Three-dimensional model of a human interferon-alpha consensus sequence

Evaluation of a single amino acid substitution at position 79 of human IFN-α2b in interferon-receptor assembly and activity

Type I interferons (IFNs) are homologous cytokines that bind to a cell surface receptor and establish signaling pathways that motivate immune responses. The purpose of the current study is to assess the activity of a novel-engineered IFN-α2b. The crystallographic structure of IFN-α2b and its receptors was acquired from Protein Data Bank. Various amino acid substitutions were designed based on structural properties and other biological characteristics of residues to find the most effective amino acid on IFN affinity to advanced activities. The IFN-α2b mutants and receptors have been modeled and the interactions between two proteins have been studied as in silico by protein-protein docking for both mutants and native forms. The proper nucleic acid sequence IFN-α2 (T79Q) has been prepared based on the selected mutant. The modified IFN gene was cloned in pcDNA 3.1(-) and introduced to Chinese Hamster Ovary (CHO) cell line. Antiviral and antiproliferative assays of native and IFN-α2 (T79Q) proteins were performed in vitro. The results showed two-fold increasing in IFN-α2 (T79Q) activity (antiviral and antiproliferative activity) in comparison to native IFN-α2b. This engineered IFN-α2b may have significant novel therapeutic applications and in silico studies can be an influential method for practical research function and structure of these molecules.

Small Molecule Agonists for the Type I Interferon Receptor: An In Silico Approach

Type I interferons (IFNs) exhibit broad-spectrum antiviral activity, with potential utility against emerging acute virus infections that pose a threat to global health. Recombinant IFN-αs that have been approved for clinical use require cold storage and are administered through intramuscular or subcutaneous injection, features that are problematic for global distribution, storage, and administration. Cognizant that the biological potency of an IFN-α subtype is determined by its binding affinity to the type I IFN receptor, IFNAR, we identified a panel of small molecule nonpeptide compounds using an in silico screening strategy that incorporated specific structural features of amino acids in the receptor-binding domains of the most potent IFN-α, IFN alfacon-1. Hit compounds were selected based on ease of synthesis and formulation properties. In preliminary biological assays, we provide evidence that these compounds exhibit antiviral activity. This proof-of-concept study validates the strategy of in silico design and development for IFN mimetics.

The yin and yang of viruses and interferons

Interferons (IFNs)-α/β are critical effectors of the innate immune response to virus infections. Through activation of the IFN-α/β receptor (IFNAR), they induce expression of IFN-stimulated genes (ISGs) that encode antiviral proteins capable of suppressing viral replication and promoting viral clearance. Many highly pathogenic viruses have evolved mechanisms to evade an IFN response and the balance between the robustness of the host immune response and viral antagonistic mechanisms determines whether or not the virus is cleared. Here, we discuss IFNs as broad-spectrum antivirals for treatment of acute virus infections. In particular, they are useful for treatment of re-emerging virus infections, where direct-acting antivirals (DAAs) have limited utility due to DAA-resistant mutations, and for newly emerging virus strains in which the time to vaccine availability precludes vaccination at the onset of an outbreak.

De novo design of nonpeptidic compounds targeting the interactions between interferon-alpha and its cognate cell surface receptor

Type 1 interferons (IFN) bind specifically to the corresponding receptor, IFNAR. Agonists and antagonists for IFNAR have potential therapeutic value in the treatment of viral infections and systemic lupus erythematosus, respectively. Specific sequences on the surface of IFN, IFN receptor recognition peptides (IRRPs) mediate the binding and signal transduction when IFN interacts with IFNAR. Structural features of two such IRRPs, IRRP-1 and IRRP-3, were used as templates to design small molecule mimetics. In silico screening was used to identify the molecular structural features mimicking their surface characteristics. A set of 26 compounds were synthesized and their ability to interfere with IFN-IFNAR interactions was investigated. Two compounds exhibited antagonist activity, specifically, blocking IFN-inducible Stat phosphorylation Stat complex-DNA binding. Design principles revealed here pave the way toward a novel series of small molecules as antagonists for IFN-IFNAR interactions.

