Structure and receptor-binding activity of insulin from a holostean fish, the bowfin (Amia calva)

Glucagon-like peptides-1 from phylogenetically ancient fish show potent anti-diabetic activities by acting as dual GLP1R and GCGR agonists

Glucagon-like peptides-1 (GLP-1)from phylogenetically ancient fish (lamprey, dogfish, ratfish, paddlefish and bowfin) and from a teleost, the rainbow trout produced concentration-dependent stimulations of insulin release from clonal β-cells and isolated mouse islets. Lamprey and paddlefish GLP-1 were the most potent and effective. Incubation of BRIN-BD11 cells with GLP-1 receptor (GLP1R) antagonist, exendin-4 (9-39) attenuated insulinotropic activity of all peptides whereas glucagon receptor (GCGR) antagonist [des-His¹,Pro⁴,Glu⁹] glucagon amide significantly decreased the activities of lamprey and paddlefish GLP-1 only. The GIP receptor antagonist GIP (6-30) Cex-K⁴⁰ [Pal] attenuated the activity of bowfin GLP-1. All peptides (1 μM) produced significant increases in cAMP concentration in CHL cells transfected with GLP1R but only lamprey and paddlefish GLP-1 stimulated cAMP production in HEK293 cells transfected with GCGR. Intraperitoneal administration of lamprey and paddlefish GLP-1 (25 nmol/kg body weight) in mice produced significant decreases in blood glucose and increased insulin concentrations comparable to the effects of human GLP-1. Lamprey and paddlefish GLP-1 display potent insulinotropic activity in vitro and glucose-lowering activity in vivo that is mediated through GLP1R and GCGR so that these peptides may constitute templates for design of new antidiabetic drugs.

The endocrine cells in the gastroenteropancreatic system of the bowfin, Amia calva L.: an immunohistochemical, ultrastructural, and immunocytochemical analysis

The gastroenteropancreatic (GEP) endocrine system of bowfin (Amia calva) was described using light and electron microscopy and immunological methods. The islet organ (endocrine pancreas) consists of diffusely scattered, mostly small islets and isolated patches of cells among and within the exocrine acini. The islets are composed of abundant, centrally located B cells immunoreactive to bovine and lamprey insulin antisera and D cells showing a widespread distribution and specificity to somatostatin antibodies. A and F cells are present at the very periphery of the islets and are immunoreactive with antisera against glucagon (and glucagon-like peptide) and several peptides of the pancreatic polypeptide (PP)-family, respectively. The peptides of the two families usually collocates within the same peripheral islet cells and are the most common immunoreactive peptides present in the extra-islet tissue. Immunocytochemistry and fine structural observations characterised the granule morphology for B and D cells and identified two cell types with granules immunoreactive to glucagon antisera. These two putative A cells had similar granules, which were distinct from either B or D cells, but one of the cells had rod-shaped cytoplasmic inclusions within cisternae of what appeared to be rough endoplasmic reticulum. The inclusions were not immunoreactive to either insulin or glucagon antisera. Only small numbers of cells in the stomach and intestine immunoreacted to antisera against somatostatin, glucagon, and PP-family peptides. The paucity of these cells was reflected in the low concentrations of these peptides in intestinal extracts. The GEP system of bowfin is not unlike that of other actinopterygian fishes, but there are some marked differences that may reflect the antiquity of this system and/or may be a consequence of the ontogeny of this system in this species.

Evolution of the insulin molecule: insights into structure-activity and phylogenetic relationships

