino acid sequence of a VLDV-type neurophysin from ostrich differs markedly from known mammalian neurophysins

Characterization of ostrich (Struthio camelus) beta-microseminoprotein (MSP): identification of homologous sequences in EST databases and analysis of their evolution during speciation

Beta-microseminoprotein, alternatively called prostatic secretory protein of 94 amino acids, is a hydrophilic, unglycosylated, small protein rich in conserved half-cystine residues. Originally found in human seminal plasma and prostatic fluids, its presence was later shown in numerous secretions and its homologs were described in many vertebrate species. These studies showed that this protein had rapidly evolved, but they failed to unambiguously identify its biological role. Here, we show that a protein isolated from ostrich pituitary gland is closely related to a similar one isolated from chicken serum and that the two are structurally related to the mammalian beta-microseminoprotein. The complete 90-amino acid sequence of the ostrich molecule was established through a combination of automated Edman degradation and matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometric procedures, including postsource decay (PSD) and ladder sequencing analyses. This study documents for the first time that beta-microseminoprotein is present in aves. It is also the first report of a C-terminal amidated form for a member of this protein family and the first in which the disulfide linkages are established. Database searches using the herein-described amino acid sequence allowed identification of related proteins in numerous species such as cow, African clawed frog, zebrafish, and Japanese flounder. These small proteins show a strikingly high rate of amino acid substitutions, especially across phyla boundaries. Noticeably, no beta-microseminoprotein-related gene could be found in the recently completed fruit fly genome, indicating that if such a gene exists in arthropods, it must have extensively diverged from the vertebrate ones.

Structure-function relationships of the vasopressin prohormone domains

1. In this review the structure-function relationships of the different vasopressin prohormone domains are dated and discussed, with special reference to the neurophysin and glycopeptide domains. 2. The primary structures of the currently known neurophysins and glycopeptide sequences are compared and discussed. 3. The hormone-binding and aggregational properties of neurophysin are reviewed and related to a possible function within the regulated secretory pathway. 4. It is proposed, based on the properties reviewed here as well as our own data shown here, that the sorting of the vasopressin prohormone is initiated by hormone binding, which triggers aggregation of the prohormone into the characteristic dense cores of the regulated secretory pathway. 5. This may suggest that prohormone sorting into the regulated secretory pathway is, in general, determined by noncovalent, intramolecular interactions that promote aggregation.

Bony fish neurophysins. Identification of MSEL- and VLDV-neurophysins of the pollack (Pollachius virens)

The two types of neurophysins known in vertebrate species, namely MSEL-neurophysin (vasopressin-like hormone-associated neurophysin) and VLDV-neurophysin (oxytocin-like hormone-associated neurophysin) have been purified from the pollack (Pollachius virens) pituitary through a combination of molecular sieving and high-pressure liquid chromatography (HPLC). Homogeneity has been checked by gel electrophoresis and return in HPLC. The apparent molecular masses measured by SDS-electrophoresis are near 12 kDa, significantly higher than those found for their mammalian homologues (10 kDa). The two types of neurophysins have been recognized through their N-terminal amino acid sequences. The primary structure of MSEL-neurophysin has been partially determined using automated Edman degradation applied on native and reduced-alkylated protein, as well as peptides derived by trypsin or staphylococcal proteinase hydrolyses. Comparison of pollack MSEL-neurophysin with ox, goose and frog counterparts reveals that particular positions in the polypeptide chain are subjected to substitutions and that the numbers of substitutions do not seem closely related to the paleontological times of divergence between the different vertebrate classes.

