Preparation and conformational study of clupeine fragments

Studies on the function mechanism of a Formosan grey mullet protamine-mugiline beta M6: interaction of the M6 and M6 fragments with DNA

The interaction of three peptide segments of one component of Formosan grey mullet protamine (mugiline beta M6), obtained by chemical and enzymatic cleavage, with DNA was studied by spectroscopic measurement, thermal denaturation and circular dichroism. The data obtained were then compared with those of whole M6 and other fish protamines such as salmine of salmon and clupeine of herring. M6-B-I, which lacks C-terminal 11 amino acids in M6, showed significantly different properties. It showed remarkably high DNA aggregating ability which was due to a conformational change of DNA from B to A form. The conformational change of DNA induced by the binding of M6-B-I was reproduced by the carboxypeptidase B digestion of DNA-M6 complex. From these results, the arginine-rich, C-terminal domain of the M6 molecule was estimated to be essential for natural DNA binding.

Synthetic, immunological and structural studies on repeat unit peptides of Plasmodium falciparum antigens

Using solid phase methodology, we have synthesized five peptides (16-18 residues long) corresponding to repeat sequences of four antigens of a human malarial parasite, Plasmodium falciparum. Three of these antigens (RESA, FIRA, and ABRA) are found in the asexual blood-stages of the parasite, while the remaining one (CSP) is found in the sporozoites. The synthetic peptides, conjugated to bovine serum albumin, elicited high levels of antibodies in rabbits, and these antibodies were found to cross-react with the heterologous peptides. The degree of cross-reactivity, as estimated in an ELISA, was quite remarkable among all the peptides. The peptide corresponding to the RESA tetrapeptide repeat was found to be the most immunogenic and highly cross-reactive. For this reason this tetrapeptide repeat unit, peptide 1, may be a suitable candidate for inclusion in a multiple epitope polypeptide vaccine design. Conformational studies using circular dichroism spectroscopy show that these peptides have similar conformational characteristics with a common feature of approximately 30% and approximately 50% helical content water and TFE respectively. Theoretical predictions regarding conformation using the Chou-Fasman method have also been presented.

Circular dichroism studies on synthetic peptides corresponding to the cleavage site region of precursor proteins

The conformations of synthetic peptides which span the region in which the precursor part of proteins (signal sequences) destined for export are cleaved by signal peptidases, were investigated by circular dichroism spectroscopy. Pentapeptides comprising amino acids only from the carboxy-terminus of signal sequences or the amino terminus of the mature protein do not have any preferred conformation in a variety of solvents. Octa- and nonapeptides containing amino acids from the carboxy-terminal protion of signal sequences and the amino-terminus of the mature portions of precursor proteins tend to adopt beta-turn conformations in trifluoroethanol and micelles of sodium dodecylsulphate. Hence, in addition to the distribution of amino acids with small side chains at the carboxy terminus of signal sequences, it is conceivable that signal peptidases also recognize a beta-turn conformation in the cleavage site region of precursor proteins.

Interaction of the three main components of clupeine with glycosaminoglycans

The interactions between each of the three main components of clupeine (YI, YII and Z) and the glycosaminoglycans chondroitin sulfate, heparin and hyaluronic acid were studied with circular dichroism spectroscopy. The induced dichroism is a measure of relative complex stability, which increases with the number of sulfate groups on the glycosaminoglycan. Measuring the induced dichroism as a function of mole ratio of disaccharide to arginine establishes the stoichiometry of the complexes. For a given glycosaminoglycan, the induced dichroism depends on the clupeine, increasing the order YI less than YII less than Z.