Structure of a peptide antifreeze and mechanism of adsorption to ice

DNA sequence coding for an antifreeze protein precursor from winter flounder

A cDNA made to antifreeze protein mRNA of the winter flounder was cloned in the plasmid pBR322 and its sequence was determined by the method of Maxam and Gilbert. Its sequence codes for a precursor protein that is 82 amino acids in length. This precursor has both a signal polypeptide and a prosequence before the mature protein of 38 amino acid residues. The mature protein matches in composition one of the alanine-rich serum antifreeze proteins that was purified by ion-exchange and reverse-phase chromatography. The composition of the pro- sequence is similar to that of the native protein except that it contains five prolines. The mature protein, but not the pro- sequence, contains three of the 11-residue repeats previously observed [Lin, Y. & Gross, J. K. (1981) Proc. Natl. Acad. Sci. USA 78, 2825-2829] in two other antifreeze protein components.

Molecular cloning and characterization of winter flounder antifreeze cDNA

Double-stranded cDNA was synthesized from partially purified winter flounder antifreeze mRNA and inserted into the endonuclease Pst I site of plasmid pBR322 by the poly(dG).poly(dC) homopolymer extension technique. The recombinant plasmids wee used to transform Escherichia coli. Clones containing antifreeze cDNA inserts were identified by the hybridization-selection technique. One of the inserts, 380 nucleotides in length, was digested with endonucleases Sau3AI and HinfI, which cleaved the insert into three fragments. The nucleotide sequences of these fragments were determined. The cDNA contains the entire coding sequence for a possible antifreeze peptide, including the leader sequence. The predicted amino acid sequence is similar to but not identical to one of the known sequences of antifreeze peptide. Within the cDNA are three segments of repeating sequences. The basic repeating sequence of 11 amino acids is maintained in the amino acid sequence coded by the cDNA and in the antifreeze peptide.

Purification and characterization of winter flounder antifreeze peptide messenger ribonucleic acid

The serum of winter flounder contains a group of small antifreeze peptides which lower the freezing point of their body fluids during the winter months. The poly(A)-containing mRNA coding for these peptides has been isolated from livers of the winter specimens. When the isolated antifreeze mRNA was analyzed by a denaturing polyacrylamide gel electrophoresis, at least two distinct bands approximately 450 nucleotides in length are visible. In a wheat germ cell-free protein synthetic system these mRNAs direct the synthesis of small peptides which can be precipitated by antisera against purified winter flounder antifreeze peptides. Full-length cDNA was synthesized from the isolated antifreeze mRNA by avian myeloblastosis reverse transcriptase. From the RNA excess hybridization kinetic analysis, there are probably three different mRNAs coding for the antifreeze peptides. Using the radioactive cDNA probe, it was estimated that 1% of the total RNA in liver of a January specimen is antifreeze mRNA. RNA from a summar specimen showed no significant hybridization even at high concentrations of RNA. These results indicate that the control of antifreeze peptide biosynthesis relies at least in part on the synthesis or degradation of translatable mRNA.

Reverse turns in peptides and proteins

The evidence that reverse turns frequently occur as structural components of proteins, as well as of linear and cyclic peptides, is overwhelming. This review summarizes and examines critically the experimental evidence derived from physical methods such as 1H and 13C nuclear magnetic resonance spectroscopy, spin-lattice relaxation time, circular dichroism, IR spectroscopy, and X-ray crystallography. Secondly, theoretical evidence obtained from energy calculations, which rely on empirical energy functions, and correlative methods, which rely on algorithms based on the frequency of occurrence of amino acids, is evaluated. In particular, those theoretical studies for which complementary physical studies have been completed are emphasized. Finally, examples of structure-function relationships involving reverse turns and their biological recognition are demonstrated.

Renal conservation of antifreeze peptide in Antarctic eelpout, Rhigophila dearborni

In Antarctic notothenioid fishes large amounts (3% w/v) of small molecular weights of 2,600-23,500 and would be expected to be filtered into the urine, they remain in the blood because the kidneys of these fishes contain only aglomerular nephrons. Unlike the situation in most fishes, urine formation is the result of secretion rather than filtration and reabsorption. On the other hand, the peptide antifreezes in Northern Hemisphere fishes such as the winter flounder. Pseudopleuronectes americanus, are retained by the glomerular kidney even though inulin, of comparable weight, is rapidly filtered from the blood into the urine. The Antarctic eelpout (zoarcid), Rhigophila dearborni, which is unrelated to either the Antarctic notothenioids or P. americanus, also uses a peptide antifreeze (molecular weight 6,000) which is maintained at a concentration of 3% (w/v) in the blood plasma. We report here that the lack of antifreeze in the urine of R. dearborni probably reflects the fact that the glomeruli are not functional and cannot filter. We support this conclusion with morphological and physiological evidence and relate our findings to the conservation of biological antifreeze necessary for life in ice-laden polar waters.

High affinity calcium binding peptides from the gills, gut and kidneys of the freshwater eel (Anguilla anguilla)

We report the isolation of high affinity calcium-binding peptides from homogenates of gills, gut and kidneys of the freshwater eel Anguilla anguilla. These peptides show identical gel-filtration profiles on Biogel P-6, from which a molecular weight of 3500 was estimated. The average binding constant (Kf) for calcium is 7 . 10(7)M-1, and MgCl2 up to 5 mM does not displace calcium.