Evolution of the vasopressin/oxytocin superfamily: characterization of a cDNA encoding a vasopressin-related precursor, preproconopressin, from the mollusc Lymnaea stagnalis

Although the nonapeptide hormones vasopressin, oxytocin, and related peptides from vertebrates and some nonapeptides from invertebrates share similarities in amino acid sequence, their evolutionary relationships are not clear. To investigate this issue, we cloned a cDNA encoding a vasopressin-related peptide, Lys-conopressin, produced in the central nervous system of the gastropod mollusc Lymnaea stagnalis. The predicted preproconopressin has the overall architecture of vertebrate preprovasopressin, with a signal peptide, Lys-conopressin, that is flanked at the C terminus by an amidation signal and a pair of basic residues, followed by a neurophysin domain. The Lymnaea neurophysin and the vertebrate neurophysins share high sequence identity, which includes the conservation of all 14 cysteine residues. In addition, the Lymnaea neurophysin possesses unique structural characteristics. It contains a putative N-linked glycosylation site at a position in the vertebrate neurophysins where a strictly conserved tyrosine residue, which plays an essential role in binding of the nonapeptide hormones, is found. The C-terminal copeptin homologous extension of the Lymnaea neurophysin has low sequence identity with the vertebrate counterparts and is probably not cleaved from the prohormone, as are the mammalian copeptins. The conopressin gene is expressed in only a few neurons in both pedal ganglia of the central nervous system. The conopressin transcript is present in two sizes, due to alternative use of polyadenylylation signals. The data presented here demonstrate that the typical organization of the prohormones of the vasopressin/oxytocin superfamily must have been present in the common ancestors of vertebrates and invertebrates.

Animal models for osmoregulatory disturbances

For the various types of di in humans, animal models are available. However, their value for explaining human di is for the major part an indirect one; by studying cellular mechanisms in these animal models, fundamental aspects of the cellular processes become available, which will help to understand similar processes in human di and subsequently lead to the molecular cause(s) of the various types of human di. Finally, it is to be expected that in the very near future transgenic animals will be raised in which very specific genetic information is overexpressed (or knocked out by homologous recombination; McMahon and Bradley, 1990). Recently hypervasopressinemia could be shown in transgenic mice, providing an animal model for the syndrome of the inappropriate VP secretion (Bartter and Schwartz, 1967), which is often observed in patients with lung cancers that ectopically express the VP gene (Habener et al., 1989). Furthermore it will be possible to study the exact cause(s) of human di by performing in vitro mutagenesis and to express the RNA constructs within a cell-free translation system and in oocytes (e.g., Schmale et al., 1989) and subsequently study the pattern of precursor synthesis, packaging and processing.

Purification and primary structure of glucagon from ostrich pancreas splenic lobes

Glucagon is a highly conserved polypeptide hormone which appears to play a more important role in regulation of glycaemia in birds than insulin. Ostrich glucagon was isolated and purified from ostrich pancreas splenic lobes using an adapted acid ethanol extraction procedure, gel filtration, ion exchanges, and HPLC steps. The purified glucagon fraction appeared to contain small quantities of a more acidic contaminant (polyacrylamide gel isoelectric focussing, PAGE) but appeared homogeneous on SDS-PAGE. Amino acid analysis and sequence analysis showed identity with the duck hormone. Identity with the duck hormone was confirmed by liquid phase as well as gas phase sequencing. The ostrich glucagon preparation seemed to have a higher Km than the porcine homologue in stimulating glycerol release from isolated chicken adipocytes.

Complete amino acid sequence of goose VLDV-neurophysin. Traces of a putative gene conversion between promesotocin and provasotocin genes