The human type I interferon receptor: NMR structure reveals the molecular basis of ligand binding

The potent antiviral and antiproliferative activities of human type I interferons (IFNs) are mediated by a single receptor comprising two subunits, IFNAR1 and IFNAR2. The structure of the IFNAR2 IFN binding ectodomain (IFNAR2-EC), the first helical cytokine receptor structure determined in solution, reveals the molecular basis for IFN binding. The atypical perpendicular orientation of its two fibronectin domains explains the lack of C domain involvement in ligand binding. A model of the IFNAR2-EC/IFNalpha2 complex based on double mutant cycle-derived constraints uncovers an extensive and predominantly aliphatic hydrophobic patch on the receptor that interacts with a matching hydrophobic surface of IFNalpha2. An adjacent motif of alternating charged side chains guides the two proteins into a tight complex. The binding interface may account for crossreactivity and ligand specificity of the receptor. This molecular description of IFN binding should be invaluable for study and design of IFN-based biomedical agents.

Site-specific lipophilic modification of interferon-alpha

Interferon-alpha (IFNalpha), a cytokine with modulatory activities on many cell types, is useful for treating many types of cancer and infectious diseases. This study investigates whether modification of a protein, using IFNalpha as an example, with a lipophilic group can alter its distribution and kinetic properties in the body. Ser163 of IFNalpha2a was mutated to Cys to generate a free sulfhydryl group for site-specific chemical modification. IFNalpha2a(S163C) was conjugated by iodoacetamide derivatives of varying lengths, and the modified IFNalpha2a was purified by gel filtration chromatography. The biological activities of IFNalpha2a(S163C) and lipophilized IFNalpha2a(S163C) were similar to that of IFNalpha2a, as evidenced by their inhibitory effects on the growth of Daudi cells and on the replication of vesicular stomatitis virus in Madin-Darby bovine kidney cells. Lipophilized IFNalpha2a(S163C) bound to human serum albumin and cell membranes more readily than did IFNalpha2a. Future experiments will investigate whether lipophilized IFNalpha2a(S163C) has improved pharmacokinetic properties.

New structural and functional aspects of the type I interferon-receptor interaction revealed by comprehensive mutational analysis of the binding interface

Type I interferons bind to two cell surface receptors, ifnar1 and ifnar2, as the first step in the activation of several signal transduction pathways that elicit an anti-viral state and an anti-proliferative response. Here, we quantitatively mapped the complete binding region of ifnar2 on interferon (IFN)alpha2 by 35 individual mutations to alanine and isosteric residues. Of the six "hot-spot" residues identified (Leu-30, Arg-33, Arg-144, Ala-145, Met-148, and Arg-149), four are located on the E-helix, which is located at the center of the binding site flanked by residues on the A-helix and the AB-loop. The contribution of residues of the D-helix, which have been previously implicated in binding, proved to be marginal for the interaction with the extracellular domain of ifnar2. Interestingly, the ifnar2 binding site overlaps the largest continuous hydrophobic patch on IFNalpha2. Thus, hydrophobic interactions seem to play a significant role stabilizing this interaction, with the charged residues contributing toward the rapid association of the complex. Relating the anti-viral and anti-proliferative activity of the various interferon mutants with their affinity toward ifnar2 results in linear function over the whole range of affinities investigated, suggesting that ifnar2 binding is the rate-determining step in cellular activation. Dose-time analysis of the anti-viral response revealed that shortening the incubation time of low-level activation cannot be compensated by higher IFN doses. Considering the strict dependence of the cellular response on affinity, these results suggest that for maintaining transcription of IFN-responsive genes over a longer time period, low but continuous signaling through the IFN receptor is essential.

Structure-function study of the extracellular domain of the human type I interferon receptor (IFNAR)-1 subunit

