Separation of various calmodulins, calmodulin tryptic fragments, and different homologous Ca2+-binding proteins by reversed-phase, hydrophobic interaction, and ion-exchange high-performance liquid chromatography techniques

Soluble calcium-binding proteins: parvalbumins and calmodulin from eel skeletal muscle

1. Eel skeletal muscle contains three parvalbumin isoforms. The overall parvalbumin concentration in the muscle is 0.5 mmol kg-1 wet weight. 2. Calmodulin (0.1 mumol kg-1 wet weight) was purified by extraction with ethylenediamine tetraacetate-containing buffer, fractionation with trichloroacetic acid and separation by ion exchange chromatography on DEAE-cellulose and by molecular sieving on Ultrogel AcA 54. 3. Troponin-C-free calmodulin was obtained by fast protein liquid chromatography on a Mono Q column.

Hydrophobic interaction chromatography of peptides as an alternative to reversed-phase chromatography

Hydrophobic interaction chromatography (HIC) was examined as an alternative to reversed-phase chromatography (RPC) for peptide separations by high-performance liquid chromatography. With small peptides, selectivity was similar in both modes. This was the case with commercially available standards and with a set of synthetic peptides having the same amino acid composition but different sequences. Column efficiency was higher in RPC. HIC possesses several other disadvantages, including significant baseline changes during gradient elution and a requirement for non-volatile mobile phases, which complicates peptide isolation. Thus, RPC is still the method of choice for most small peptides. Marked differences in selectivity were noted with small proteins and polypeptides large enough to possess tertiary structure. Good results were also obtained by HIC in the case of some peptides that could not be purified at all by RPC, due to aggregation or poor binding or recovery. Thus, in these cases, HIC is a useful alternative to RPC for peptide purification.

Cation-exchange chromatography of peptides on poly(2-sulfoethyl aspartamide)-silica

A strong cation-exchange material, poly(2-sulfoethyl aspartamide)-silica (PolySULFOETHYL Aspartamide) was developed for purification and analysis of peptides by high-performance liquid chromatography. All peptides examined were retained at pH 3, even when the amino terminus was the only basic group. Peptides were eluted in order of increasing number of basic residues with a salt gradient. Capacity was high, as was selectivity and column efficiency. This new column material displays modest mixed-mode effects, allowing the resolution of peptides having identical charges at a given pH. The selectivity can be manipulated by the addition of organic solvent to the mobile phases; this increases the retention of some peptides and decreases the retention of others. The retention in any given case may reflect a combination of steric factors and non-electrostatic interactions. Selectivity was complementary to that of reversed-phase chromatography (RPC) materials. Excellent purifications were obtained by sequential use of PolySULFOETHYL Aspartamide and RPC columns for purification of peptides from crude tissue extracts. The new cation exchanger is quite promising as a supplement to RPC for general peptide chromatography.

Correlation of calcitonin structure with chromatographic retention in high-performance liquid chromatography

Chromatographic selectivity and position specificity were examined by using deletion and substitution analogues of calcitonin (CT), a 32-amino acid polypeptide. The biological activity of CT has been shown to be related to structural features, including a regular spacing of hydrophobic and hydrophilic residues in positions 8-22. The effect of structure on retention behavior in hydrophobic interaction chromatography (HIC) and reversed-phase chromatography (RPC) of 19 CT analogues was examined. No simple correlation was found between chromatographic retention and amino acid composition. Deletion of one leucine residue reduced retention in both chromatographic systems, but the magnitude of the change depended upon the site at which the deletion occurred. For example, deletion analogues des(Leu16)-, des-(Leu12)-, des(Leu10)-, des(Leu9)-, des(Leu4)-, and salmon calcitonin had retention times of 5.22, 8.44, 11.64, 13.53, 15.45, and 20.28 min, respectively, in HIC in contrast to RPC retentions of 15.19, 15.84, 28.53, 27.57, 25.92 and 34.79 min, respectively. Serine deletion was also shown to be position-specific. Non-amphiphilic analogues were eluted before amphiphilic ones. Circular dichroic spectral studies showed that the CT analogues possessed little secondary structure in the HIC solvents in contrast to alpha-helix formation in RPC solvents. The HIC data provided indirect evidence of secondary structure, induced in the amphiphilic CT analogues at the HIC solvent-chromatographic surface interface. Solute-solvent interactions contributed to differences observed between the selectivity of RPC and HIC.

