Separation of recombinant human interleukin-2 and methionyl interleukin-2 produced in Escherichia coli

Sequence specificity and efficiency of protein N-terminal methionine elimination in wheat-embryo cell-free system

Recent improvements in wheat-embryo cell-free translation resulted in a highly productive system for protein preparation. To clarify N-terminal processing of the cell-free system in a preparative-scale (> mg protein product per ml), 20 mutant variants of maltose-binding protein (MalE), each having a different penultimate residue in the sequence Met-Xaa-Ile-Glu-, and 20 glutathione S-transferase (GST) variants, having Met-Xaa-Pro-Ile-sequence, were designed and synthesized. The MalE and GST proteins were purified by amylose-resin and glutathione columns, respectively, followed by analysis of their N-terminal sequences. These investigations revealed that sequence specificity and efficiency of the N-terminal Met (N-Met) elimination in the cell-free system are similar to those reported from investigations in cellular systems or in the wheat-embryo cell-free protein expression system in analytical scale (approximately 10 microg protein product per ml). Cleavage of the N-Met is basically determined by the penultimate amino acid in the polypeptide sequence. In the case of MalE, the cleavage was efficient when the penultimate residue was Ala, Cys, Gly, Pro, Ser or Thr. But, in the case of GST with Pro as the antepenultimate residue, the efficiency was significantly reduced when the penultimate residue was Gly or Thr. We also confirmed that substitution of the antepenultimate residue in MalE to Pro drastically reduced the efficiency of N-Met cleavage when the penultimate residue was Ala, Gly, Pro, Ser or Thr, indicating inhibitory effects of antepenultimate residue Pro on N-Met elimination. These results clarified sequence-specific functions of the endogenous N-terminal processing machinery in the scaled-up wheat-embryo cell-free translation system.

The action of N-terminal acetyltransferases on yeast ribosomal proteins

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was used to determine the state of N-terminal acetylation of 68 ribosomal proteins from a normal strain of Saccharomyces cerevisiae and from the ard1-Delta, nat3-Delta, and mak3-Delta mutants (), each lacking a catalytic subunit of three different N-terminal acetyltransferases. A total 30 of the of 68 ribosomal proteins were N-terminal-acetylated, and 24 of these (80%) were NatA substrates, unacetylated in solely the ard1-Delta mutant and having mainly Ac-Ser- termini and a few with Ac-Ala- or Ac-Thr- termini. Only 4 (13%) were NatB substrates, unacetylated in solely the nat3-Delta mutant, and having Ac-Met-Asp- or Ac-Met-Glu- termini. No NatC substrates were uncovered, e.g. unacetylated in solely mak3-Delta mutants, consistent with finding that none of the ribosomal proteins had Ac-Met-Ile-, Ac-Met-Leu-, or Ac-Met-Phe- termini. Interestingly, two new types of the unusual NatD substrates were uncovered, having either Ac-Ser-Asp-Phe- or Ac-Ser-Asp-Ala- termini that were unacetylated in the ard1-Delta mutant, and only partially acetylated in the mak3-Delta mutant and, for one case, also only partially in the nat3-Delta mutant. We suggest that the acetylation of NatD substrates requires not only Ard1p and Nat1p, but also auxiliary factors that are acetylated by the Mak3p and Nat3p N-terminal acetyltransferases.

Enhancement of anti-tumor activity of recombinant interleukin-2 (rIL-2) by immunocomplexing with a monoclonal antibody against rIL-2

We have investigated biological properties of an immune complex of recombinant interleukin-2 (rIL-2) and a monoclonal antibody against rIL-2 in mice for induction of killer cells and for anti-tumor activity. We have also examined the clearance of subcutaneously-injected immune complex in mice and compared it with that of rIL-2 alone. Plasma rIL-2 levels were sustained longer in mice given the immune complex than in mice given rIL-2 alone at a dose of 10 micrograms/mouse, and they were detectable even at 24 hours after the administration of the immune complex, while they fell to undetectable levels by 6 hours after the administration of rIL-2 alone. A more significant portion of rIL-2 was detected in lymph nodes after subcutaneous injection of the immune complex than that of rIL-2 alone. Splenic lymphocytes from mice given the immune complex demonstrated a higher killer cell activity against YAC-1 cells than those from mice given rIL-2 alone. The immune complex also exerted more significant anti-tumor effect in a dose-dependent manner in Meth-A fibrosarcoma-bearing mice than rIL-2 alone. Our results indicate that immunocomplexing of rIL-2 with an antibody against rIL-2 provides a useful tool as the drug delivery system for cancer therapy using rIL-2.

