Amino acid sequence of a new type of antifreeze protein, from the longhorn sculpin Myoxocephalus octodecimspinosis.
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A new type of fish antifreeze protein, designated here type IV, has been isolated from the longhorn sculpin, Myoxocephalus octodecimspinosis. Sequence analysis of the protein (LS-12) reveals that it contains 108 amino acids, is blocked at the N-terminus by a pyroglutamyl group and has a high (17%) content of glutamine; it is thus completely unrelated to the earlier described types I, II and III fish antifreeze proteins. Circular dichroism spectra and conformational analysis based on the sequence data indicate that LS-12 has a high helix content and probably folds as a four-helix bundle. LS-12 shows sequence similarity to certain plasma apolipoproteins known to have helix bundle structures, suggesting the possibility that LS-12 may have arisen by recruitment and mutation of a plasma apolipoprotein. (+info)
Cloning and sequencing of cDNA encoding the LS-12 antifreeze protein in the longhorn sculpin, Myoxocephalus octodecimspinosis.
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cDNA coding for an antifreeze protein (LS-12) in the longhorn sculpin, Myoxocephalus octodecimspinosis, was prepared from liver mRNA using reverse transcriptase-polymerase chain reaction coupled with 3' and 5' RACE procedures. This cDNA contains 609 base pairs, including a 384-bp open reading frame which codes for a 128-residue LS-12 precursor protein. The predicted amino acid sequence of the mature LS-12 corresponds exactly to the amino acid sequence obtained from Edman degradation [G. Deng, D.W. Andrews, R.A. Laursen, FEBS Lett., 402, 1997, pp. 17-20]. The 20 residues preceding mature LS-12 are predicted to be a signal sequence, which is presumably cleaved off before the mature, 108-residue protein is secreted into the circulatory system. This is the first report of a cDNA sequence from M. octodecimspinosis. (+info)
Isolation and characterization of an antifreeze protein from the longhorn sculpin, Myoxocephalus octodecimspinosis.
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A new type of antifreeze protein was isolated from the serum of the longhorn sculpin, Myoxocephalus octodecimspinosis, by gel filtration and high-performance liquid chromatography. This protein (LS-12) exhibits freezing point depression activity (thermal hysteresis) and ice crystal modification properties similar to those seen for other types of fish antifreeze polypeptide, except that ice crystals grow as hexagonal trapezohedra in the presence of LS-12, rather than hexagonal bipyramids usually seen. Ice crystal etching studies demonstrate that LS-12 does not bind to the hexagonal bipyramidal or secondary prism surfaces reported for the antifreeze polypeptides from winter flounder and shorthorn sculpin, respectively. Circular dichroism studies indicate that LS-12 has an alpha-helix content of about 60% at 1 degreesC, which is in good agreement with a value of about 70% predicted from the amino acid sequence. Limited proteolysis studies and further analysis of the amino acid sequence suggest that LS-12 consists of four amphipathic alpha-helices of similar length which are folded into a four-helix bundle. Based on its size (Mr=12299) and predicted tertiary structure, LS-12 can be regarded as the first example of a new class (type IV) of fish antifreeze protein. (+info)