The conformation of insulin in the crystalline state has been known for more than 30 years but there remains uncertainty regarding the biologically active conformation and the structural features that constitute the receptor-binding domain. The primary structure of insulin has been determined for at least 100 vertebrate species. In addition to the invariant cysteines, only ten amino acids (GlyA1, IleA2, ValA3, TyrA19, LeuB6, GlyB8, LeuB11, ValB12, GlyB23 and PheB24) have been fully conserved during vertebrate evolution. This observation supports the hypothesis derived from alanine-scanning mutagenesis studies that five of these invariant residues (IleA2, ValA3, TyrA19, GlyB23, and Phe24) interact directly with the receptor and five additional conserved residues (LeuB6, GlyB8, LeuB11, GluB13 and PheB25) are important in maintaining the receptor-binding conformation. With the exception of the hagfish, only conservative substitutions are found at B13 (Glu --> Asp) and B25(Phe --> Tyr). In contrast, amino acid residues that were also considered to be important in receptor binding based upon the crystal structure of insulin (GluA4, GlnA5, AsnA21, TyrB16, TyrB26) have been much less well conserved and are probably not components of the receptor-binding domain. The hypothesis that LeuA13 and LeuB17 form part of a second receptor-binding site in the insulin molecule finds some support in terms of their conservation during vertebrate evolution, although the site is probably absent in some hystricomorph insulins. In general, the amino acid sequences of insulins are not useful in cladistic analyses especially when evolutionary distant taxa are compared but, among related species in a particular order or family, the presence of unusual structural features in the insulin molecule may permit a meaningful phylogenetic inference. For example, analysis of insulin sequences supports monophyletic status for Dipnoi, Elasmobranchii, Holocephali and Petromyzontiformes.

Molecular cloning of preproinsulin cDNAs from several osteoglossomorphs and a cyprinid

Several preproinsulin cDNAs were isolated and characterized from four members of the Osteoglossomorpha (an ancient teleost group); Osteoglossum bicirrhosum (arawana), Pantodon buchholzi (butterfly fish), Notopterus chitala (feather fin knife fish), Hiodon alosoides (goldeye) and Gnathonemus petersii (elephantnose). In addition, we isolated and characterized the preproinsulin cDNA from Catostomus commersoni (white sucker, as a representative of a generalized teleost). The comparative analysis of the sequences revealed conservation of the cystine residues known to be involved in the formation of the disulfide bridges, as well as residues involved in the hexamer formation, except for B-17 in the butterfly fish, the arawana and the goldeye. However, the N-terminus of the B-chain was very weakly conserved among the species studied. Residues known to be significant for maintaining receptor-binding conformation and those known to comprise the receptor-binding domain were all conserved, except for a conservative substitution at B13, aspartate substituted glutamate in the arawana, goldeye, butterfly fish and white sucker, and at B16, phenylalanine substituted tyrosine in the elephantnose. Phylogenetic analysis of the sequences revealed a monophyletic grouping of the osteoglossomorphs, and showed that they were not the most basal living teleost. Comparative sequence analysis of preproinsulins among the osteoglossomorphs was useful in assessment of intergroup relationship, relating elephantnose with the feather fin knife fish and the arawana, butterfly fish, and goldeye. This arrangement of species is consistent with relationships based on other more classical parameters, except for the goldeye which was assessed as being sister to all the osteoglossomorphs. The white sucker was grouped with the common carp and both are cyprinids.

Multiple molecular forms of glucagon and insulin in the kaluga sturgeon, Huso dauricus

Five molecular forms of glucagon and two molecular forms of insulin were characterized from the kaluga sturgeon. Substitutions occurred at two to thirteen internal amino acid residues among the five molecular forms of glucagons, indicating that these glucagons were encoded by five distinct genes. The amino acid sequences of two insulins from the kaluga sturgeon were identical to those of paddlefish insulin-II and Russian sturgeon insulin except that kaluga sturgeon insulin-I had an extension of five residues at the B-chain N-terminus. This is the first demonstration that more than two molecular forms of glucagon have been characterized from a single animal species.

Gastroenteropancreatic hormones (insulin, glucagon, somatostatin, and multiple forms of PYY) from the pallid sturgeon, Scaphirhynchus albus (Acipenseriformes)