Goose VLDV-neurophysin (mesotocin-associated neurophysin) has been purified from posterior pituitary glands through molecular sieving on Sephadex G-75 and high-pressure reverse-phase liquid chromatography on Nucleosil C-18 columns. Despite apparent molecular mass of unreduced VLDV-neurophysin measured by polyacrylamide gel electrophoresis with sodium dodecylsulfate appeared near 17 kDa, this value fell to 11 kDa after reduction with mercaptoethanol, suggesting the existence of a homodimer. Complete amino acid sequence (93 residues) of goose VLDV-neurophysin has been determined. N- and C-terminal sequences of the protein have been established by Edman degradation (microsequencing) and use of carboxypeptidase Y, respectively. Peptides derived from oxidized or carboxamidomethylated neurophysin by trypsin or staphylococcal proteinase hydrolyses have been isolated by high-pressure liquid chromatography and microsequenced, allowing determination of the complete sequence. Comparison within the vertebrate VLDV-neurophysin lineage, namely goose VLDV-neurophysin to mammalian VLDV-neurophysins and to deduced toad VLDV-neurophysin, reveals a residue insertion between positions 66 and 67 in the nonmammalian VLDV-neurophysins. When goose MSEL-neurophysin (vasotocin-associated neurophysin) and goose VLDV-neurophysin are compared to their bovine counterparts, identical substitutions are found in positions 17 (Asn in both goose neurophysins instead of Gly in both ox neurophysins), 18 (Arg instead of Lys), 35 (Tyr instead of Phe), and 41 (Thr instead of Ala). Identity of the sequences 10-74 in both ox neurophysins has been explained by partial gene conversion between oxytocin and vasopressin genes, and identical substitutions in both goose neurophysins might reveal a similar gene conversion between mesotocin and vasopressin genes in birds.

The ostrich pituitary contains a major peptide homologous to mammalian chromogranin A(1-76)

A major peptide related to the NH2-terminal fragment (position 1 to 76) of mammalian chromogranin A was isolated from ostrich adenohypophyses following acid-acetone extraction. The complete amino acid sequence of the homogenous peptide was deduced following automatic Edman degradation of the native peptide as well as of CNBr-, tryptic- and Lysobacter-derived peptides. The 76 amino acid sequence is strikingly homologous to bovine (80.3% sequence identity), porcine (79.0%), human (79.0%) and rat (72.4%) corresponding sequences, but much less so to human chromogranin B (22.4%). As this peptide is followed in bovine, porcine and human structure by a pair of basic residues (Lys-Lys), it could conceivably be produced during maturation in secretory granules. Finally, its structure appears to contain two potential amphipathic helices joined by the single disulfide bridge present in all chromogranin A and B molecules.

Vasotocin and isotocin precursors from the white sucker, Catostomus commersoni: cloning and sequence analysis of the cDNAs

The nucleotide sequences of cloned cDNAs encoding the precursors for vasotocin and isotocin have been elucidated by analyzing a lambda gt11 library constructed from poly(A)+ RNA from the hypothalamic region of the teleost fish Catostomus commersoni. Screening of the library was carried out with synthetic oligonucleotide probes deduced from the amino acid sequences of the nonapeptides vasotocin and isotocin. The cDNA nucleotide sequences predict isotocin and vasotocin prohormone precursors each consisting of a signal peptide, a hormone moiety, and a neurophysin-like molecule. However, in comparison to their mammalian counterparts, both fish neurophysins are extended at their C termini by an approximately 30 amino acid sequence with a leucine-rich core segment. These extensions show striking similarities with the glycopeptide moiety (the so-called copeptin) present in mammalian vasopressin precursors, except that they lack the consensus sequence for N-glycosylation. These data suggest that mammalian copeptin is derived from the C terminus of an ancestral neurophysin.

Ostrich MSEL-neurophysin belongs to the class of two-domain "big" neurophysin as indicated by complete amino acid sequence of the neurophysin/copeptin

