High-level expression and purification of recombinant huGM-CSF (9-127)/IL-6 (29-184) fusion protein in Escherichia coil

As HuGM-CSF and huIL-6 seem to have synergistic and complementary actions, researchers have proposed that fusion proteins incorporating these two cytokines could show increased biological activity, especially in terms of hematopoietic function. Here, we sought to obtain a functional GM-CSF/IL-6 fusion protein and to investigate its biological activities in vitro. A novel construct encoding a fusion protein of huGM-CSF (9-127) and IL-6 (29-184) was generated in the pBV220 expression vector by step-by-step cloning. Amino acids 1-8 of huGM-CSF and amino acids 1-28 of huIL-6 were deleted by PCR. The mutant huGM-CSF (9-127) and huIL-6 (29-184) cDNAs were linked via a linker sequence encoding 15 amino acid residues (G-G-S-G-S)3. Direct sequencing was used to confirm the validity of the desired construct, and the fusion protein was expressed in Escherichia coli host strain BL21 (DE3) in the form of inclusion bodies (IBs). The expression level was more than 25% of the total cell lysate, and a novel purification and refolding strategy was used to isolate the fusion protein product. Inclusion bodies were purified by Q Sepharose H.P. ion exchange in 8 mol/L urea, followed by in situ refolding by Sephacryl S-200. The renatured fusion proteins were obtained at a purity of >95%, and the strategy of refolding on the gel filtration column was found to be efficient, with a relative refolding rate of 80%. This entire refolding and purification procedure could be performed within one day and may prove applicable to large-scale purification and refolding of recombinant proteins from IBs in E. coli. This new method was used to obtain huGM-CSF (9-127)/IL-6 (29-184) fusion protein with high purity and biological activity. MTT assays in TF-1 and B9 cell lines showed that the specific biological activity of huGM-CSF was 1.14+/-0.10 x 10(8) U/mg, and that for huIL-6 was 1.89+/-0.11 x 10(7) U/mg. The fusion protein exhibited enhanced huGM-CSF, but similar huIL-6 biological activities compared with those of either GM-CSF or IL-6 alone. This suggests that our novel huGM-CSF (9-127)/IL-6 (29-184) fusion protein may hold future promise as a therapeutic agent.     

Determination of the functional epitopes of human interleukin-18-binding protein by site-directed mutagenesis

The human interleukin (IL)-18-binding protein (hIL-18BP) is a naturally occurring antagonist of IL-18, a proinflammatory cytokine that is related to IL-1beta and has an important role in defense against microbial invaders. As its name implies, the hIL-18BP binds to IL-18 with high affinity and prevents the interaction of IL-18 with its receptor. We genetically modified the C terminus of hIL-18BP by appending a 15-amino acid biotinylation recognition site and a six-histidine tag and then performed site-directed mutagenesis to determine the functional epitopes that mediate efficient binding to IL-18. The mutated IL-18BPs were secreted from mammalian cells, captured by metal affinity chromatography, biotinylated in situ, eluted, and immobilized on streptavidin-coated chips. Using surface plasmon resonance, we identified seven amino acids of hIL-18BP which, when changed individually to alanine, caused an 8-750-fold decrease in binding affinity, largely because of increased off-rates. These seven amino acids localized to the predicted beta-strand c and d of hIL-18BP immunoglobulin-like domain, and most had hydrophobic side chains. Just two amino acids, tyrosine 97 and phenylalanine 104, contributed approximately 50% of the binding free energy. Information obtained from these studies could contribute to the design of molecular antagonists of IL-18 for treatment of inflammatory diseases.     

The N-terminal domain of tissue inhibitor of metalloproteinases retains metalloproteinase inhibitory activity

Recombinant tissue inhibitor of metalloproteinases (TIMP-1) and a truncated version containing only the three N-terminal loops, delta 127-184TIMP, have been expressed in myeloma cells and purified by affinity chromatography and gel filtration. delta 127-184TIMP was found to exist as two main glycosylation variants of molecular mass 24 kD and 19.5 kDa and an unglycosylated form of 13 kDa. All forms of the truncated inhibitor were able to inhibit and form complexes with active forms of the matrix metalloproteinases, indicating that the major structural features for specific interaction with these enzymes resides in these three loops. Stable binding of delta 127-184TIMP to pro 95-kDa gelatinase was not demonstrable under the conditions for binding of full-length TIMP-1.     

