title: The structure of Mordacia mordax insulin supports the monophyly of the Petromyzontiformes and an ancient divergence of Mordaciidae and Geotriidae.
abstract: The phylogenetic relationships between the two southern hemisphere lamprey families (Geotriidae and Mordaciidae) and their northern hemisphere counterparts (Petromyzontidae) are unresolved. Insulin was isolated from an extract of islet-containing intestinal tissue from ammocoetes of the Australian lamprey, Mordacia mordax. Its primary structure was established as A-chain: GIVEQCCHRK10CSIYDMENYC20N and B-chain: SALMGTGGTH10LCGSHLVEAL20YVVCGQRGFF30 YTP[SKG]. Although the residues in parentheses are only tentatively assigned, mass spectrometry supports the proposed sequence and demonstrates that Mordacia proinsulin, unlike proinsulin from Geotria australis, is fully processed to mature insulin. Insulins from M. mordax and G. australis and from the northern hemisphere lampreys Petromyzon marinus and Lampetra fluviatilis share a pentapeptide extension to N-terminus of the B-chain (Ser-Ala-Leu-Xaa-Gly) that has never been found in the insulins of any other vertebrate class. This observation provides support for the claim that the Petromyzontiformes constitute a monophyletic group. M. mordax insulin differs from that of G. australis by 18 amino acid residues but by only four residues from the common sequence of P. marinus and L. fluviatilis insulin. These data are consistent with the view that Geotriidae and Mordaciidae have been separated for a long period and suggest that G. australis insulin has undergone an accelerated rate of molecular evolution.
authors.affiliation: Regulatory Peptide Center, Department of Biomedical Sciences, Creighton University, Omaha, NE 68178, USA. jmconlon@creghton.edu
authors.forename: J M
authors.initials: JM
authors.lastname: Conlon
authors.forename: Y
authors.initials: Y
authors.lastname: Wang
authors.forename: I C
authors.initials: IC
authors.lastname: Potter
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D019143:Evolution, Molecular; D007328:Insulin / Q000737:chemistry*; D007798:Lampreys / Q000145:classification* / Q000378:metabolism*; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D010802:Phylogeny; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D013997:Time Factors
chemical_list: D007328:Insulin