Mammalian neurohypophyseal hormones, oxytocin and vasopressin, are known to be synthesized as part of two larger precursors containing, respectively, a VLDV-neurophysin and a MSEL-neurophysin together with its associated glycopeptide. Starting from ostrich neurohypophyses, a "big" neurophysin was isolated and chemically characterized. Following sequence determination of the CNBr-derived fragments and of peptides obtained from trypsin and V8-protease digestion of the oxidized protein, this "big" neurophysin was found to contain an MSEL-neurophysin moiety (94 residues) still covalently associated with the COOH-terminal glycopeptide (38 residues, copeptin). This study demonstrates that the ostrich MSEL-neurophysin sequence closely resembles all known MSEL-neurophysin sequences and that, furthermore, it does not contain the single amino acid insertion shown previously in the ostrich VLDV-neurophysin. It is also shown that the stretch of amino acids, linking the MSEL-neurophysin and the copeptin, is clearly different from its mammalian homologues and lacks the Arg residue normally recognized by the cleaving enzyme. This study also demonstrates that the ostrich copeptin is more closely related to the amphibian copeptin sequence than to its mammalian homologue, leading to the hypothesis that two families of copeptin molecules might exist. Thus, the ostrich MSEL-neurophysin-copeptin molecule is the first "big" neurophysin reported in birds and, together with the guinea pig and amphibian homologues, represents the third example of partial or no neurophysin-copeptin cleavage.

Melanin concentrating hormone. V. Isolation and characterization of alpha-melanocyte-stimulating hormone from frog pituitary glands

The structure of alpha-melanocyte-stimulating hormone (alpha-MSH) has been determined in the pars intermedia of the frog Rana ridibunda. Pulse-chase labeling of frog neurointermediate lobes with selective amino acids revealed that the composition of frog alpha-MSH is similar to that of alpha-MSH from all mammalian species yet studied. Tryptic mapping of nexly synthetized alpha-MSH generated two fragments with the following amino acid composition: (T1) Trp, Pro, Lys, Gly, Val and (T2) Tyr, Arg, Phe, His, Ser, Glu. Concurrently, alpha-MSH was purified from 100 neurointermediate lobes to apparent homogeneity by reverse-phase HPLC. The sequence of the peptide determined by automated Edman degradation was Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val. The structure of frog alpha-MSH is thus identical to mammalian des-N alpha-acetyl alpha-MSH and differs from the sequence of toad (Xenopus laevis) alpha-MSH only by the first residue (Ser instead of Ala). These results confirm that the sequence of alpha-MSH has been highly preserved during evolution.

The amino acid sequences of frog heart atrial natriuretic-like peptide and mammalian ANF are closely related

Despite few studies conducted in non-mammalian species, there has been a number of reports pertaining to the occurrence of a natriuretic-like substance in lower organisms. Thus, an immunoreactive substance reacting with antibodies directed against mammalian atrial natriuretic factor has previously been detected both in heart atria and ventricles of a chordate, the frog. This substance was isolated and purified from frog heart atria and its amino acid sequence established. The sequence, Ala-Pro-Arg-Ser-Ser-Asp-Cys-Phe-Gly-Ser-Arg-Ile-Asp-Arg-Ile-Gly-Ala-Gln- Ser-Gly - Met-Gly-Cys-Gly-Arg-(Phe), is highly homologous to known mammalian ANF sequences. However, when aligned with the complete mammalian ANF precursor sequence at positions 121 to 151, it exhibits a single amino acid insertion at position 129 and other substitutions at positions 121, 125, 133, 135, 144, 147 and 148. Some evidence is also presented concerning the occurrence of uncleaved frog pronatriodilatin, the precursor form of ANF. This study represents the first report pertaining to the structure of a non-mammalian ANF and its precursor.

Synthetic peptide substrates as models to study a pro-ocytocin/neurophysin converting enzyme

The selectivity and mechanism of processing at paired basic amino acids in hormone precursors was studied on several analogues of the (1-20)-aminoterminal domain of the ocytocin/neurophysin precursor in a cleavage assay by an endoprotease partially purified from bovine pituitary secretory granules. Peptide analogues with amino acid substitutions in, and around, the basic doublet were synthesized and used as substrates. The data obtained demonstrate the strict requirement of the processing enzyme for basic amino acids in tandem within a possibly preferred conformation which may be highly conserved in the aminoterminal domain of this hormone precursor.