Structure-function analysis of human IL-6: identification of two distinct regions that are important for receptor binding.

Interleukin-6 (IL-6) is a multifunctional cytokine that plays an important role in host defense. It has been predicted that IL-6 may fold as a 4 alpha-helix bundle structure with up-up-down-down topology. Despite a high degree of sequence similarity (42%) the human and mouse IL-6 polypeptides display distinct species-specific activities. Although human IL-6 (hIL-6) is active in both human and mouse cell assays, mouse IL-6 (mIL-6) is not active on human cells. Previously, we demonstrated that the 5 C-terminal residues of mIL-6 are important for activity, conformation, and stability (Ward LD et al., 1993, Protein Sci 2:1472-1481). To further probe the structure-function relationship of this cytokine, we have constructed several human/mouse IL-6 hybrid molecules. Restriction endonuclease sites were introduced and used to ligate the human and mouse sequences at junction points situated at Leu-62 (Lys-65 in mIL-6) in the putative connecting loop AB between helices A and B, at Arg-113 (Val-117 in mIL-6) at the N-terminal end of helix C, at Lys-150 (Asp-152 in mIL-6) in the connecting loop CD between helices C and D, and at Leu-178 (Thr-180 in mIL-6) in helix D. Hybrid molecules consisting of various combinations of these fragments were constructed, expressed, and purified to homogeneity. The conformational integrity of the IL-6 hybrids was assessed by far-UV CD. Analysis of their biological activity in a human bioassay (using the HepG2 cell line), a mouse bioassay (using the 7TD1 cell line), and receptor binding properties indicates that at least 2 regions of hIL-6, residues 178-184 in helix D and residues 63-113 in the region incorporating part of the putative connecting loop AB through to the beginning of helix C, are critical for efficient binding to the human IL-6 receptor. For human IL-6, it would appear that interactions between residues Ala-180, Leu-181, and Met-184 and residues in the N-terminal region may be critical for maintaining the structure of the molecule; replacement of these residues with the corresponding 3 residues in mouse IL-6 correlated with a significant loss of alpha-helical content and a 200-fold reduction in activity in the mouse bioassay. A homology model of mIL-6 based on the X-ray structure of human granulocyte colony-stimulating factor is presented.     

Identification of amino acid residues of gp130 signal transducer and gp80 alpha receptor subunit that are involved in ligand binding and signaling by human herpesvirus 8-encoded interleukin-6

Human herpesvirus 8-encoded interleukin-6 (vIL-6) signals through the gp130 signal transducer but is not dependent on the IL-6 receptor alpha subunit (IL-6R, gp80) that is required for signaling by endogenous IL-6 proteins; however, IL-6R can enhance vIL-6 activity and can enable signaling through a gp130 variant, gp130.PM5, that is itself unable to support vIL-6 signaling. These findings suggest that the vIL-6-gp130 interactions are qualitatively different from those of human IL-6 (hIL-6) and that vIL-6 signaling may be more promiscuous than that of hIL-6 but that IL-6R may play a role in vIL-6 signaling in vivo. To examine the receptor binding requirements of vIL-6, we have undertaken mutational analyses of regions of gp130 and IL-6R potentially involved in interactions with ligand or in functional complex formation and used these variants in functional, ligand-binding, and receptor dimerization assays. The data presented identify positions within two interstrand loops of the gp130 cytokine-receptor homology domain that are important for vIL-6 signaling and vIL-6-induced receptor dimerization and show that vIL-6, like hIL-6, can form complexes with IL-6R and gp130 but that the roles of putative cytokine-binding residues of IL-6R in ligand-induced functional complex formation are qualitatively different in the case of vIL-6 and hIL-6.     

Engineering human interleukin-6 to obtain variants with strongly enhanced bioactivity.