Insulin, glucagon, somatostatin-14, and three structurally related molecular forms of peptide tyrosine-tyrosine (PYY) were isolated from an extract of the combined pancreas and gastrointestinal tract of the pallid sturgeon, Scaphirhynchus albus. Pallid sturgeon insulin was identical to insulin from the Russian sturgeon, Acipenser guldenstaedti, and to insulin-2 from the paddlefish, Polyodon spathula, and was approximately twofold less potent than human insulin in inhibiting the binding of [3-[(125)I] iodotyrosine-A14] human insulin to the soluble human insulin receptor. The sturgeon glucagon (HSQGMFTNDY(10)-SKYLEEKLAQ(20) EFVEWLKNGK(30)S), like the two paddlefish glucagons, contains 31 rather than 29 amino acid residues, indicative of an anomalous pathway of posttranslational processing of proglucagon. Pallid sturgeon somatostatin, identical to human somatostatin-14, was also isolated in a second molecular form containing an oxidized tryptophan residue, but [Pro(2)]somatostatin-14, previously isolated from the pituitary of A. guldenstaedti, was not identified. Sturgeon PYY (FPPKPEHPGD(10)DAPAEDVAKY(20)YTALRHYINL(30) ITRQRY.HN(2)) was also isolated in variant forms containing the substitutions (Phe(1) --> Ala) and (Ala(18) --> Val), indicative of at least two gene duplications occurring within the Acipenseriformes lineage. The amino acid sequences of the pallidsturgeon PYY peptides are appreciably different from the proposed "ancestral" PYY sequence that has otherwise been very strongly conserved among the actinopterygian and elasmobranch fish.

Isolation and characterization of insulin from the Brockmann body of Dissostichus mawsoni, an Antarctic teleost fish

The Brockmann body of fish synthesizes and secretes insulin. The Brockmann body of Antarctic fish has been described anatomically and shown to contain insulin immunoreactive sites, however, the primary structure of an Antarctic fish insulin has yet to be reported. Insulin was isolated from the Brockmann bodies of the Antarctic perciform teleost, Dissostichus mawsoni. The peptide was purified to homogeneity by gel filtration and reversed-phase HPLC. Insulin-containing fractions were identified by radioimmunoassay using antisera raised against porcine insulin. Electrospray ionization-mass spectrometry determined the mass of the isolated product to be 5725.27 a.m.u. The amino acid composition and primary structure were determined for the pyridylethylated A- and B-chains. The amino acid sequences of the A chain and B chain were H-Gly-lle-Val-Glu-Gln-Cys-Cys-His-Gln-Pro10-Cys-Asn-Ile-Phe- Asp-Leu-Gln-Asn-Tyr-Cys20-Asn-OH and H-Ala-Pro-Gly-Pro-GIn-His-Leu-Cys-Gly-Ser10-His-Leu-Val-Asp-Ala-Le u-Tyr-Leu-Val-Cys20-Gly-Glu-Arg-Gly-Phe-Phe-Tyr-Asn-Pro-Lys30++ +-OH, respectively. The primary structure of insulin from Antarctic fish is compared with known structures of insulin from other vertebrates.

Insulin, insulin-like growth factor-I (IGF-I) and glucagon: the evolution of their receptors

Insulin and glucagon, two of the most studied pancreatic hormones bind to specific membrane receptors to exert their biological actions. Insulin-like growth factors IGF-I and IGF-II are structurally related to insulin, although they are expressed ubiquitously. The biological functions of the IGFs are mediated by different transmembrane receptors, which includes the insulin, IGF-I and IGF-II receptors. The interaction of insulin, insulin related peptides and glucagon with the corresponding receptors has been studied extensively in mammals and continues to be so. At the same time, research on ectothermic animals has made enormous progress in the recent years. This paper summarizes current knowledge on insulin, IGF-I and glucagon receptors, from a comparative point of view with special attention to non-mammalian vertebrates. The review covers adult and mostly typical target tissues, and with very few exceptions, developmental aspects are not considered. Binding characteristics, tissue distribution and structure of insulin and IGF-I receptors will be considered first, because both ligands and receptors are structurally related and have overlapping functions. These sections will be followed by similar distribution of information on glucagon receptors. Readers interested in either structure or functions of insulin, IGFs and glucagon in nonmammalian vertebrates are referred to other reviews (Mommsen TP, Plisetskaya EM. Insulin in fishes and agnathans: history, structure and metabolic regulation. Rev Aquat Sci 1991;4:225-259; Mommsen TP, Plisetskaya EM. Metabolic and endocrine functions of glucagon-like peptides: evolutionary and biochemical perspectives. Fish Physiol Biochem 1993;11:429-438; Duguay SJ, Mommsen TP. Molecular aspects of pancreatic peptides. In: Sherwood NM, Hew CL, editors, Fish Physiology. vol 13. 1994:225-271; Plisetskaya EM, Mommsen TP. Glucagon and glucagon-like peptides in fishes. Int Rev Citol 1996;168:187-257.).