Amino-terminal methionine processing of the protein HPr in Streptococcus salivarius grown in continuous culture

HPr is a protein of the phosphoenolpyruvate:sugar phosphotransferase system (PTS). Streptococci possess two forms of HPr which differ by the presence or the absence of the N-terminal methionine (Met). These forms are called HPr-1 (without Met) and HPr-2 (with Met). In order to determine whether the ratio of these two forms varies with growth conditions, we measured the amount of HPr-1 and HPr-2 present in Streptococcus salivarius grown in continuous culture at pH 7.5. The results indicated that the HPr-1/HPr-2 ratio: 1) was not related to the cellular amount of total HPr; 2) was highest (10.2 +/- 3.5) under glucose (a PTS sugar) limitation (10 mM) and low dilution rate (D = 0.1 h-1; g = 6.9 h); 3) was decreased 2.4- to 5.7-fold when the amount of glucose and/or D was increased; 4) was not influenced by D when cells were cultured on galactose (a non-PTS sugar) but was two-fold higher under conditions of galactose excess (200 mM). We suggest that the cleavage of the N-terminal HPr Met is not a stochastic phenomenon but is dictated by growth conditions.

Antitumor effect of recombinant human interleukin-2 on the growth of murine hemangioendothelioma D14 in nude mice: occurrence of large granular cells in the tumor

The antitumor effect of recombinant human interleukin-2 (rIL-2) on murine hemangioendothelioma D14 (D14) in female BALB/c-nu/nu mice was examined histologically. D14 cells which had been maintained in vitro were transplanted subcutaneously into nude mice on day 0 (1 x 10(7) cells/mouse). The mice with established tumor on day 28 received rIL-2 subcutaneously at a dose of 20 micrograms/mouse/day for 35 days. On day 63, the mice were killed, and the tumor, spleen and bone marrow were examined histologically. In the mice that had received rIL-2, tumor growth was significantly suppressed. Histologically, there was marked infiltration of large granular cells (about 15-30 microns in diameter) in the tumors. In the adjacent areas, there was a significant increase in the number of tumor cells showing karyorrhexis. The large granular cells (LGC) contained periodic acid Schiff-positive round granules in the cytoplasm and were stained positively for Thy-1.2 surface antigen. The LGC were also positive for asialo GM1 surface antigen but not for Lyt-1, Lyt-2 or IgG surface antigens. This evidence suggests that the LGC are lymphokine-activated killer-like cells which were derived from a natural killer cell lineage. The concomitant increases in the number of LGC and the number of cells showing karyorrhexis in the tumors of the mice treated with rIL-2 suggest that LGC play an important role in the destruction of tumor cells.

The effects of recombinant human granulocyte-macrophage colony-stimulating factor on the induction of lymphokine-activated killer cells in vitro

Granulocyte-macrophage colony-stimulating factor (GM-CSF) was added to a culture of human peripheral blood mononuclear cells in the presence of interleukin 2 (IL-2) in vitro to elucidate its effect on the induction of lymphokine-activated killer (LAK) cells. Viable cell counts of cultured cells and their cytotoxic effects against natural killer (NK) cell-resistant Daudi cells and NK cell-sensitive K562 cells were measured using the trypan blue dye exclusion test and a 51Cr release assay from the tumor cells, respectively. Although GM-CSF alone did not influence either the cytotoxicities or the surface phenotypes of the cultured cells, the viable cell counts were significantly increased by the addition of GM-CSF in the presence of IL-2 (P less than 0.01). These findings indicate that the addition of GM-CSF in the presence of IL-2 during the induction of LAK cells is useful for obtaining a larger number of effector cells which possess substantial cytotoxic activity.