Analysis of the binding of Ca2+ to gramicidin A in ethanol in terms of the dimer-monomer conformational equilibrium

This study reports the first direct observation of the binding of Ca2+ to gramicidin A in ethanol, analysed in terms of the polypeptide dimer-monomer conformational equilibrium. High performance size-exclusion chromatography has been successfully used to elucidate the binding mechanism and to determine the rate constants as well as the stoichiometry of the processes involved. In addition, fluorescence intensity and anisotropy measurements have revealed a dependence of the number of accessible Ca2+-binding sites on the peptide concentration.

Stimulation of the erythrocyte Ca2+-ATPase and of bovine brain cyclic nucleotide phosphodiesterase by chemically modified calmodulin

Chemically modified calmodulins have been used to investigate structural features which are important for the interaction of the activator with targets. Carbamoylation of lysine residues had no influence on the ability of calmodulin to stimulate the plasma membrane Ca2+-ATPase whereas the stimulation of the bovine brain cyclic-nucleotide phosphodiesterase was reduced up to 50%. Different species of carbamoylated calmodulin have been isolated but no differences were detected in their interaction with the cyclic-nucleotide phosphodiesterase. Modification of arginine residues by 1,2-cyclohexanedione had no effect of the stimulation of the phosphodiesterase but reduced by 40% the stimulation of the erythrocyte Ca2+ ATPase. Mild oxidation of methionines by N-chlorosuccinimide produced a number of differently modified calmodulins. The different species have been purified and the modified residues have been identified. They affected the two different test enzymes to different extents indicating that methionines in the central helix of calmodulin are of greater importance for the interaction with the phosphodiesterase, whereas methionines located in the C-terminal half of calmodulin are more important for the interaction with the Ca2+-ATPase.

Calmodulin-drug interaction. A fluorescence and flow dialysis study

Various Ca2+-antagonists and related compounds were probed for possible anti-calmodulin properties. Some of them efficiently inhibit calmodulin dependent activity (the plasma membrane Ca2+-ATPase and the cyclic nucleotide phosphodiesterase). The I50-values for the most potent inhibitors varied between 15 and 30 uM. Using fluorescence spectroscopy and flow dialysis methods the stoichiometry of the binding of some of the drugs to calmodulin has been investigated. The number of Ca2+-dependent high affinity binding sites has been studied on trypsin fragments of calmodulin. Compound 12-114 was bound with high affinity in a Ca2+-dependent way to both halves of calmodulin, compound 200-737 recognized one high affinity binding site only in the C-terminal half of the molecule, whereas compound 36-079 demanded the intact protein to be able to interact with high affinity in a Ca2+-dependent manner.

Effect of tryptic calmodulin fragments on guanylate cyclase activity from Paramecium tetraurelia

Tryptic bovine brain calmodulin fragments 1-77 or 1-106 reactivated La-inactivated ciliary guanylate cyclase from Paramecium dose-dependently up to 60%. They were 20-fold less potent compared to bovine brain calmodulin. Fragment 78-148 was even less active. Concomitant addition of fragments 1-77 and 78-148 had no additive effect. Genetically engineered calmodulin lacking a blocked amino terminus and trimethyllysine at position 115 reactivated La-treated guanylate cyclase as good as bovine brain calmodulin. After detergent solubilization of La-inactivated guanylate cyclase intact bovine brain calmodulin and calmodulin fragments 1-77 and 78-148 were equipotent. 80% Reactivation was obtained with 40 microM of either fragment.

Parvalbumin in cat brain: isolation, characterization, and localization

Because of the increasing evidence that Ca2+-binding proteins have important regulating functions in nerve cells and because of the indications that there are species differences in the structures of these proteins, parvalbumin was purified from cat brain and muscle. Brain and muscle parvalbumins were found to be indistinguishable from each other in their biochemical and immunological properties. However, cat parvalbumin differs from all other mammalian parvalbumins by its apparently lower Mr on sodium dodecyl sulfate-polyacrylamide gel electrophoresis of 10-11K (compared to rat parvalbumin, 12K), and a lower pI of 4.6 (rat parvalbumin, 4.9), in the tryptic peptide maps, and in the immunological properties, indicating a distinct primary structure. With the purified parvalbumin as antigen, polyclonal antibodies were raised in rabbits and these were subsequently used for immunohistochemical localizations of parvalbumin in the cat brain. In the visual cortices of adult cats immunoreactive neurons were present throughout layers II and IV. In cerebellar cortex, Purkinje, basket, and stellate cells were immunoreactive. Comparison with staining patterns obtained with antiserum against rat parvalbumin revealed some cross-reactivity but confirmed the existence of species differences in the antigenic structure of rat and cat parvalbumin.