Interleukin-6 (IL-6) triggers the formation of a high affinity receptor complex with the ligand binding subunit IL-6Ralpha and the signal transducing chain gp130. Since the intracytoplasmic region of the IL-6Ralpha does not contribute to signaling, soluble forms of the extracytoplasmic domain (sIL-6Ralpha), potentiate IL-6 bioactivity and induce a cytokine-responsive status in cells expressing gp130 only. This observation, together with the detection of high levels of circulating soluble human IL-6Ralpha (shIL-6Ralpha) in sera, suggests that the hIL-6-shIL-6Ralpha complex is an alternative form of the cytokine. Here we describe the generation of human IL-6 (hIL-6) variants with strongly enhanced shIL-6Ralpha binding activity and bioactivity. Homology modeling and site-directed mutagenesis of hIL-6 suggested that the binding interface for hIL-6Ralpha is constituted by the C-terminal portion of the D-helix and residues contained in the AB loop. Four libraries of hIL-6 mutants were generated by each time fully randomizing four different amino acids in the predicted AB loop. These libraries were displayed monovalently on filamentous phage surface and sorted separately for binding to immobilized shIL-6Ralpha. Mutants were selected which, when expressed as soluble proteins, showed a 10- to 40-fold improvement in shIL-6Ralpha binding; a further increase (up to 70-fold) was achieved by combining variants isolated from different libraries. Interestingly, high affinity hIL-6 variants show strongly enhanced bioactivity on cells expressing gp13O in the presence of shIL-6Ralpha at concentrations similar to those normally found in human sera.     

The existence of multiple conformers of interleukin-21 directs engineering of a superpotent analogue

The high resolution three-dimensional structure of human interleukin (hIL)-21 has been resolved by heteronuclear NMR spectroscopy. Overall, the hIL-21 structure is dominated by a well defined central four-helical bundle, arranged in an up-up-down-down topology, as observed for other cytokines. A segment of the hIL-21 molecule that includes the third helical segment, helix C, is observed to exist in two distinct and interchangeable states. In one conformer, the helix C segment is presented in a regular, alpha-helical conformation, whereas in the other conformer, this segment is largely disordered. A structure-based sequence alignment of hIL-21 with receptor complexes of the related cytokines, interleukin-2 and -4, implied that this particular segment is involved in receptor binding. An hIL-21 analog was designed to stabilize the region around helix C through the introduction of a segment grafted from hIL-4. This novel hIL-21 analog was demonstrated to exhibit a 10-fold increase in potency in a cellular assay.     

Production of recombinant hIL-4delta2-a native isoform of human interleukin-4 in Escherichia coli cells

Expression plasmids containing the synthetic gene hil-4 delta 2 was constructed to produce human interleukin-4 in Escherichia coli cells. Strains TG1 (pBTIL-4 delta 2) and BL21 (DE3) (pETIL-4 delta 2) produced the recombinant protein as inclusion bodies, and its production level was up to 30% of the total cell protein. The renatured hIL-4 delta 2 inhibited IL-4-stimulated T cell proliferation, and this effect was enhanced by cyclosporin A.     

人IL-6 /sIL-6R 结合分子模型的建立及在药物筛选中的应用

目的：建立人IL-6 /sIL-6R 结合的分子模型,用于筛选IL-6 /sIL-6R的抑制剂。方法：将人IL-6基因克隆至原核表达载体pET28a（+）中表达IL-6蛋白,western blot及人IL-6检测试剂盒分析鉴定表达蛋白。同法将人sIL-6R在pET15b载体中表达,纯化并用western blot检测目的蛋白。依据ELISA原理建立IL-6 /sIL-6R 结合的分子模型,并通过改变IL-6、sIL-6R及IL-6 antibody的浓度来优化该模型,用于IL-6 /sIL-6R拮抗药物的筛选。结果：人IL-6可在载体PET28a（+）中高效表达,且经western blot鉴定正确,人IL-6检测试剂盒检测显示具有较高的免疫活性。sIL-6R在PET15b中表达,western blot鉴定正确。通过对IL-6 /sIL-6R结合的分子模型的优化,得到其最佳条件为：IL-6R 1?g/well, IL-6 500ng/well, IL-6 antibody 1?g/well。应用该模型筛选发现有些化合物可显著抑制IL-6与其受体的结合。结论：成功构建IL-6 /sIL-6R结合的分子模型,为高通量筛选IL-6拮抗剂提供平台。     

Expression of murine IL-2 receptor beta-chain on thymic and splenic lymphocyte subpopulations as revealed by the IL-2-induced proliferative response in human IL-2 receptor alpha-chain transgenic mice