Ranatuerins: antimicrobial peptides isolated from the skin of the American bullfrog, Rana catesbeiana

Nine peptides, termed ranatuerins 1-9, with antimicrobial activity towards Staphylococcus aureus, were isolated from an extract of the skin of the adult American bullfrog, Rana catesbeiana. In common with other cytolytic peptides from Ranid frogs, (e.g. ranalexin, gaegurins, brevinins), ranatuerins 1 and 4 contain an intramolecular disulfide bridge forming a heptapeptide ring whereas in ranatuerins 2 and 3 the disulfide bridge forms a hexapeptide ring. The structurally related ranatuerins 5-9 comprise 12 - 14 amino acids and show sequence similarity towards the hemolytic peptides A1 and B9 previously isolated from the skin of Rana esculenta. Of the peptides purified, ranatuerin 1 (SMLSVLKNLGKVGLG FVACKINKQC) showed the broadest spectrum of antimicrobial action with inhibitory activity against S. aureus, Escherichia coli and Candida albicans.

Isolation and characterization of insulin in Russian sturgeon (Acipenser guldenstaedti)

Insulin was isolated from the pancreas of Chondrostean fish, the Russian sturgeon, Acipenser guldenstaedti, by acid-ethanol extraction followed by ion-exchange and reverse-phase high-performance liquid chromatographies. The amino acid sequence determined by automated Edman degradation is as follows: A-chain (21-amino-acid peptide), H-Gly-Ile-Val-Glu-Gln-Cys-Cys-His-Ser-Pro-Cys-Ser-Leu-Tyr-Asp-Leu-Glu-As n-Tyr-Cys-Asn-OH; and B-chain (31-amino-acid peptide), H-Ala-Ala-Asn-Gln-His-Leu-Cys-Gly-Ser-His-Leu-Val-Glu-Ala-Leu-Tyr-Leu-Va l-Cys-Gly-Glu-Arg-Gly-Phe-Phe-Tyr-Thr-Pro-Asn-Lys-Val-OH. The sturgeon insulin appears to be identical with one of two forms of paddlefish insulin and differs from the other form by a single substitution in the A-chain, Asp15: His15. The amino acid sequence of sturgeon insulin is more similar to the amino acid sequence of mammalian insulins than of other fish insulins. Sturgeon insulin showed parallel but weaker displacement than porcine insulin and pink salmon insulin in their respective radioimmunoassays and was less potent than porcine insulin in displacing radiolabeled porcine insulin bound to partially purified rat liver plasma membranes.

Purification and structural characterization of insulin and glucagon from the bichir Polypterus senegalis (Actinopterygii: Polypteriformes)

The Polypteriformes (bichirs and reedfish) are a family of ray-finned fishes of ancient lineage. Insulin has been isolated from an extract of the pancreas and upper gastrointestinal tract of the bichir Polypterus senegalis and its primary structure established as A-chain: Gly-Ile-Val-Glu-Gln-Cys-Cys-Asp-Thr-Pro10-Cys-Ser- Leu-Tyr-Asp-Leu-Glu-Asn-Tyr-Cys20-Asn: B-chain: Ala-Ala-Asn-Arg-His-Leu-Cys-Gly-Ser-His10-Leu-Val- Glu-Ala-Leu-Tyr-Leu-Val-Cys-Gly20-Asn-Arg-Gly-Phe- Phe-Tyr-Ile-Pro-Ser-Lys30-Met. Despite the fact that Polypterus insulin contains several unusual structural features that are not found in insulins from other jawed fish (Asp at A-8, Thr at A-9, Arg at B-4, Asn at B-21, Ile at B-27, Met at B-31), all the residues in human insulin that are involved in receptor binding, dimerization, and hexamerization have been conserved. A comparison of the structures of insulins from a range of species indicates that Polypterus insulin most closely resembles paddlefish insulin II (seven amino acid substitutions). In contrast, Polypterus glucagon (His-Ser- Gln-Gly-Thr-Phe-Thr-Asn-Asp-Tyr10-Thr-Lys-Tyr- Gln-Asp-Ser-Arg-Arg-Ala-Gln20-Asp-Phe-Val-Gln- Trp-Leu-Met-Ser-Asn) most closely resembles the glucagons from the gar Lepisosteus spatula and the bowfin Amia calva (four amino acid substitutions). The data are consistent with the conclusion based on comparison of morphological characteristics that the Polypterids are the most basal living group of the Actinopterygians with evolutionary connections to both the Acipenserids and the Neopterygians.

