Chemical characterization of recombinant human leukocyte interferon A using fast atom bombardment mass spectrometry

Proteolytic digests of biologically active fractions of recombinant human leukocyte interferon A expressed in large quantities in Escherichia coli were analyzed by fast atom bombardment mass spectrometry and high-performance liquid chromatography. The values observed in the mass spectra of digests of the major fraction of recombinant human leukocyte interferon A with trypsin and Staphylococcus aureus protease V8 accounted for 93% of the amino acid sequences of human leukocyte interferon A predicted from the nucleotide sequence of the gene encoding the protein, indicating that the major fraction of recombinant human leukocyte interferon A was expressed with the same amino acid sequence as that translated from the nucleotide sequence of the gene encoding the protein. Mass spectrometry of proteolytic digests of two minor fractions of recombinant human leukocyte interferon A and mass and amino acid analyses of their high-performance liquid chromatography fractions showed that the amino group of the N-terminal amino acid residue of interferon was in part acetylated, and the Cys-1 and Cys-98 residues were oxidized to cysteic acid or linked to glutathione. These findings suggest that amino acid residues in recombinant proteins prepared in large quantities in E. coli are modified post-translationally.     

Carboxyl methylation and farnesylation of transducin gamma-subunit synergistically enhance its coupling with metarhodopsin II.

A heterotrimeric G-protein in vertebrate photoreceptor cells is called transducin (T alpha beta gamma), whose gamma-subunit is a mixture of two components, T gamma-1 and T gamma-2. T gamma-2 is S-farnesylated and partly carboxyl methylated at the C-terminal cysteine residue, whereas T gamma-1 lacks the modified cysteine residue. To elucidate the physiological significance of the double modifications in T gamma, we established a simple chromatographic procedure to isolate T gamma-1, methylated T gamma-2 and non-methylated T gamma-2 on a reversed phase column. Taking advantage of the high and reproducible yield of T gamma from the column, we analyzed the composition of T gamma subspecies in the T alpha-T beta gamma complex which did not bind with transducin-depleted rod outer segment membranes containing metarhodopsin II. The binding of T alpha-T beta gamma with the membranes was shown to require the S-farnesylated cysteine residue of T gamma, whose methylation further enhanced the binding. This synergistic effect was not evident when T alpha was either absent or converted to the GTP-bound form which is known to dissociate from T beta gamma. Thus we concluded that a formation of the ternary complex, T alpha-T beta gamma-metarhodopsin II, is enhanced by the farnesylation and methylation of T gamma. This suggests that the double modifications provide most efficient signal transduction in photoreceptor cells.     

A new trisaccharide sugar chain linked to a serine residue in bovine blood coagulation factors VII and IX

A new trisaccharide sugar chain was identified in bovine blood coagulation factors VII and IX. A pentapeptide isolated from factor VII contained Ser-52, which could not be identified with a gas-phase sequencer, suggesting an unknown substituent on the serine residue (Takeya, H. et al. (1988) J. Biol. Chem., in press). The same results were obtained for a pentapeptide containing Ser-53 of factor IX. Component sugar analysis revealed that the peptide contained 1 mol of glucose and 2 mol of xylose. This sugar component was also confirmed by high-resolution fast atom bombardment mass spectrometric analysis of the pentapeptide. The trisaccharide was released from the peptides by means of beta-elimination reaction and its reducing end was coupled with 2-aminopyridine. The fluorescent pyridylamino (PA-) derivative of the trisaccharide was purified by gel-filtration and reversed-phase HPLC. The sugar composition of the PA-trisaccharide was found to be 2 mol of xylose and 1 mol of PA-glucose. These results indicate the existence of a (Xyl2)Glc-Ser structure in factors VII and IX.     

A new type of mitogenic factor produced by Streptococcus pyogenes.

A new type of mitogenic factor (protein) was purified from the culture supernatant of a strain of Streptococcus pyogenes by SP-Sephadex C-25 column chromatography, preparative isoelectric focusing and reversed-phase high-performance liquid chromatography. The purified factor, showing marked mitogenic activity in rabbit peripheral blood lymphocytes, gave a single-band staining for protein on SDS-PAGE. The molecular weight of the purified mitogenic factor was determined to be 25,370, which was different from those calculated from reported amino acid sequences deduced from 4 different nucleotide sequences of 3 kinds of streptococcal pyrogenic exotoxins (two SPEAs, SPEB and SPEC). The amino acid sequence of the N-terminal region of the purified mitogenic factor was determined to be Gln-Thr-Gln-Val-Ser-Asn-Asp-Val-Val-Leu-Asn-Asp-Gly-Ala-Ser-Lys-Tyr-Leu- Asn-Glu - Ala-, which was also different from the reported N-terminal sequences deduced from the 4 different nucleotide sequences. These data indicate that this mitogenic factor is distinct from the already described streptococcal pyrogenic exotoxins.     