Lymphocytes from the human (h) IL-2R alpha chain transgenic mice (TGM) constitutively express high affinity binding sites for hIL-2, consisting of transgenic h-IL-2R alpha and endogenous murine IL-2R beta, and therefore easily proliferate in vitro in response to hIL-2. Our study was undertaken to clarify the hIL-2-responsive lymphocyte subsets in the TGM, which should most likely reflect the normal distribution of m IL-2R beta expression. In both thymus and spleen, the majority of expanded cells by hIL-2 was CD3+CD4-CD8+ TCR alpha beta+ cells. The proliferation of CD4+ cells was not observed at all from either organ despite the expression of transgenic hIL-2R alpha. Potent cellular proliferation was also observed from the thymocytes that had been depleted of CD8+ cells, the expanded cells consisting of CD3- (15-40%) and CD3+ populations (60-85%). Among CD3+ cells, approximately the half portion expressed TCR alpha beta, whereas the other half was suggested to express TCR gamma delta. A variable portion (5-20%) of the CD3+ cells expressed CD8 (Lyt-2) in the absence of Lyt-3, and the CD3+CD8+ cells were confined preferentially to the TCR alpha beta- (TCR gamma delta+) population. In the culture of splenocytes depleted of CD8+ cells, however, the proliferated cells were mostly CD3-CD4-CD8-TCR-Mac1-, whereas a minor portion (10-30%) was CD3+CD4-CD8-TCR alpha beta- (TCR gamma delta+. Analysis of TCR genes at both DNA and mRNA levels confirmed the phenotypical observations. These results strongly suggested that IL-2R beta was constitutively and selectively expressed on the primary murine thymocytes and splenic T and NK cells, except for CD4+ cells in both organs.     

Structural requirements for gp80 independence of human herpesvirus 8 interleukin-6 (vIL-6) and evidence for gp80 stabilization of gp130 signaling complexes induced by vIL-6

Human herpesvirus 8 interleukin-6 (vIL-6) displays 25% amino acid identity with human IL-6 (hIL-6) and shares an overall four-helix-bundle structure and gp130-mediated STAT/mitogen-activated protein kinase signaling with its cellular counterpart. However, vIL-6 is distinct in that it can signal through gp130 alone, in the absence of the nonsignaling gp80 alpha-subunit of the IL-6 receptor. To investigate the structural requirements for gp80 independence of vIL-6, a series of expression vectors encoding vIL-6/hIL-6 chimeric and site-mutated IL-6 proteins was generated. The replacement of hIL-6 residues with three vIL-6-specific tryptophans implicated in gp80 independence from crystallographic studies or the A and C helices containing these residues did not confer gp80 independence to hIL-6. The N- and C-terminal regions of vIL-6 could be substituted with hIL-6 sequences with the retention of gp80-independent signaling, but substitutions of other regions of vIL-6 (helix A, A/B loop, helix B, helix C, and proximal half of helix D) with equivalent sequences of hIL-6 abolished gp80 independence. Interestingly, the B helix of vIL-6 was absolutely required for gp80 independence, despite the fact that this region contains no receptor-binding residues. Point mutational analysis of helix C, which contains residues involved in physical and functional interactions with gp130 domains 2 and 3 (cytokine-binding homology region), identified a variant, VI120EE, that was able to signal and dimerize gp130 only in the presence of gp80. gp80 was also found to stabilize gp130:g130 dimers induced by a distal D helix variant of vIL-6 that was nonetheless able to signal independently of gp80. Together, our data reveal the crucial importance of overall vIL-6 structure and conformation for gp80-independent signaling and provide functional and physical evidence of the stabilization of vIL-6-induced gp130 signaling complexes by gp80.     

Receptors for interleukin-13 and interleukin-4 are complex and share a novel component that functions in signal transduction.

Interleukin-4 (IL-4) and interleukin-13 (IL-13) are two cytokines that are secreted by activated T cells and have similar effects on monocytes and B cells. We describe a mutant form of human interleukin-4 (hIL-4) that competitively antagonizes both hIL-4 and human interleukin-13 (hIL-13). The amino acid sequences of IL-4 and IL-13 are approximately 30% homologous and circular dichroism (CD) spectroscopy shows that both proteins have a highly alpha-helical structure. IL-13 competitively inhibited binding of hIL-4 to functional human IL-4 receptors (called hIL-4R) expressed on a cell line which responds to both hIL-4 and IL-13. Binding of hIL-4 to an hIL-4 responsive cell line that does not respond to IL-13, and binding of hIL-4 to cloned IL-4R ligand binding protein expressed on heterologous cells, were not inhibited by IL-13. hIL-4 bound with approximately 100-fold lower affinity to the IL-4R ligand binding protein than to functional IL-4R. The mutant hIL-4 antagonist protein bound to both IL-4R types with the lower affinity. The above results demonstrate that IL-4 and IL-13 share a receptor component that is important for signal transduction. In addition, our data establish that IL-4R is a complex of at least two components one of which is a novel affinity converting subunit that is critical for cellular signal transduction.     