Inhibitory effects of hepatitis B virus antigen on induction of lymphokine-activated killer cell activity

We investigated the inhibitory effects of purified recombinant hepatitis B virus (HBV) surface antigen (rHBsAg) and core antigen (rHBcAg) on lymphokine-activated killer cell (LAK) activity. Either peripheral blood mononuclear cells (PBMCs) or CD16+ CD3- LAK precursors, both of which were pre-incubated with interleukin-2 (IL-2) and rHBsAg or rHBcAg for 72 h, showed a significant decrease in LAK cytotoxicity against Daudi cells, in comparison to the results recorded in the presence of IL-2 alone, or IL-2 and E. coli extracts. This inhibitory effect was dose-dependent and was observed to be time-dependent from 24 to 72-h-cultures with these HBV antigens. This influence was not mediated with either adherent cells or other accessory cells. The proliferative reaction of either PBMCs or the LAK precursors after being cultured with IL-2 and rHBsAg or rHBcAg for 72 h was significantly diminished compared with the levels of reaction of those cells after a 72-h culture with IL-2 alone or with IL-2 and E. coli extracts. The levels of IL-2-driven IL-2 receptor (p55) expression of either PBMCs or the LAK precursors in the presence of rHBsAg or rHBcAg were higher than the levels seen in the absence of these HBV antigens. These results suggest that HBsAg and HBcAg may inhibit the induction of LAK activity by interfering with the proliferative reaction of the LAK precursors to IL-2 without inhibiting the IL-2 receptor expression of the cells. Cytofluorographic analysis of PBMCs, cultured with rIL-2, showed lower percentages of CD3+ and CD16+ cells in the presence of these HBV antigens than those in the absence of antigens.

Defective immunological functions associated with abnormal lymphokine-activated killer activity in patients with hepatocellular carcinoma

The in vitro lymphokine-activated killer (LAK) activity of peripheral blood mononuclear cells (PBMC) from 36 patients with hepatocellular carcinoma was investigated. The activity was greatly diminished in 13 patients and enhanced in seven patients. A flow cytometric study showed that the percentage of OKM1+, Leu-7+-11b+, and Leu-7-11b+ fractions in PBMC was decreased and the percentage of OKT8+ and Leu7+11- fractions was increased significantly in the 13 patients with lower LAK activity, compared with the values of the seven higher LAK activity patients. Furthermore, the response of PBMC to interleukin-2 (IL-2) was deficient in the lower activity group. However, there was no significant difference in IL-2 production by PBMC, IL-2 receptor (p55) expression of PBMC and mitogen (Con-A, PHA) response of PBMC between the two groups. These findings indicate the possibility that diminished LAK activity in hepatoma patients is due to a decreased number of LAK precursor cells and a defective response of LAK precursor cells to IL-2.

Intratumoral injection of OK432 and lymphokine-activated killer activity in peripheral blood of patients with hepatocellular carcinoma

Lymphokine-activated killer (LAK) activity of peripheral blood mononuclear cells (PBMC) from 33 patients with hepatocellular carcinoma was significantly decreased compared with that of healthy volunteers. There was less LAK activity in PBMC from patients with larger tumours (5 cm or more in diameter) than in patients with smaller tumours (under 5 cm in diameter). In 8 out of 20 patients with larger tumours there was none or little LAK activity. Flow cytometry revealed that the percentage of Leu11b+ cells in PBMC was lower in patients than in normal volunteers, and was lowest in patients with larger tumours. 10 patients with hepatocellular carcinoma were treated with intratumoral injection of OK432. LAK activity was enhanced after treatment in 7 cases, and the percentage of Leu11b+ cells was increased. Enhancement of LAK activity in response to OK432 was more significant in patients with smaller rather than larger tumours. Of the 7 high LAK responders, 4 showed 50-100% tumour regression at 6-9 weeks after injection.

