Primary structure of cholera toxin beta-chain: a glycoprotein hormone analog?

The completed sequence of the beta-chain of cholera toxin (103 amino acid residues) was compared to the beta-chains of chorionic gonadotropin, thyrotropin, luteinizing, and follicle stimulating hormones. The overall chemical similarity of the toxin beta-chain to the hormones was not statistically different from random; however, a comparison of the first 40 residues of the toxin beta-chain to the glycoprotein hormones revealed a segment of the hormones which was significantly chemically similar. The probability was less than .003 that the similarity was due to chance.

Isolation and characterization of the predominant protein in nuclear ribonucleoprotein particles from rat liver.

The predominant protein of the nuclear ribonucleoprotein particles of rat liver was isolated by polyacrylamide gel electrophoresis. The polypeptide represented 35% to 40% of the total mass of the protein moiety. Its molecular weight was estimated to be 38 000 and its NH2-terminal residue was found to be threonine. The amino acid composition is unique in having a high content of glycyl residues (20%) and NG-dimethylarginine (14% of total arginyl residues).

Polypyrimidine tract-binding protein-associated splicing factor is a negative regulator of transcriptional activity of the porcine p450scc insulin-like growth factor response element.

The porcine P-450 cholesterol side-chain cleavage enzyme gene (P450scc) contains a 30-bp region [insulin-like growth factor response element (IGFRE)] that mediates insulin-like growth factor I (IGF-I)-stimulated gene expression and binds Sp1. In this study, we showed that polypyrimidine tract-binding protein (PTB)-associated splicing factor (PSF), an RNA-binding component of spliceosomes, binds to the IGFRE. Southwestern analysis with an IGFRE oligonucleotide showed that a protein (from Sp1-immunodepleted HeLa extract) fractionated on SDS-PAGE at 100 kDa. Microsequence analysis of 100-kDa band HeLa proteins detected PSF. DNA affinity chromatography, using an IGFRE mutant oligonucleotide that does not bind Sp1, isolated a protein that immunoreacted with PSF antibody. Deoxyribonuclease I (DNase I) footprint analysis showed recombinant PSF binds 5' of the Sp1-binding GC box of the IGFRE, and mutant oligonucleotides further delineated this region to a palindrome, CTGAGTC. Functional analysis of these mutants by transfection experiments in a cell line overexpressing the IGF-I receptor (NWTb3) found that an inability to bind PSF significantly increased the IGFRE transcriptional activity, while retaining responsiveness to IGF-I. Moreover, transfection of expression vectors for Sp1 and PSF in porcine granulosa cells found that Sp1 expression stimulated IGFRE transcriptional activity while PSF inhibited activity even with coexpression of Sp1. In conclusion, we identified PSF as an independent, inhibitory regulator of the transcriptional activity of the porcine P450scc IGFRE.

A recombinant extracellular domain of the thyrotropin (TSH) receptor binds TSH in the absence of membranes.

We produced large quantities of the extracellular domain of the human TSH receptor (ETSHR) using the baculovirus expression system. Insect cells containing the ETSHR protein were sequentially extracted using lysis, nuclease, and high salt buffers to enrich for recombinant protein. The ETSHR protein was purified to homogeneity on a C4 reverse phase semipreparative column using HPLC. The recombinant protein was identified as ETSHR by immunoreactivity with antibodies prepared against TSHR-derived synthetic peptides. The identity of the ETSHR was further confirmed by amino acid compositional analyses, which agreed with the amino acid composition predicted from reported cDNA sequence analyses. Protein sequence analyses confirmed that the first 26 amino acids of the N-terminal region and the C-terminal amino acid were identical to the predicted amino acid sequence. The purified ETSHR was refolded in the presence of 1.5 M guanidine-HCl and 1 mM each of cystine and cysteine. [125I] TSH bound to the refolded ETSHR in vitro in a dose-dependent manner and was specifically blocked by unlabeled TSH, but not by LH or FSH. It was notable that a membrane requirement was not essential for TSH to bind to ETSHR.

Biosynthesis of rabbit haptoglobin: chemical evidence for a single chain precursor.