Primary structure of insulin from the african lungfish, Protopterus annectens

Among the extant Sarcopterygii, the interrelationship between the Dipnoi (lungfishes), Actinistia (coelacanths), and Tetrapoda (tetrapods) is controversial. Insulin has been purified from an extract of the pancreas of the African lungfish Protopterus annectens and its primary structure established as A-chain, Gly-Ile-Val-Glu-Gln-Cys-Cys-His-Lys-Pro10-Cys-Ser-Leu- Tyr -Glu-Leu-Glu-Asn-Tyr-Cys20-Asn-Val-Pro; and B-chain, Ala-Val-Leu-Asn-Gln-His-Leu-Cys-Gly-Ser10-His-Leu-Val- Glu- Ala-Leu-Tyr-Leu-Val-Cys20-Ala-Asp-Asn-Gly-Phe- Phe-Tyr-Lys-Pro-Ser30-Gly. Lungfish insulin contains unusual structural features, such as the dipeptide extension to the C-terminus of the A-chain and the substitution Arg --> Asn at position B-23 in the putative receptor binding region of insulin, which may be expected to influence appreciably its biological potency relative to mammalian insulins. Lungfish insulin also contains amino acid substitutions such as Gly --> Ala at position B-21, Glu --> Asp at position B-22, and a Lys --> Ser residue at position B-30, previously found in insulins from amphibia. This observation is consistent with paleontological data suggesting that lungfish and amphibia share a close phylogenetic relationship.

An immunohistochemical study of the endocrine cells within the pancreas, intestine, and stomach of the gar (Lepisosteus osseus L.)

The distribution and identity of the various endocrine cell types were examined in the pancreas, stomach, and anterior intestine of the phylogenetically ancient actinopterygian, the gar (Lepisosteus osseus L.), using immunohistochemistry. Antisera used were directed against several insulins (INSs) and somatostatins (SSTs), and members of the pancreatic polypeptide (PP, aPY, NPY) and glucagon (GLUC, GLP) families. In the gar pancreas the most pronounced aggregation of islet tissue is among the exocrine acini near the union of extrahepatic common bile duct with the gastrointestinal junction. Four immunoreactive cell types were identified within well-defined islets (A, B, D, and F cells) but immunoreactive cell types were also seen isolated among the exocrine acini. Centrally located B cells were immunoreactive with mammalian and lamprey INS antisera whereas the widely dispersed D cells immunostained with anti-SST-14, -25, and -34. SST was also localized in the epithelium of the pancreatic ducts. There was a colocalization of immunoreactivity for each member of the PP and GLU families at the periphery of each islet to identify F and A cells, respectively. However, colocalization of peptides from both families is suspected for at least some cells. Although the gastric and intestinal mucosae showed a similar pattern of immunoreactivity to GLP and not GLU, they had contrasting immunoreactivity with the two INS antisera. SST immunoreactivity was restricted to the stomach, whereas three of the four PP-family peptides were only immunoreactive in the intestine. Immunoreactivity to the various antisera used in the study imply that there may be an organ-specific processing of preproinsulin, that the gar SST profile may be more similar to agnathan and bowfin rather than either elasmobranch or teleost SSTs, and that only the GLP portion of the preproglucagon gene is expressed in the gastrointestinal mucosa. Our results are consistent with other recent endocrine studies showing that the gar is a widely distinct actinopterygian.