Extent of N-terminal methionine excision from Escherichia coli proteins is governed by the side-chain length of the penultimate amino acid

In a significant fraction of the Escherichia coli cytosolic proteins, the N-terminal methionine residue incorporated during the translation initiation step is excised. The N-terminal methionine excision is catalyzed by methionyl-aminopeptidase (MAP). Previous studies have suggested that the action of this enzyme could depend mainly on the nature of the second amino acid residue in the polypeptide chain. In this study, to achieve a systematic analysis of the specificity of MAP action, each of the 20 amino acids was introduced at the penultimate position of methionyl-tRNA synthetase of E. coli and the extent of in vivo methionine excision was measured. To facilitate variant protein purification and N-terminal sequence determination, an expression shuttle vector based on protein fusion with beta-galactosidase was used. From our results, methionine excision catalyzed by MAP is shown to obey the following rule: the catalytic efficiency of MAP, and therefore the extent of cleavage, decreases in parallel with the increasing of the maximal side-chain length of the amino acid in the penultimate position. This molecular model accounts for the rate of N-terminal methionine excision in E. coli, as deduced from the analysis of 100 protein N-terminal sequences.

Murine intracerebral interleukin-2 injection: pathological and immunological effects

The authors have investigated whether specific pathological changes and antibodies against interleukin-2 (IL-2) are induced after intracerebral administration of recombinant IL-2 (rIL-2). In addition, IL-2 receptor (IL-2R) expression was checked on the cell surface of normal brain tissues before and after the intracerebral infusion. Reconstituted rIL-2 (specific activity 1.2 x 10(7) U/mg protein) was injected into the right cerebral hemisphere of normal adult C57BL/6 mice in three different dose groups, each receiving single or multiple infusions of 8, 32, or 80 U. In sham control experiments, mouse albumin purified by gel filtration and ion exchange chromatography and adjusted to the same concentration of protein as rIL-2 was injected into mice at various doses. Anti-IL-2 antibodies were measured by an enzyme-linked immunosorbent assay concurrently with assessment of IL-2 activity in serum. The IL-2R expression was determined by using immunofluorescence techniques with monoclonal antibodies against mouse IL-2R. Since histological alteration after rIL-2 injection did not differ from that in the sham control preparations, it seems that there is no direct toxic action of rIL-2 on normal brain tissues. Interleukin-2 antibodies were produced at low levels only in mice injected repeatedly at the maximum dose, and levels were insignificant in other groups. Serum levels of IL-2 activity remained low. The IL-2R expression within the brain was not enhanced within 8 weeks following the intracerebral administration of rIL-2, suggesting that direct intracerebral infusion of rIL-2 may be safely used in the immunotherapy of brain tumors.

Characteristics of mouse lymphoid cells proliferating in vitro by recombinant human interleukin 2 (TGP-3): comparison between normal and nude mice

Various lymphoid cells obtained from BALB/c and BALB/c nu/nu mice were cultured in vitro with recombinant human interleukin 2 (rIL 2), and the characteristics of responder cells to rIL 2 were analyzed. Spleen cells, lymph node cells, and thymocytes except for bone marrow cells obtained from BALB/c mice remarkably proliferated in response to rIL 2. On the other hand, among lymphoid cells obtained from BALB/c nu/nu mice, only lymph node cells showed significant proliferation by rIL 2. Flow cytometric analysis revealed that mainly two types of lymphoid cells were proliferating in response to rIL 2 in BALB/c mice, i.e., Thy 1+, Lyt 1-, Lyt 2- and Thy 1+, Lyt 1-, Lyt 2+ cells. On the other hand, most of the proliferating cells were Thy 1+, Lyt 1-, Lyt 2- cells in BALB/c nu/nu mice. Treatment with various antibodies plus complement revealed that the majority of IL 2-responsive cells in BALB/c mice were Thy 1+, Lyt 1+, and Lyt 2+, although a minor part of them were Thy 1-, Lyt 1-, and Lyt 2-. On the other hand, a predominant type of the IL 2-responsive cells in BALB/c nu/nu mice were Thy 1-, Lyt 1-, and Lyt 2-, though some were Thy 1+. Nonspecific killer activity against tumor cells increased to variable extents in all of the lymphoid cells of both strains after culture with rIL 2. Our results indicate that mouse responder cells to rIL 2 have the following characteristics. First, the responder cells exist abundantly among spleen, lymph nodes, and thymus in normal mice, though their cell lineages are heterogeneous; one is of T cell lineage and the other of natural killer (NK) cell lineage. Second, nude mice are defective in the responder cells of T cell lineage but not of NK cell lineage. Moreover, the responder cells in nude mice predominantly accumulate in the lymph nodes but not other lymphoid organs.