The primary translation product of the mRNA for rabbit haptoglobin was obtained from a rabbit reticulocyte lysate cell-free system by immunoprecipitation with an antiserum that was directed to the beta chain of haptoglobin. Analysis of the translation product by gel electrophoresis and by protein sequencing analysis identified a single polypeptide of Mr 41 000. Sequence analysis established a signal region of 18 residues that was immediately followed by the alpha chain sequence. These results give strong evidence that haptoglobin is initially synthesized as a single chain composed of a signal peptide followed by alpha and beta chain regions, respectively.

Structural characterization of a Lymnaea putative endoprotease related to human furin.

A number of peptides have been identified in the central nervous system of the freshwater snail, Lymnaea stagnalis, that function as hormones and neurotransmitters/neuromodulators. These peptides are typically proteolytically processed from larger prohormones mostly at sites composed of single or multiple basic amino acid residues. Previously we demonstrated a diversity of putative prohormone convertases that may be involved in prohormone processing in the Lymnaea brain. In the present report, we have characterized a cDNA clone encoding a putative endoprotease of 837 amino acids. The primary structure of endoprotease (Lfur2) was comparable to that of human furin and contained a putative catalytic domain, a Cys-rich domain, and a transmembrane region. The catalytic domain of Lfur2 demonstrated about 70% residue identity when compared with human furin, PACE4 and Drosophila Dfur1 and dKLIP-1. The Lfur2 gene was expressed in the central nervous system as well as various peripheral tissues of Lymnaea.

Broad antiviral activity in tissues of crustaceans.

Innate antiviral substances occur in vertebrates and may function as host defenses. Virus infections are common among invertebrates, but little is known about the ability of invertebrates to control viral infections. Pre-existing antiviral substances may be particularly important, since invertebrates lack the antiviral defense conferred by specific immunity. In our study, we found that tissue extracts of blue crab (Callinectes sapidus), shrimp (Penaeus setiferus), and crayfish (Procambarus clarkii) contained antiviral activities that inhibit a variety of DNA and RNA viruses, i.e. Sindbis virus (SB), vaccinia virus (VAC), vesicular stomatitis virus (VS), mengo virus (MENGO), banzi virus (BANZI) and poliomyelitis (POLIO). The concentration of inhibitory activity was relatively high, ranging from 102 to 216 U/g tissue for Sindbis virus, using the various tissue extracts. The other viruses were somewhat less sensitive to the inhibitor. The main antiviral activity in the inhibitor preparation from blue crab resided in an approximately 440 kDa fraction. It was inactivated significantly by lipid extraction, but not by proteinase K or glycosidases. The antiviral mechanism of the inhibitor from the blue crab was inhibition of virus attachment to eukaryotic cells, as evidenced by inhibitory activity at 4 degrees C. These studies are among the first to show the existence of broadly active antiviral activities in aquatic crustaceans. These antiviral substances may function as innate host defenses in these species that lack specific antibody immunity and, therefore, merit further study.

Molecular cloning of prohormone convertase 1 from the atrial gland of Aplysia.

We have screened an Aplysia atrial gland cDNA library using a prohormone convertase (PC)1 probe prepared by polymerase chain reaction (PCR) and have isolated an Aplysia PC1-related full-length 3.6-kb cDNA clone. The cDNA sequence (3,565 bp) encoded a putative preproendoprotease (APC1) of 703 amino acid residues that showed considerable sequence identity with other eukaryotic PC1s, and indicated a high degree of sequence identity with an Aplysia nervous system PC sequence (aPC1B). Northern blot analysis of atrial gland RNA identified two APC1 transcripts of 3.9 kb and 5.0 kb. APC1 is a candidate PC that may play an important role in the processing of egg-laying hormone (ELH)-related precursors in atrial gland secretory cells and represents one of the first examples of PC1 expression in an exocrine tissue.

Molecular cloning, cDNA sequence, and localization of a prohormone convertase (PC2) from the Aplysia atrial gland.