Despite accumulating information about the different effector molecules and signaling cascades that are invoked on interferon-alpha (IFN-alpha) binding to the type 1 IFN receptor, little is known about the specifics of the binding interactions between the ligand and the receptor complex. The IFN-alpha/beta receptor (IFNAR)-2 subunit of the IFN receptor is considered the primary binding chain of the receptor, yet it is clear that both receptor subunits, IFNAR-1 and IFNAR-2, cooperate in the high-affinity binding of IFN to the receptor complex. Earlier results from our laboratory suggested that an association of IFNAR-1 with membrane Galalpha1-4Gal-containing glycolipids facilitates receptor-mediated signaling. The data implicated amino acid residues in the SD100 domain of IFNAR-1 in the glycosphingolipid (GSL) modification of the type 1 IFN receptor. Interestingly, the human and murine counterparts of IFNAR-1 exhibit remarkable species specificity despite their considerable amino acid sequence identity. Certainly, those amino acid residues that effect GSL modification of IFNAR-1 are conserved between species, yet specific regions of IFNAR-1 that confer species specificity have not been defined. To delineate further the role of the IFNAR-1 SD100A domain in receptor function, a chimeric cDNA was assembled, in which the SD100A domain of the murine IFNAR-1 chain was replaced with the human sequence. This construct was expressed in IFNAR-1-/- mouse embryonic fibroblasts, and stable transfectants were established. Transfectants are fully sensitive to murine IFN-alpha4 treatment with respect to the induction of IFN-stimulated gene factor 3 (ISGF3) and sis-inducing factor (SIF) signal transducer and activator of transcription factor (Stat) complexes, exhibiting comparable levels of Stat activation to those observed in IFNAR-1-/- cells reconstituted with intact MuIFNAR-1. Similar results were obtained with IFN-induced antiviral and growth inhibitory responses. Viewed together, these data suggest that the SD100A domain of IFNAR-1 does not contribute to species-specific IFN binding.

Identification of a linear epitope of interferon-alpha2b recognized by neutralizing monoclonal antibodies

Four monoclonal antibodies (mAbs) directed against the recombinant human interferon-alpha2b (IFN-alpha2b) were used as probes to study the interaction of the IFN molecule to its receptors. The [125I]IFN-alpha2b binding to immobilized mAbs was completely inhibited by IFN-alpha2b and IFN-alpha2a but neither IFNbeta nor IFNgamma showed any effect. Gel-filtration HPLC of the immune complexes formed by incubating [125I]IFN-alpha2b with paired mAbs revealed the lack of simultaneous binding of two different antibodies to the tracer, suggesting that all mAbs recognize the same IFN antigenic domain. Furthermore, the mAbs were also able to neutralize the IFN-alpha2b anti-viral and anti-proliferative activities as well as [125I]IFN-alpha2b binding to WISH cell-membranes. As [125I]mAbs did not recognize IFN exposed epitopes in the IFN:receptor complexes, mAb induction of a conformational change in the IFN binding domain impairing its binding to receptors was considered unlikely. In order to identify the IFN region recognized by mAbs, IFN-alpha2b was digested with different proteolytic enzymes. Immunoreactivity of the resulting peptides was examined by Western blot and their sequences were established by Edman degradation after blotting to poly(vinylidene difluoride) membranes. Data obtained indicated that the smallest immunoreactive region recognized by mAbs consisted of residues 107-132 or 107-146. As this zone includes the sequence 123-140, which has been involved in the binding to receptors, and our mAbs did not show an allosteric behaviour, it is concluded that they are directed to overlapping epitopes located close to or even included in the IFN binding domain.

Divergence of Binding, Signaling, and Biological Responses to Recombinant Human Hybrid IFN

Three human IFN-α hybrids, HY-1 [IFN-α21a(1-75)/α2c(76-165)], HY-2 [IFN-α21a(1-95)/α2c(96-165)], and HY-3 [IFN-α2c(1-95)/α21a(96-166)], were constructed, cloned, and expressed. The hybrids had comparable specific antiviral activities on Madin-Darby bovine kidney (MDBK)3 cells but exhibited very different antiproliferative and binding properties on human Daudi and WISH cells and primary human lymphocytes. Our data suggest that a portion of the N-terminal region of the molecule is important for interaction with components involved in binding of IFN-α2b while the C-terminal portion of IFN is critical for antiproliferative activity. A domain affecting the antiproliferative activity was found within the C-terminal region from amino acid residues 75–166. The signal transduction properties of HY-2 and HY-3 were evaluated by EMSA and RNase protection assays. Both HY-2 and HY-3 induced activation of STAT1 and 2. However, HY-2 exhibited essentially no antiproliferative effects at concentrations that activated STAT1 and 2. Additionally, at concentrations where no antiproliferative activity was seen, HY-2 induced a variety of IFN-responsive genes to the same degree as HY-3. RNase protection assays also indicate that, at concentrations where no antiproliferative activity was seen for HY-2, this construct retained the ability to induce a variety of IFN-inducible genes. These data suggest that the antiproliferative response may not be solely directed by the activation of the STAT1 and STAT2 pathway in the cells tested.