Combination therapy of colon carcinoma 26 in mice with recombinant human interleukin-2 and interferon-alpha A/D: occurrence of large granular cells in the tumor

The antitumor effects of recombinant human interleukin-2 (rIL-2), in combination with recombinant human interferon-alpha A/D hybrid (rIFN-alpha A/D) on colon carcinoma 26 (colon 26) in mice were examined histologically. Colon 26 was transplanted subcutaneously into female BALB/c mice on day 0. The mice bearing the tumor received intramuscular injections of rIL-2, rIFN-alpha A/D or the combination of rIL-2 and rIFN-alpha A/D for 2-10 consecutive days starting on day 7. Mice were killed on days 9, 13, 17 and 21. After day 13, growth of the tumor was significantly suppressed in the mice treated with rIL-2 or rIFN-alpha A/D alone and was stopped in the mice treated with rIL-2 in combination with rIFN-alpha A/D. Histologically, tumor necrosis developed in all treated groups, though the degree was the most severe in the group receiving combination treatment. Many large cells (about 15-30 microns in diameter) infiltrated into the tumor, and they had Thy-1 surface antigen and many periodic acid-Schiff-positive round granules in the cytoplasm. The incidence of these large granular cells was correlated well with the reduction in tumor weight. The ultrastructural features of the large granular cells were very similar to those of murine large granular lymphocyte-like cells maintained in vitro in an IL-2-containing medium. The present large granular cells appear to be a kind of activated lymphoid cells.

Therapeutic efficacy of human recombinant interleukin-2 (TGP-3) alone or in combination with cyclophosphamide and immunocompetent cells in allogeneic, semi-syngeneic, and syngeneic murine tumors

The potential for a recombinant human interleukin-2 (rIL-2, TGP-3) alone, in combination with cyclophosphamide, and in combination with cyclophosphamide and normal immunocompetent cells to manifest biological activity in vivo was tested using allogeneic, semi-syngeneic, and syngeneic tumor-host systems in mice. The biological activity of rIL-2 was evaluated by the inhibition of the growth of tumors and the inhibition of metastases in short-term assays and, in long-term assays, the prolongation of the survival time of mice bearing subcutaneously (s.c.) or intradermally transplanted tumors. rIL-2 was injected s.c. daily continuously for up to 40 days or intermittently two to four times into mice bearing established tumors. In the short-term assays, the dose and schedule dependence of activity of rIL-2 alone was significantly manifested against sarcoma 180 in ICR mice (allogeneic) by the regression of the tumor, and was confirmed against Meth-A fibrosarcoma in BALB/c mice (syngeneic) by retarding the growth of the tumor. When assessed using these tumor, it was found that the antitumor activity of rIL-2 was schedule-dependent: the growth of tumors was more significantly suppressed when rIL-2 was injected every day for 10 days, starting on the 7th day after tumor transplantation, than when rIL-2 was injected five times every other day or twice every 5th day, even if the total amounts of rIL-2 injected were same. The continuous injection for 10 days was considered to be a standard regimen and the daily effective doses of rIL-2 were 5, 10, and 25 micrograms/mouse. Using the standard regimen and the effective doses, the activity of rIL-2 alone was also observed against two other syngeneic tumors: Colon carcinoma 26 in BALB/c mice, by retarding the growth of the tumor, and Lewis lung carcinoma in C57BL/6 mice by reducing the formation of lung metastases. When assessed using M5076 reticulum cell sarcoma, in a long-term assay, the activity of rIL-2 alone was not manifested in C57BL/6 mice (syngeneic) even when rIL-2 was injected for a long period (20 days) but it was observed in BDF1 (semi-syngeneic) mice. On the other hand, it was found that rIL-2 was effective in combination with cyclophosphamide in prolonging the survival time of C57BL/6 mice bearing the tumor.(ABSTRACT TRUNCATED AT 400 WORDS)

Lysis of human leukemic cells by monocyte-derived macrophages activated with interferon-gamma and interleukin-2