Neuropeptides and peptide hormones are synthesized as part of larger precursor proteins that are processed post-translationally by subtilisin-related calcium-dependent prohormone convertases (PCs), frequently at multiple basic sites, to generate biologically active peptides. The atrial gland of Aplysia californica produces large quantities of egg-laying hormone (ELH)-related peptides, providing a unique opportunity to study prohormone processing. We have screened an Aplysia atrial gland cDNA library using a Lymnaea stagnalis PC2 probe and have isolated an Aplysia PC2-related 4.6-kb cDNA partial clone that was truncated on the 5' end. The remaining 5' atrial gland PC2 nucleotide sequence was obtained by reverse transcription/polymerase chain reaction (RT-PCR). The composite cDNA structure (5.6 kb) was deduced from sequence analysis of the RT-PCR product combined with the sequence obtained from the cDNA clone. The deduced cDNA of Aplysia atrial gland PC2 encoded a putative preproendoprotease of 653 amino acids that was evolutionarily related to other eukaryotic PC2s, and showed the strongest sequence identity with recently reported Aplysia nervous tissue PC2 sequences. In situ hybridization demonstrated extensive expression of PC2 in atrial gland secretory cells. The cDNA clone contained a relatively long 3'untranslated region (3'-UTR) of 3,632 nucleotides. Strikingly, the 3'-UTR also contained several major nucleotide repeat sequences including the microsatellite repeats, (CA)n and (TG)n, and a TA-rich region comprised largely of the triplet repeat (TTA)n. The characterized Aplysia PC2 is a candidate endoprotease that may play an important role in the processing of ELH-related precursors in the atrial gland and represents the first example of PC2 expression in exocrine tissue.

Molecular cloning and cellular localization of a furin-like prohormone convertase from the atrial gland of Aplysia.

Prohormone convertases (PCs) are Ca(2+)-dependent subtilisin-related endoproteases that have been implicated in the post-translational processing of prohormones and other proproteins. Furin is an ubiquitously expressed PC that has been shown to hydrolyze a wide variety of precursor proteins in secretory pathways. We have screened an Aplysia atrial gland cDNA library using a furin probe prepared by polymerase chain reaction (PCR) and have isolated an Aplysia furin-related 6.7-kb cDNA partial clone that was truncated on the 5' end. The remaining 5' atrial gland furin nucleotide sequence was obtained by two stages of reverse transcription PCR. The final composite nucleotide sequence of the atrial gland furin cDNA was 7,837 bp in length. This sequence encoded a putative preproendoprotease (Afurin2) of 824 amino acid residues that was related to other eukaryotic furins, and showed a high sequence identity with a recently reported Aplysia nervous system furin-like sequence. In situ hybridization demonstrated extensive expression of Afurin2 in atrial gland secretory cells. The cDNA clone contained a relatively long 3' untranslated region of 5,230 nucleotides that included a microsatellite repeat region (TG)n. The characterized Aplysia Afurin2 is a candidate PC that may play an important role in the processing of egg-laying hormone (ELH)-related precursors in the secretory cells of the atrial gland. In addition, comparative structural studies of Afurin2, together with previously reported localization studies, argue for the occurrence of a furin-like convertase within secretory granules.

Peptide biotinylation with amine-reactive esters: differential side chain reactivity.

N-hydroxysuccinimide (NHS) esters of biotin are reported to react specifically with amino groups of peptides and proteins. However, we have found that these reagents can readily acylate other functional groups in specific peptide sequences under relatively mild conditions. We have extended our inquiry of sequence-dependent acylation by evaluating the reactivity of a variety of commonly employed biotinylation reagents typically used for amino group modification. These included the p-nitrophenyl ester of biotin, NHS-esters of biotin containing aminohexanoic acid spacer arms, and a sulfonated NHS-biotin ester that contained a disulfide bond within its spacer. The decapeptide [D-Lys6]gonadotropin releasing hormone was employed as a model peptide. Reaction products were characterized by high-performance liquid chromatography, amino acid compositional analysis, reaction with hydroxylamine, and mass spectrometry. In addition to the O-acylation of Ser4 and Tyr5 in this peptide, we have also identified a novel biotinylation of the Arg8 side chain.

Purification and characterization of Aplysia atrial gland secretory granules containing egg-laying prohormone-related peptides.

A purification scheme is described for the isolation of secretory granules containing egg-laying prohormone-related peptides from the atrial gland of Aplysia californica, an exocrine organ in the reproductive tract. Granules were purified by differential centrifugation of atrial gland homogenates followed by centrifugation on continuous Percoll-sucrose gradients. Quantitative enzyme assays in conjunction with electron microscopic analyses demonstrated that secretory granules thus isolated were significantly purified with respect to other subcellular organelles such as mitochondria and lysosomes. Immunoelectron microscopy demonstrated that the majority (approximately 85%) of the purified secretory granules were immunoreactive for A-NTP (N-terminal peptide), a cleavage product of the egg-laying prohormone-related A and A' precursors (residues 22-34). The purified granules represented an enriched source of peptides that were readily resolved by reversed-phase high performance liquid chromatography.