Isolation of a peptide structurally related to mammalian corticostatins from the lamprey Petromyzon marinus

Peptides in an extract of skin from the agnathan Petromyzon marinus (sea lamprey) were purified by reversed-phase high-performance liquid chromatography and characterized by Edman degradation. The primary structure of a cysteine- and arginine-rich peptide (termed lamprey corticostatin-related peptide [LCRP]) was established as Cys-Pro-Cys-Gly-Arg-Arg-Arg-Cys-Cys-Val-Arg-Gly-Leu-Asn-Val-Tyr-Cys-Cys- Phe. Mass spectrometry indicated that all cysteine residues are intramolecularly linked. This amino acid sequence shows structural similarity to rat corticostatin R4 and rabbit corticostatin R1. In particular, LCRP contains the polyarginine sequence at the N-terminus of the peptide that is believed to mediate both the inhibition of ACTH stimulated steroidogenesis and the antimicrobial (defensin-like) actions of the corricostatins.

Characterization of the pancreatic hormones from the Brockmann body of the tilapia: implications for islet xenograft studies

The Brockmann body of the teleost fish, the tilapia (Oreochromis nilotica) has been considered as a potential source of islet xenograft tissue for patients with insulin-dependent diabetes. This study describes the purification from an extract of tilapia Brockmann bodies of insulin and several peptides arising from different pathways of post-translational processing of two proglucagons, two prosomatostatins and proPYY. The primary structure of tilapia insulin is similar to insulins from other teleosts (particularly the anglerfish, Lophius americanus) except that the strongly conserved glutamine residue at position 5 in the A-chain, a residue that is important in the binding of insulin to its receptor, is replaced by glutamic acid. In common with other teleosts, the tilapia Brockmann body expresses two non-allelic glucagon genes. Alternative pathways of post-translational processing lead to glucagons with 29 and 36 amino acid residues derived from proglucagon I and glucagons with 29 and 32 residues derived from proglucagon II. Glucagon-like peptides with 30 and 34 residues derived from proglucagon II were also isolated. In each case, the longer peptide is a C-terminally extended form of the shorter. Tilapia peptide tyrosine-tyrosine (PYY) was isolated in a C-terminally alpha-amidated from with 36 amino acid residues that is structurally similar (89% sequence identity) to anglerfish PYY. A 30-amino acid peptide, representing the C-terminal flanking peptide of PYY, was also isolated that shows only 53% sequence identity with the corresponding anglerfish peptide. Tilapia somatostatin-14 is identical to mammalian somatostatin but the [Tyr7, Gly10] somatostatin-containing peptide derived from prosomatostatin II contains the additional substitution (Phe11-->Leu) compared with the corresponding peptide from other teleosts.

Purification and structural characterization of insulin from a caecilian, Typhlonectes natans (Amphibia: Gymnophiona)

Despite the important position of amphibia in phylogeny, efforts at the structural characterization of amphibian neurohormonal peptides have largely been confined to the Anurans (frogs and toads). Insulin was purified from an extract of the pancreas of the caecilian, Typhlonectes natans. The primary structure of the peptide was established as: [formula: see text] This amino acid sequence contains several unusual substitutions (Gln-->Lys at A5, His-->Leu at A8, Gln-->Glu at A15, and Gly -->Ala at B20) that are not present in other amphibian insulins. The structure of insulin appears to be less well conserved among the different orders of amphibia, compared with reptiles and birds.

Characterization of insulins and proglucagon-derived peptides from a phylogenetically ancient fish, the paddlefish (Polyodon spathula)

The North American paddlefish, Polyodon spathula (Order Acipenseriformes) is an extant representative of a group of primitive Actinopterygian (ray-finned) fish that probably shared a common ancestor with present-day teleosts. Two molecular forms of insulin which differ by a single amino acid substitution, His or Asp at position 15 of the A chain, were isolated from the pancreas of the paddlefish. Paddlefish insulins show greatest structural similarity to insulin from the garfish (order Lepisosteiformes) and resemble mammalian insulins more strongly than do insulins from teleost fish. The primary structures of several proglucagon-derived peptides, two molecular forms of glucagon which differ by the single amino acid substitution Arg18-->Ser, and glucagon-like peptide, have been less well conserved during evolution. The paddlefish glucagons contain 31 amino acid residues, rather than the usual 29, and show several structural features, such as Met5, Glu24 and Gly29, not previously observed in glucagons from other species. In spite of considerable differences in structure between paddlefish and mammalian glucagons (10 or 11 amino acid substitutions), both paddlefish glucagons are equally as effective as bovine glucagon in stimulating glycogenolysis in dispersed hepatocytes from the teleost fish Sebastes caurinus (rockfish). However, the substitution Arg18-->Ser in the paddlefish glucagon results in a 6-fold decrease in potency in this system.