Cytolysis of leukemic cells by peripheral blood-derived macrophages was examined by means of an in vitro 111In release assay. Monocytes prepared on culture dishes lyse YK-M2. However, when monocytes were cultured in vitro and transformed into macrophages, they lost most of their lytic activity. The addition of human recombinant interleukin-2 (rIL-2) on day 5 in culture enhanced the lytic activity significantly. Similarly, treatment of macrophages with human recombinant interferon gamma (rIFN-gamma) promoted the lysis of YK-M2 and K-562, although the extent of lysis was smaller than that by rIL-2. Macrophages activated with rIL-2 and rIFN-gamma also lysed human leukemic cells. Activated macrophages lysed leukemic cells of acute myelocytic leukemia more than acute lymphocytic leukemia cells. Macrophages derived from the peripheral blood of patients with leukemia were examined for their lytic activity against YK-M2. The patient's macrophages lysed more YK-M2 than did control macrophages when they were activated with rIL-2 and rIFN-gamma. The macrophages of two patients also demonstrated autologous leukemic cell lysis.

The analysis of recombinant interleukin-2 by thermospray liquid chromatography-mass spectrometry

The complete sequence of recombinant human interleukin-2 expressed in Escherichia coli has been confirmed by thermospray liquid chromatography-mass spectrometry (TS-LC-MS) of a tryptic digest derived from 100 micrograms (7 nmol) of reduced carboxymethylated interleukin-2. The preparation was shown by this method to contain predominantly unprocessed N-terminal initiator Met, with some authentic N-terminal Ala; the rest of the protein was as predicted from the DNA sequence, though some deamidated material was noted. TS-LC-MS proved to be a rapid and efficient method for surveying the protein tryptic peptide products allowing all the data to be collected in one chromatographic run; all tryptic fragments were identified by their molecular ions including those for the larger peptides (Mr 1500-3500) which, due to the presence of doubly and triply charged molecular ions, were brought within the mass range of the instrument (1800 Da). It is proposed that TS-LC-MS is a good general method for analyzing recombinant protein digests with respect to sequence confirmation, processing, and post-translational modification, and since each chromatographic peak is identified allows for subsequent monitoring of the protein by LC using uv detection. The method suffers from the disadvantages that all the sample is consumed during the experiment and that no fragment (sequence) ions are generally observed.

Effect of recombinant human interleukin-2 on the course of experimental chronic respiratory tract infection caused by Klebsiella pneumoniae in mice

The effect of recombinant human interleukin-2 (rIL-2) on the course of experimental chronic respiratory tract infection caused by Klebsiella pneumoniae in mice was examined. rIL-2 was administered subcutaneously once a day for 7 or 14 days, starting 2 weeks after the mice were infected. Administration of 2 or 20 micrograms of rIL-2 per mouse daily for 7 days reduced bacterial counts in the lungs dose dependently. At a dose of 0.2 microgram per day, proliferation of bacteria in the lungs was suppressed after 14 days of administration. Agglutinin titers in serum were not affected by rIL-2 treatment. Monocyte and lymphocyte counts in peripheral blood were increased by administration of 20 micrograms of rIL-2 daily for 14 days but not by treatment for 7 days. In addition, clearance of bacteria from the lungs after aerosol exposure was enhanced by treatment for 7 days before infection. Thus, rIL-2 acted therapeutically or prophylactically in the presence or absence, respectively, of a specific antigen. These effects were not abolished by anti-asialo GM1 antibody. This suggests that activation of natural killer cells does not play a critical role in the therapeutic and prophylactic effects of rIL-2.

Characterization of human and mouse granulocyte-macrophage-colony-stimulating factors derived from Escherichia coli

Human and mouse granulocyte-macrophage-colony-stimulating factors (hGM-CSF and mGM-CSF, respectively), isolated from Escherichia coli cells expressing the corresponding human and mouse genes, have been characterized. The observed properties of the proteins have been compared with those properties which can be deduced from the DNA sequence alone and the published properties of natural GM-CSFs. The purified E. coli-derived proteins were found to have the expected molecular masses, amino acid compositions and N- and C-terminal amino acid sequences. The finding of 70-90% unprocessed N-terminal methionine for both proteins is discussed. The four Cys residues were found to be involved in two intramolecular disulphide bonds, linking the first and third, and second and fourth Cys residues. This disulphide bond arrangement is probably the one existing in natural material, since, although not glycosylated, both E. coli-derived proteins showed biological activity (colony stimulating assay for hGM-CSF, and cell proliferation assay for mGM-CSF) comparable with that reported for the respective proteins purified from animal cells.