The bag cell egg-laying hormones of Aplysia brasiliana and Aplysia californica are identical.

Egg laying in the marine molluscan genus Aplysia is elicited by an egg-laying hormone (ELH) which induces ovulation and acts on central neurons to effect egg-laying behavior. ELH, isolated from the A. californica bag cells, and three ELH-related peptides, isolated from the A. californica atrial gland, have been chemically characterized, yet relatively little is known about homologous peptides in other Aplysia species. In these studies, the primary structure of A. brasiliana ELH was determined. Bag cell clusters were extracted in an acidic solution, and the peptides purified by sequential gel filtration and reversed-phase HPLC; ELH was identified by bioassay. Amino acid compositional and sequence analyses demonstrated that the neurohormone was a 36-residue peptide whose sequence was identical to that of A. californica ELH: NH2-Ile-Ser-Ile-Asn-Gln-Asp-Leu-Lys-Ala-Ile-Thr-Asp-Met-Leu-Leu-Thr-Glu- Gln-Ile- Arg-Glu-Arg-Gln-Arg-Tyr-Leu-Ala-Asp-Leu-Arg-Gln-Arg-Leu-Leu-Glu-Lys-COOH .

Aplysia brasiliana neurons R3-R14: primary structure of the myoactive histidine-rich basic peptide and its prohormone.

Neurons R3-R14 of the marine mollusc Aplysia are model neuroendocrine cells thought to regulate cardiovascular activity in vivo. The cells express a gene encoding three peptides--peptides I, II and the histidine-rich basic peptide (HRBP)--each of which has been chemically characterized in Aplysia californica. In the studies presented here, HRBP and its prohormone (proHRBP) were purified from A. brasiliana abdominal ganglion extracts by reversed-phase high-performance liquid chromatography and characterized by amino acid compositional and sequence analyses. ProHRBP was an 85-residue peptide whose sequence was: NH2-Glu-Glu-Val-Phe-Asp-Asp-Thr-Asp-Val-Gly-Asp-Glu-Leu-Thr-Asn-Ala-Leu- Glu-Ser - Val-Leu-Thr-Asp-Leu-Lys-Asp-Lys-Arg-Asp-Ala-Glu-Glu-Pro-Ser-Ala-Phe-Met- Thr-Arg - Leu-Arg-Arg-Gln-Val-Ala-Gln-Met-His-Ile-Trp-Arg-Ala-Asn-His-Asp-Arg-His- His-Ser - Thr-Gly-Ser-Gly-Arg-His-Ser-Arg-Phe-Leu-Thr-Arg-Asn-Arg-Tyr-Gly-Gly-Gly- His-Leu - Ser-Asp-Ala-COOG. It differed from A. californica pro-HRBP at seven of the 85 positions. Compositional and sequence analyses demonstrated that A. brasiliana HRBP was a 43-residue peptide corresponding to residues 43 through 85 of proHRBP, and that a significant proportion of the isolated peptide possessed a blocked NH2 terminus. Although this sequence differed from that of A. californica HRBP at five of 43 residues, the two peptides were approximately equipotent in inducing contractions of A. californica crop muscle in vitro, suggesting that the substituted residues may not be critical for biological activity.

Aplysia californica neurons R3-R14: primary structure of the myoactive histidine-rich basic peptide and peptide I.

