Purification and characterization of insulin from the Australian lungfish, Neoceratodus forsteri (Dipnoi)

Purification, characterization, and biological activity of a substance P-related peptide from the gut of the Australian lungfish, Neoceratodus forsteri

A peptide with mammalian substance P (SP)-like immunoreactivity was isolated from an extract of the spiral intestine of the Australian lungfish, Neoceratodus forsteri. The primary structure of this peptide was established as Lys-Pro-Arg-Pro-Asp-Glu-Phe-Tyr-Gly-Leu-Met . NH2, showing 64% identity with mammalian SP. In isolated preparations of lungfish foregut circular muscle, lungfish SP produced a slow, long-lasting tonic contraction, with a pD2 value of 8.19. Lungfish midgut circular muscle preparations responded to lungfish SP rapidly and in a more complex manner. There was an increase in the frequency of spontaneous activity (pD2 = 8.76), associated with diminished amplitude of the spontaneous contractions (pD2 = 9.24), also coupled in some preparations with a tonic contraction (pD2 = 8.43). The response patterns of foregut and midgut circular muscle to acetylcholine (ACh) were very similar to those seen to lungfish SP. Lungfish SP and ACh, however, had very weak effects on both foregut and midgut longitudinal muscle. These data demonstrate that lungfish SP may be a physiologically important regulator of gastrointestinal motility in Neoceratodus. This study further confirmed that the structures of SP-related peptides have been strongly conserved under the pressure of vertebrate evolution, particularly in preserving the functionally important sequence, Phe-Xaa-Gly-Leu-Met . amide, at the C-terminus. The sequence of lungfish SP is identical to that of bufokinin, a SP-related peptide previously isolated from the intestine of the cane toad, Bufo marinus, supporting the hypothesis that lungfishes and amphibians share a common ancestor.

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.

Islet hormones from the African bullfrog Pyxicephalus adspersus (Anura:Ranidae): structural characterization and phylogenetic implications

The African bullfrog Pyxicephalus adspersus is generally classified along with frogs of the genus Rana in the subfamily Raninae of the family Ranidae but precise phylogenetic relationships between species are unclear. Pancreatic polypeptide (PP), insulin, and glucagon-like peptide (GLP-1) were isolated from an extract of P. adspersus pancreas and characterized structurally. A comparison of the amino acid sequence of Pyxicephalus PP (APSEPQHPGG(10)QATPEQLAQY(20)YSDLYQYITF(30)ITRPRF++ +. NH(2)) with those of the known amphibian PP molecules in a maximum parsimony analysis generates a single phylogenetic tree in which Pyxicephalus is the sister to the clade comprising the members of the genus Rana. The three orders of living amphibians form discrete clades with the representative of the Gymnophiona appearing as sister to the Caudata-Anura. In contrast, Pyxicephalus insulin (A chain, GIVEQCCHSA(10)CSLYDLENYC(20)N; B-chain, LANQHLCGSH(10)LVEALYMVCG(20)ERGFFYYPKS(30)) and and GLP-1 (HAEGTFTSDM(10)TSYLEEKAAK(20)EFVDWLIKGR(30)PK) resemble more closely the corresponding peptides from the cane toad Bufo marinus than the peptides from any species of Rana. Cladistic analysis based upon the amino acid sequences of insulin produced a polyphyletic assemblage with the Gymnophiona nesting within an unresolved clade containing the non-ranid frogs. The data support the assertion that the amino acid sequence of PP, but not those of the other islet hormones, is of value as a molecular marker for inferring phylogenetic relationships between early tetrapod species.

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.