Purification of human leukocyte interferon A derived from Escherichia coli: An aging process to prevent the formation of its oligomers

Introduction of a non-native disulfide bridge to human lysozyme by cysteine scanning mutagenesis

To examine whether the disulfide bridge between residues 65 and 81 can be replaced by a non-native disulfide bridge in the mutant h-lysozyme C77/95A and whether the formation of such a new disulfide bridge affects the folding of the protein, cysteine scanning mutagenesis has been performed within two discontinuous segments (residues 61-67 for the mutant C65/77/95A, and 74-84 for the mutant C77/81/95A). The position of the Cys residue at 65 or 81 was continuously shifted by site-directed mutagenesis. Of the mutants, only substitution of Cys for Trp64 allowed the secretion of mutant h-lysozyme(W64C) into the medium in a sufficient amount for analysis. After the purification, the mutant enzyme was obtained as two components (W64C-A and W64C-B). The only difference between A and B was that A had a peptide bond cleaved between Ala77 and His78. A non-native disulfide bridge between residues 64-81 was found in both components. Little difference was observed in CD spectra among wild-type and mutant enzymes. It is likely that the tertiary structure of the W64C mutant might be distorted at the location, because the directions of amino acid side chains at positions of 64 and 81 are shown to be opposite to each other in wild-type h-lysozyme by X-ray crystallographic analysis.

Analysis of post-translational modifications of proteins by accurate mass measurement in fast atom bombardment mass spectrometry

A rotatable dual-target probe was used for accurate mass measurement in fast atom bombardment mass spectrometry to determine the structures of unknown amino acid residues or post-translationally modified structures in peptides or proteins. The results obtained in measurement of tryptic peptides (with molecular weights of up to 2000) of the A-subunit of vero-toxin I indicated that the mass values obtained are sufficiently accurate and reproducible to allow the generation of the possible elemental compositions for modifications in peptides. By this method, the structural modifications of the N-terminal of a recombinant human leukocyte interferon A and novel halogenated amino acids in sperm-activating peptides from the egg-jelly of sea urchins were determined.

Direct amino acid analysis of proteins electroblotted onto polyvinylidene difluoride membrane from sodium dodecyl sulfate-polyacrylamide gel

The band of appropriate proteins (basic pancreatic trypsin inhibitor, soybean trypsin inhibitor, interleukin 2, and human leukocyte interferon alpha A) on a polyvinylidene difluoride (PVDF) membrane, which was electroblotted from sodium dodecyl sulfate (SDS)-polyacrylamide gel and then stained with Coomassie blue R-250, was cut out and directly hydrolyzed in HCl in the presence of thioglycolic acid for amino acid analysis. The analytical values agreed with those expected with recoveries of 29-47%, except that the value for tryptophan was very low or scarcely detected. This method was applied to the identification of human growth hormone (hGH) in a partially purified preparation. The amino acid composition of the band corresponding to about 2 micrograms of hGH agreed with the theoretical values. These results indicate that the band on the PVDF membrane can be directly hydrolyzed for amino acid analysis and that the method can be used for partially purified proteins separated using SDS-polyacrylamide gel electrophoresis.

Escherichia coli-derived human interferon-gamma with Cys-Tyr-Cys at the N-terminus is partially N alpha-acylated

Purified preparations of recombinant human interferon-gamma (rIFN-gamma) with Cys-Tyr-Cys at the N-terminus ([ Cys-Tyr-Cys]IFN-gamma) derived from Escherichia coli gave two closely migrating bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and two peaks on reversed-phase high-performance liquid chromatography (rpHPLC). In contrast, rIFN-gamma without Cys-Tyr-Cys and rIFN-gamma in which both Cys-1 and Cys-3 were substituted with serine behaved as a single species on both SDS-PAGE and rpHPLC. These results suggest that the N-terminal portion of rIFN-gamma is heterogeneous. To elucidate the structure of the N-terminal portion, the N-terminal peptide preparation was obtained by binding rIFN-gamma to thiopropyl-Sepharose 6B gel with disulfide linkage followed by trypsin digestion and elution with 2-mercaptoethanol. The preparation gave four peaks (NT-1, NT-2, NT-3, and NT-4, in order of elution) on rpHPLC; all four were found to be Cys-1-Lys-9 by amino acid analysis after acid hydrolysis. Various analyses indicate that NT-1 is the intact nonapeptide, that NT-3 and NT-4 are N alpha-formyl and N alpha-acetyl forms of NT-1, respectively, and that NT-2 may be S-blocked at Cys-1. It is concluded that E. coli-derived [Cys-Tyr-Cys]IFN-gamma is partially N alpha-acylated. The data also suggest that N alpha-acylation does not affect the biological activity of [Cys-Tyr-Cys]IFN-gamma.

Characterization of three species of Escherichia coli-derived human leukocyte interferon A separated by reverse-phase high-performance liquid chromatography

A preparation of recombinant human leukocyte interferon A (rIFN-alpha A) obtained from Escherichia coli cells was found by reverse-phase high-performance liquid chromatography (HPLC) to contain three species. The three species, named Mf-1, Mf-2, and Ms in the order of their elution, were separated and characterized to elucidate their structural differences. The amino acid compositions, the amino-terminal amino acid sequences (Cys1-Asp2-Leu3-), and the carboxy-terminal amino acids (Glu) of the three species agreed with those predicted from the cDNA sequence, although the sequence analysis yields of Mf-2 and Ms were extremely low. They were found to have the same disulfide bonds, Cys1-Cys98 and Cys29-Cys138, by amino acid analysis of the tryptic peptides, but the recovery of the peptides linked by a Cys1-Cys98 disulfide bond for Mf-2 and Ms was extremely low. The results demonstrate that although the primary structures of the three species are almost identical, small difference(s) exists among them especially at the amino-terminal portion.