The R3-R14 neurons of the marine mollusc Aplysia are neuroendocrine cells that express a gene encoding peptides I, II and histidine-rich basic peptide (HRBP), a myoactive peptide that excites Aplysia heart and enhances gut motility in vitro. Peptide II has been chemically characterized (35), but the complete primary structures of peptide I and HRBP have not been established by amino acid sequence analysis. HRBP, peptide I, and the prohormone (proHRBP) were therefore purified from acid extracts of Aplysia californica neural tissue using sequential gel filtration and reverse-phase high-performance liquid chromatography and chemically characterized. Amino acid sequence analysis demonstrated that HRBP was a 43-residue peptide whose sequence was: less than Glu-Val-Ala-Gln-Met-His-Val-Trp-Arg-Ala-Val-Asn-His-Asp-Arg-Asn-His-Gly- Thr-Gly - Ser-Gly-Arg-His-Gly-Arg-Phe-Leu-Ile-Arg-Asn-Arg-Tyr-Arg-Tyr-Gly-Gly-Gly- His-Leu - Ser-Asp-Ala-COOH. Compositional and sequence analyses of peptide I and proHRBP demonstrated that peptide I was a 26-residue peptide with the following sequence: NH2-Glu-Glu-Val-Phe-Asp-Asp-Thr-Asp-Val-Gly-Asp-Glu-Leu-Thr-Asn-Ala- Leu-Glu-Ser-Val-Leu-Thr-Asp-Phe-Lys-Asp-COOH. These results demonstrated that the pro-HRBP sequence predicted by nucleotide sequence analysis of a cDNA clone (24) was in fact synthesized in R3-R14 neurons. Hydrophilicity and hydrophobicity profiles of preproHRBP, combined with charge distribution profiles and predictive secondary structural analysis, showed that cleavage at dibasic sequences was strongly associated with peaks of hydrophilicity in alpha-helical regions of the preprohormone.

Genetic variation in related cytolytic toxins produced by different species of Aeromonas.

Comparative analyses were performed at the immunological, biological, and genetic level to establish the degree of relatedness of a group of four cytotoxic enterotoxins and aerolysins produced by different isolates of Aeromonas: SSU [16], Ah1 [13], Ah2 [18], and Ah65 [21]. Results obtained from Western blot analysis, neutralization studies, and Southern blot analysis indicated that although the members of this group of toxins displayed structural similarities they also differed from each other at the immunological, biological and genetic level.

Prohormone convertase-1 is essential for conversion of chromogranin A to pancreastatin.

The purpose of this study was to test the hypothesis that the endoprotease, prohormone convertase-1 (PC-1), is involved in the processing of the precursor protein chromogranin A (CGA) to a smaller peptide called pancreastatin (PST). A human pancreatic carcinoid cell line (BON) that expresses PC-1, CGA and PST was stably transfected with antisense PC-1 mRNA. BON cells expressing antisense PC-1 mRNA showed nearly complete abolishment of PC-1 protein (approximately 95% reduction) and an 80% reduction in cell content of PST immunoreactivity (PST-IR) as assessed by high-performance liquid chromatography in combination with measurement of PST-IR. These findings indicate that PC-1 is essential for processing CGA to PST.

Expression and genetic variation of the Aplysia egg-laying hormone gene family in the atrial gland.

We have screened an Aplysia atrial gland cDNA library using an egg-laying hormone (ELH) precursor probe and have isolated and characterized five different clones, four of which are full-length and approximately 0.8 kb in size. The characterization of these cDNA clones firmly established the genetic variation of the ELH-related precursors expressed in the atrial gland and provided a rational basis for their revised nomenclature proposed herein. The five precursor ELH-related cDNA sequences obtained predicted the following genetically distinct polypeptide precursors designated as: A, [Asp143]A, [Glu94,Gln139]A, [Pro25]B, and [Phe96,Asp107]BT. The [Phe96,Asp107]Br cDNA sequence predicted a truncated form of a B-type precursor. Northern blot analysis of atrial gland RNA identified two transcripts of about equal intensity of 0.9 kb and 1.1 kb. Polymerase chain reaction of genomic DNA, together with DNA sequence analysis, resolved previously reported discrepancies between genomic and cDNA sequences of the ELH-related precursors. Taken together the results obtained identified the expression of five ELH-related precursor genes in the atrial gland of Aplysia from at least two genetic loci per haploid genome.

Amino acid sequence of penicillopepsin. I. Isolation and characterization of the chymotryptic peptides.

The amino acid sequences of 48 peptides obtained from a chymotryptic digest of the mould acid protease, penicillopepsin (EC 3.4.23.7), have been determined. These peptides established the sequences of 26 unique fragments of up to 28 residues in length. The 28-residue fragment was identified as the N-terminal region. The C terminal region is represented by a 13-residue fragment. The amino acids contained in these fragments account for some 85% of the residues of the enzyme.