Crystallographic characterization of recombinant human interleukin 2

Recombinant human interleukin 2 produced by Escherichia coli was purified to homogeneity and crystallized after being separated from methionyl interleukin 2. Crystals suitable for structural studies have been obtained by the seed enlargement technique, using the method of vapor diffusion with ammonium sulfate as the precipitant at pH 4.6. The space group is P2(1)2(1)2 with cell dimensions a = 49.2 A, b = 87.6 A and c = 32.4 A. The asymmetric unit contains one molecule of the protein. From preliminary results, the crystals are moderately stable to X-rays and produce measurable reflections to a resolution of about 2.2 A. The diffraction data for the native crystals have been collected on a diffractometer at 2.4 A resolution.

Importance of disulfide linkage for constructing the biologically active human interleukin-2

Recombinant human interleukin-2 (rIL-2) produced in Escherichia coli possesses a free thiol group at Cys-125 and a disulfide linkage between Cys-58 and Cys-105, as in the case for natural human interleukin-2. Treatment of rIL-2 with 200 mM dithiothreitol resulted in the cleavage of the Cys-58-Cys-105 disulfide bond. The reduced form of rIL-2 thus obtained retained only 10% of the in vitro biological activity of the native form, as measured by the ability to stimulate the growth of an IL-2-dependent mouse natural killer cell line, NKC3. Far-uv circular dichroism studies indicated that the cleavage of the disulfide bond results in a decrease of alpha-helix content. Near-uv circular dichroism studies suggested that the native molecule is folded into a rigid tertiary structure, while the reduced form showed a spectrum similar to that of rIL-2 denatured in the presence of 6 M guanidine.HCl. The once-reduced molecule was readily reoxidized in the presence of 10 microM Cu2+ to form the native molecule with full biological activity. These results strongly demonstrate that the Cys-58-Cys-105 disulfide linkage in the IL-2 molecule is essential for constructing a rigid and biologically active form of IL-2.

The state of the N-terminus of recombinant proteins: determination of N-terminal methionine (formylated, acetylated, or free)

The removal of N-terminal methionine from proteins produced by recombinant DNA techniques is often far from quantitative. Furthermore, a proportion of the methionylated product may be N alpha-blocked and thus not easily accessible to conventional (Edman) techniques of protein characterization. In this paper, a method for overcoming the resulting analytical problems is described. The technique is based on perdeuteroacetylation (performed only if unblocked methionine is to be determined), cleavage with cyanogen bromide, extraction of any acylhomoserine lactone into ethyl acetate, formation of a chemical derivative, and analysis by combined gas-liquid chromatography/mass spectrometry (GC/MS). The remaining cyanogen bromide fragments, insoluble in ethyl acetate, are available for further analysis by mass spectrometric or other methods if required. Using an acylhomoserine lactone labeled with a stable isotope as internal standard, the method is semiquantitative. It should be possible to develop a quantitative method if appropriate polypeptide standards are prepared. N-Terminal processing of eight recombinant-derived proteins is discussed.

Purification and renaturation of recombinant human interleukin-2

Recombinant human interleukin-2 (IL-2) expressed as Escherichia coli was isolated as insoluble aggregates of protein (inclusion bodies) after cell breakage. IL-2 and contaminants were dissolved in 6 M-guanidinium chloride/10 mM-dithiothreitol, pH 8.5, and further purified in reduced and denatured form by gel-permeation chromatography in the same solvent. Renaturation was effected by dilution and autoxidation; IL-2 of native specific activity was isolated at over 95% purity by reversed-phase h.p.l.c.; an additional peak of reduced protein was also observed. Most losses of native IL-2 occurred on refolding, probably because of an aggregation process; concentrations around 1 microgram/ml were necessary to achieve 30% recovery. It was essential to maintain the denatured protein in reduced form before renaturation and autoxidation, which was most efficient at pH 8.5 with 1.5 microM-CuSO4. A procedure based on these observations has been used to prepare IL-2 on the 50 micrograms scale.