Recombinant coho salmon insulin-like growth factor I. Expression in Escherichia coli, purification and characterization

Recombinant coho salmon insulin-like growth factor I (rsIGF-I) was produced in Escherichia coli, purified and characterized. The rsIGF-I expression vector was constructed by polymerase chain reaction and cloning into a plasmid containing a phage T7 RNA polymerase promoter. The rsIGF-I was recovered from bacterial inclusion bodies, solubilized under reducing conditions, immediately refolded, then fractionated by a two-step ion-exchange chromatography on DEAE-52 and Mono-S columns. It was further purified by HPLC on a reverse-phase Asahi-Pak C4P-50 C4 column. Purification of rsIGF-I was monitored by SDS/PAGE and immunoblot with anti-[human somatomedin C (SM C)/IGF-I] serum. The rsIGF-I appeared as a single band with molecular mass of 7 kDa, the same size as recombinant human IGF-I (rhIGF-I) and cross-reacted with anti-(human SM C/IGF-I) serum. The amino acid sequence of rsIGF-I contained an NH2-terminal methionine residue followed by the sequence predicted for mature sIGF-I. At concentrations in the range 3.9-250 ng/ml, rsIGF-I significantly stimulated sulfate uptake by the cultured branchial cartilage of coho salmon. The stimulatory effect of rsIGF-I was concentration dependent and slightly more potent than that of rhIGF-I at the highest concentration tested.

Structure and biological activity of glucagon and glucagon-like peptide from a primitive bony fish, the bowfin (Amia calva)

The bowfin, Amia calva (order Amiiformes) occupies an important position in phylogeny as a surviving representative of a group of primitive ray-finned fishes from which the present-day teleosts may have evolved. Glucagon and glucagon-like peptide (GLP) were isolated from an extract of bowfin pancreas and their primary structures determined. Bowfin glucagon shows only four amino acid substitutions compared with human glucagon, and bowfin glucagon was equipotent and equally effective as human glucagon in stimulation of glycogenolysis in dispersed hepatocytes from a teleost fish, the copper rockfish, Sebastes caurinus. In contrast, bowfin GLP shows 15 amino acid substitutions and three amino acid deletions compared with the corresponding region of human GLP-1-(7-37)-peptide. In particular, the bowfin peptide contains an N-terminal tyrosine residue rather than the N-terminal histidine residue found in all other glucagon-related peptides so far characterized. Bowfin GLP stimulated glycogenolysis in rockfish hepatocytes, but was 3-fold less effective and 23-fold less potent than human GLP-1-(7-37)-peptide. We speculate that selective mutations in the GLP domain of bowfin preproglucagon may be an adaptive response to the previously demonstrated low biological potency of bowfin insulin.

Prosomatostatin-I is processed to somatostatin-26 and somatostatin-14 in the pancreas of the bowfin, Amia calva

With the exception of the Agnatha (lampreys and hagfishes), somatostatin-14 is the predominant molecular form of somatostatin in the pancreas of species from all classes of vertebrates yet studied. The pancreas of the holostean fish, Amia calva (bowfin; order Amiiformes) contained somatostatin-like immunoreactivity that was resolved by reversed phase HPLC in two components. The primary structure of the more abundant peptide (somatostatin-26) was established as: Ser-Ala-Asn-Pro-Ala5-Leu-Ala-Pro-Arg-Glu10-Arg-Lys-Ala-Gly-+ ++Cys15-Lys-Asn-Phe- Phe-Trp20-Lys-Thr-Phe-Thr-Ser25-Cys. This amino acid sequence shows one substitution (Leu for Met at position 6) and two deletions compared with mammalian somatostatin-28. The minor component was identical to somatostatin-14. The data show that the pathway of post-translational processing of prosomatostatin-I in the bowfin pancreas is appreciably different from the corresponding pathway in teleost fish and higher vertebrates.