Identification of a novel amino acid, o-bromo-L-phenylalanine, in egg-associated peptides that activate spermatozoa

Eight sperm-activating peptides containing a novel amino acid were isolated from the egg jelly of the sea urchin Tripneustes gratilla. Accurate mass measurement of the peptide in FAB mass spectrometry showed that the mass of the novel amino acid residue was 224.978. On the basis of the isotopic ion distribution and the degree of unsaturation, the mass value indicated that the elemental composition of the amino acid residue was C9H8O1N1Br1, suggesting that the novel amino acid was bromophenylalanine. Proton NMR spectroscopy, amino acid analysis, and RP-HPLC with three synthetic isomers of bromophenylalanine demonstrated that o-bromophenylalanine was the novel amino acid. Derivatization of the amino acid with Marfey's reagent, (1-fluoro-2,4-dinitrophen-5-yl)-L-alanine amide (FDAA), further indicated that the amino acid was the L-isomer. In other sperm-activating peptides isolated from the egg jelly of the sea urchin, both m- and p-bromophenylalanines were discovered. The presence of m-bromophenylalanine has not been previously reported in natural products, while p-bromophenylalanine is found in theonellamide F, an antifungal bicyclic peptide from a marine sponge.     

Binding properties of monoclonal antibody to the cytoplasmic domain of transferrin receptor

Hybridomas secreting monoclonal antibodies to transferrin receptor (TFR) were isolated. One of these antibodies, U-1, recognized the cytoplasmic domain of TFR and the others, N-2 and W-3, recognized its cell surface domains. Only antibody W-3 competed with transferrin (TF) for binding to TFR. Antibody U-1 bound to purified TFR but not to 35S- or 125I-TFR in cell extracts. 125I-Antibody U-1 bound to TFR alone in cell extracts when TFR was bound to antibody N-2-Sepharose 4B, but even in the presense of cell extracts it did not bind to TFR bound to antibody W-3-Sepharose 4B. Antibody W-3 co-precipitated TFR and a protein of about 30 kDa from cell extracts, and also reacted with the 30 kDa protein in cell extracts in the absence of TFR. Based on these results, the existence of two different states of the cytoplasmic domain of TFR is discussed.     

Purification and characterization of a heat-stable enterotoxin of Vibrio mimicus

A heat-stable enterotoxin produced by Vibrio mimicus (VM-ST) was studied. VM-ST was purified from a culture supernatant of V. mimicus strain AQ-0915 by ammonium sulfate fractionation, hydroxyapatite treatment, ethanol extraction, column chromatography on both SP-Sephadex C-50 and DEAE-Sephadex A-25, and HPLC, and the recovery rate was about 15%. Purified VM-ST was heat-stable. VM-ST activity was cross-neutralized by anti-STh antiserum. The amino acid composition of the purified VM-ST was determined 17 amino acid residues in the following sequence: Ile-Asp-Cys-Cys-Glu-Ile-Cys-Cys-Asn-Pro-Ala-Cys-Phe-Gly-Cys-Leu-Asn. This composition and sequence were identical to those of V. cholerae non-O1-ST. These results clearly demonstrate the production of a characteristic VM-ST by V. mimicus.     

Isolation and characterization of four VIP-related peptides from red-bellied newt, Cynops pyrrhogaster

Four novel bioactive peptides were isolated from the red-bellied newt, Cynops pyrrhogaster, using a bioassay system monitoring the rectum contraction of the Japanese quail, Coturnix japonica. As these peptides are structurally related to vasoactive intestinal polypeptide (VIP), we termed these peptides newt VIP-related peptides 1, 2, 3, and 4 (NVRP-1, -2, -3, and -4). The primary sequences of these peptides were determined to be HSDAVFTDNYSRLLGKTALKNYLDGALKKE (NVRP-1), HSDAVFTDNYSRLLAKTALKNYLDGALKKE (NVRP-2), HSDAVFT-DNYSRLLGKIALKNYLDEALKKE (NVRP-3), and HSDAVFTDNYSRLLGKT-ALKNYLDSALKKE (NVRP-4). The N-terminal regions of these NVRPs possessed homology at the amino-acid level to various VIP, while the NVRP C-termini differed from VIPs significantly. All of the VIP consist of 28 amino-acid residues with amidated forms at the C-termini, whereas NVRPs possess 30 amino-acid residues and have free forms at the C-termini. NVRPs exert relaxant activities on isolated quail rectums in a dose-dependent manner, with threshold concentrations between 1 x 10(-8) and 3 x 10(-8) M. NVRPs also exhibited potent relaxant activities acting on the newt duodenum at 3 x 10(-8) M. As yet, this is the first isolation of biologically active VIP-related peptides from urodele.     

Characterization of a solvent resistant and thermostable aminopeptidase from the hyperthermophillic bacterium, Aquifex aeolicus

A leucine aminopeptidase gene of Aquifex aeolicus, a hyperthermophilic bacterium, was cloned and expressed in Escherichia coli, and its expression product was purified and characterized. The expressed protein was purified to homogeneity by using heat to denature contaminating proteins followed by ion-exchange chromatography to purify the heat-stable product. The purified enzyme gave a single band on SDS-PAGE with a molecular weight of 54 kDa. Kinetic studies on the purified enzyme confirmed that it was a leucine aminopeptidase. The optimum temperature for its activity was around 80 degrees C and the optimum pH was in the range from 8.0 to 8.5. It was stable at high temperatures and 27% of its activity was retained after heating at 115 degrees C for 30 min. The purified enzyme had a pH stability range between 4.0 and 11.0. This aminopeptidase was highly resistant to organic solvents such as methanol, ethanol, tetrahydrofuran, dimethyl sulfoxide, acetone, acetonitrile, dimethyl formamide, 1-propanol, 2-propanol, and dioxane.