Micropreparative purification of recombinant human interleukin-2

Recombinant Interleukin-2 (IL-2) is expressed in E. coli as insoluble aggregates; a protocol has been developed for solubilization, renaturation and purification of IL-2 from such aggregates at the 5-10-mg level. IL-2 aggregates were isolated from soluble proteins by centrifugation, subjected to a 1 M guanidine hydrochloride wash and a butan-1-ol wash (the latter to remove lipid), dissolved in 8 M guanidine hydrochloride-10 mM dithiothreitol and partly purified by gel permeation chromatography. Refolding/oxidation was then performed by dilution into Tris-HCl, pH 8.5 containing 1.5 microM copper sulphate to accelerate autoxidation. Final purification was by successive cation-exchange and reversed-phase high-performance liquid chromatographic steps, yielding over 99.5% pure IL-2 with an overall recovery of 20%.

N-terminal-methionylated interleukin-1 beta has reduced receptor-binding affinity

The receptor-binding affinity of recombinant-derived interleukin-1 beta containing unprocessed N-terminal methionine (MAPV-) was 10-fold lower than protein containing the authentic N-terminal sequence (APV-). Structural analysis of the methionylated and non-methionylated proteins by NMR spectroscopy detected no (or minor) conformational differences. The differences in binding affinity, therefore, suggest that the additional N-terminal methionine causes a small, direct or indirect, perturbation of the receptor-binding region.

An enzyme-immunoassay for human interleukin-2

A highly sensitive enzyme-immunoassay (EIA) for human interleukin-2 (IL-2) has been established. The assay is based on a sandwich method that uses two kinds of anti-IL-2 antibodies raised against Escherichia coli-derived recombinant IL-2 (rIL-2). An affinity-purified-anti-IL-2 goat IgG was used as the first antibody and the Fab' fragment of an affinity-purified-anti-IL-2 rabbit IgG was used as the second antibody after being coupled with horseradish peroxidase (HRP). As little as 30 pg/ml of IL-2 was detected by the EIA, indicating that this method was about 100 times more sensitive than the bioassay using an IL-2-dependent murine natural killer cell line, NKC3. There was a good correlation between the EIA and the bioassay (r = 0.998).

Chromatofocusing of N-terminally processed forms of proteins. Isolation and characterization of two forms of interleukin-1 beta and of bovine growth hormone

Using chromatofocusing, two fractions have been obtained from recombinant-derived interleukin-1 beta (IL-1 beta) and from pituitary-derived bovine growth hormone (BGH). The forms of both proteins responsible for these fractions have been characterized by N-terminal and C-terminal amino acid sequence determination. Recombinant IL-1 beta, as a mixture of correctly processed polypeptide and an N-terminally methionylated form, was resolved rapidly by chromatofocusing. BGH was resolved into the full-length polypeptide commencing Ala-Phe-Pro-Ala-Met-Ser-Leu- and a form truncated at the N-terminus by four amino acid residues, which thus commences Met-Ser-Leu-; the fraction containing the truncated form also contains a species having N-terminal Phe-Pro-Ala-. These results, and the possible generality of the separation, are discussed.

Structure-activity studies of interleukin-2

The critical role of interleukin-2 (IL-2) in immune response heightens the need to know its structure in order to understand its activity. New computer-assisted predictive methods for the assignment of secondary structure together with a method to predict the tertiary structure of a protein from data on its primary sequence and secondary structure were applied to IL-2. This method generated four topological families of structures, of which the most plausible is a right-handed fourfold alpha-helical bundle. Members of this family were shown to be compatible with existing structural data on disulfide bridges and monoclonal antibody binding for IL-2. Experimental estimates of secondary structure from circular dichroism and site-directed mutagenesis data support the model. A region likely to be important in IL-2 binding to its receptor was identified as residues Leu36, Met38, Leu40, Phe42, Phe44, and Met46.