Three-dimensional structure and function study on the active region in the extracellular ligand-binding domain of human IL-6 receptor

In this study the three-dimensional (3-D) model of the ligand-binding domain (V106-P322) of human interleukin-6 receptor (hIL-6 R) was constructed by computer-guided homology modeling technique using the crystal structure of the ligand-binding domain (K52-L251) of human growth hormone receptor (hGHR) as templet. Furthermore, the active binding region of the 3-D model of hIL-6R with the ligand (hIL-6) was predicted. In light of the structural characteristics of the active region, a hydrophobic pocket shielded by two hydrophilic residues (E115 and E505) of the region was identified by a combination of molecular modelling and the site-directed or double-site mutation of the twelve crucial residues in the ligand-binding domain of hIL-6R (V106-P322). We observed and analyzed the effects of these mutants on the spatial conformation of the pocket-like region of hIL-6 R. The results indicated that any site-directed mutation of the five Cys residues (four conservative Cys residues: Cys121, Cys132, Cys165, Cys176; near membrane Cys residue: Cys193) or each double-site mutation of the five residues in WSEWS motif of hIL-6R (V106-P322) makes the corresponding spatial conformation of the pocket region block the linkage between hIL-6 R and hIL-6. However, the influence of the site-directed mutation of Cys211 and Cys277 individually on the conformation of the pocket region benefits the interaction between hIL-6R and hIL-6. Our study suggests that the predicted hydrophobic pocket in the 3-D model of hIL-6R (V106-P322) is the critical molecular basis for the binding of hIL-6R with its ligand, and the active pocket may be used as a target for designing small hIL-6R-inhibiting molecules in our further study.     

Correspondence of the functional epitopes of poxvirus and human interleukin-18-binding proteins

Molluscum contagiosum virus, a human poxvirus that causes persistent small benign skin tumors, encodes a variety of putative immune defense proteins. Three such proteins, MC51L, MC53L, and MC54L, have 20 to 35% amino acid sequence identities with human interleukin-18 (hIL-18)-binding protein (hIL-18BP), a naturally occurring antagonist of the proinflammatory cytokine IL-18. We previously demonstrated that seven amino acids within the immunoglobulin-like domain of hIL-18BP were important for high-affinity binding to hIL-18. Model building indicated that MC54L, which has been shown to bind hIL-18, contains five of the seven amino acids at corresponding positions in its immunoglobulin-like domain, the exceptions being the conservative substitution of isoleucine for a leucine and the nonconservative substitution of valine for a phenylalanine. We found that individual alanine substitutions for these six identical or highly conserved amino acids of MC54L caused changes in affinity and binding free energy for hIL-18 that were quantitatively similar to those produced by mutagenesis of hIL-18BP. Furthermore, when the nonconserved valine of MC54L was mutated to phenylalanine, making it more like hIL-18BP, its affinity for hIL-18 increased more than 10-fold. In addition, the carboxyl-terminal half of MC54L, which has no similarity with hIL-18BP, was dispensable for hIL-18 binding. Thus, despite their relatively low overall sequence identity, MC54L and hIL-18BP have similar hIL-18 binding sites and functional epitopes. On the other hand, MC51L and MC53L have nonconservative substitutions of three to six of the seven critical amino acids of hIL-18BP and neither protein bound hIL-18, suggesting that they may interact with unidentified ligands.     

IL-6, leukemia inhibitory factor,and oncostatin M stimulate bone resorption and regulate the expression of receptor activator of NF-kappa B ligand,osteoprotegerin, and receptor activator of NF-kappa B in mouse calvariae

IL-6, leukemia inhibitory factor (LIF), and oncostatin M (OSM) are IL-6-type cytokines that stimulate osteoclast formation and function. In the present study, the resorptive effects of these agents and their regulation of receptor activator of NF-kappaB ligand (RANKL), RANK, and osteoprotegerin (OPG) were studied in neonatal mouse calvaria. When tested separately, neither human (h) IL-6 nor the human soluble IL-6R (shIL-6R) stimulated bone resorption, but when hIL-6 and the shIL-6R were combined, significant stimulation of both mineral and matrix release from bone explants was noted. Semiquantitative RT-PCR showed that hIL-6 plus shIL-6R enhanced the expression of RANKL and OPG in calvarial bones, but decreased RANK expression. Human LIF, hOSM, and mouse OSM (mOSM) also stimulated 45Ca release and enhanced the mRNA expression of RANKL and OPG in mouse calvaria, but had no effect on the expression of RANK. In agreement with the RT-PCR analyses, ELISA measurements showed that both hIL-6 plus shIL-6R and mOSM increased RANKL and OPG proteins. 1,25-Dihydroxyvitamin D3 (D3) also increased the RANKL protein level, but decreased the protein level of OPG. OPG inhibited 45Ca release stimulated by RANKL, hIL-6 plus shIL-6R, hLIF, hOSM, mOSM, and D3. An Ab neutralizing mouse gp130 inhibited 45Ca release induced by hIL-6 plus shIL-6R. These experiments demonstrated stimulation of calvarial bone resorption and regulation of mRNA and protein expression of RANKL and OPG by D3 and IL-6 family cytokines as well as regulation of RANK expression in preosteoclasts/osteoclasts of mouse calvaria by D3 and hIL-6 plus shIL-6R.     

JAK1 N-terminus binds to conserved Box 1 and Box 2 motifs of cytokine receptor common beta subunit but signal activation requires JAK1 C-terminus

The human interleukin-3 receptor (hIL-3R) consists of a unique alpha subunit (hIL-3Ralpha) and a common beta subunit (betac). Binding of IL-3 to IL-3R activates Janus kinases JAK1 and JAK2. Our previously study showed that JAK2 and JAK1 were constitutively associated with the hIL-3Ralpha and betac subunits, respectively. In this study, we further demonstrate that JAK2 binds to the intracellular domain of hIL-3Ralpha and JAK1 binds to the Box 1 and Box 2 motifs of betac using GST-hIL-3R fusion proteins in pull-down assays. JAK1 mutational analysis revealed that its JH7-3 domains bound directly to the Box 1 and Box 2 motifs of betac. We further examined the role of JAK1 JH7-3 domains in JAK1 and JAK2-mediated signaling using the CDJAKs fusion proteins, which consisted of a CD16 extracellular domain, a CD7 transmembrane domain, and either JAK1 (CDJAK1), JAK2 (CDJAK2), or JAK1-JH7-3 domains (CDJAK1-JH7-3) as intracellular domains. Anti-CD16 antibody crosslinking of wild type fusion proteins CDJAK1 with CDJAK2 could mimic IL-3 signaling, however, the crosslinking of fusion proteins CDJAK1-JH7-3 with CDJAK2 failed to activate downstream proteins. These results suggest that the JAK1-JH7-3 domains are required for betac interaction and abolish wild type JAK1 and JAK2-mediated signaling.     

Enhanced protease cleavage efficiency on the glucagon-fused interleukin-2 by the addition of synthetic oligopeptides

Human interleukin-2 (hIL-2) was produced as a recombinant fusion protein (G3.IL-2/HF) consisting of three tandem-arranged human glucagon molecules (G3) and hIL-2. For the recovery of hIL-2, a factor Xa (FXa) cleavage sequence was introduced next to the N-terminus of hIL-2. Cleavage efficiency on this recombinant protein construct was very low because its recognition sequence was sterically hindered within the G3.IL-2/HF molecule and hence FXa access to the cleavage site was insufficient. We therefore introduced various synthetic oligopeptides upstream from the FXa cleavage site as a means to change substrate conformation and thereby increase cleavage efficiency. Among these oligopeptides, acidic or nucleophilic constructs were the most effective for the FXa-mediated cleavage of the fusion protein. In addition, insertion of various oligopeptides into the G3.IL-2/HF molecule varied the solubility of each construct depending on their physical properties. Consequently, the G3.IL-2/DF construct showed the highest final hIL-2 yields via FXa-mediated removal of the fusion partner. Lastly, we confirmed that cleavage efficiency was greatly increased but native hIL-2 was cleaved internally by non-specific cleavage when the acidic oligopeptide D4 (DDDD) was introduced upstream of the EK cleavage site within G3.IL-2/HE molecule. The G3.IL-2/HE molecule was shown to be an inefficient substrate to EK in a previous report (Biotechnol. Bioprocess Eng. (2000) 5, 13-16).