Palmitoyl derivatives of interferon alpha: potential for cutaneous delivery

Palmitoyl derivatives of interferon alpha2b (p-IFNalpha) were prepared by covalent attachment of the fatty acid to lysine residues in the protein through a reaction with N-hydroxysuccinimide palmitate ester. The p-IFNalpha was characterized by capillary electrophoresis (CE), mass spectrometry (MS), SDS-PAGE, and antiviral assay. Flow-through diffusion cells and human breast skins were used to measure cutaneous and percutaneous absorption. Formation of p-IFNalpha derivatives was demonstrated by CE to be dependent on reaction time and reagent: protein ratio. Electrospray MS of the crude p-IFNalpha mixture indicated three populations of IFNalpha derivatives with 10, 11, and 12 palmitoyl substitutions. The addition of palmitoyl residues to IFNalpha under the conditions described reduced the antiviral specific activity by 50%. However, the cutaneous absorption of p-IFNalpha was about 5-6 times greater than the parent protein. The amount of p-IFNalpha and IFN alpha in whole skin after 24 h of treatment was 2.106 +/- 1.216 microg/cm2 and 0.407 +/- 0.108 microg/cm2, respectively. Approximately two times higher flux was detected for p-IFNalpha compared to the nonfatty acylated IFNalpha. The total amount of drug diffused in 24 h was also approximately two times higher for the p-IFNalpha. The results indicate a potential for using fatty acylated derivatives of IFN alpha for dermal and transdermal delivery.

Review of recent developments in the molecular characterization of recombinant alfa interferons on the 40th anniversary of the discovery of interferon

Recombinant alfa interferons (IFN-alpha s) are approved worldwide for the treatment of a variety of cancers and diseases of virologic origin. A series of recent advances in the molecular characterization of recombinant IFN-alpha s have allowed the determination of the three-dimensional IFN-alpha 2b structure by high-resolution x-ray crystallography. We review here recent developments in our understanding of the molecular and physicochemical properties of recombinant IFN-alpha, including our current state of knowledge of the IFN-alpha gene family and the multiple species of human leukocyte IFN. Based on the reported three-dimensional structure of IFN-alpha 2b, we propose a molecular model for the IFN-alpha 2b receptor complex and predict models for the naturally occurring subtypes IFN-alpha 1 and IFN-alpha 8, as well as the synthetic, non-naturally occurring consensus IFN. Such models provide molecular insights into the mechanism of action of IFN-alpha.

Differences in activity between alpha and beta type I interferons explored by mutational analysis

Type I interferon (IFN) subtypes alpha and beta share a common multicomponent, cell surface receptor and elicit a similar range of biological responses, including antiviral, antiproliferative, and immunomodulatory activities. However, alpha and beta IFNs exhibit key differences in several biological properties. For example, IFN-beta, but not IFN-alpha, induces the association of tyrosine-phosphorylated receptor components ifnar1 and ifnar2, and has activity in cells lacking the IFN receptor-associated, Janus kinase tyk2. To define the structural basis for these functional differences we produced human IFN-beta with point mutations and compared them to wild-type IFN-beta in assays that distinguish alpha and beta IFN subtypes. IFN-beta mutants with charged residues (N86K, N86E, or Y92D) introduced at two positions in the C helix lost the ability to induce the association of tyrosine-phosphorylated receptor chains and had reduced activity on tyk2-deficient cells. The combination of negatively charged residues N86E and Y92D (homologous with IFN-alpha8) increased the cross-species activity of the mutant IFN-betas on bovine cells to a level comparable to that of human IFN-alphas. In contrast, point mutations in the AB loop and D helix had no significant effect on these subtype-specific activities. A subset of these latter mutations did, however, reduce activity in a manner analogous to IFN-alpha mutations. The effects of these mutations on IFN-beta activity are discussed in the context of a family of related ligands acting through a common receptor and signaling pathway.

Interferons Alpha, Beta, and Omega

Interferon alpha (IFN-α) is a mixture of closely related proteins, termed “subtypes,” expressed from distinct chromosomal genes. Interferon β (IFN-β) is a single protein species and is molecularly related to IFN-α subtypes, although it is antigenically distinct from them. IFN omega (IFN-ω) is antigenically distinct from IFN-α and IFN-β but is molecularly related to both. The genes of three IFN subtypes are tandemly arranged on the short arm of chromosome 9. They are transiently expressed following induction by various exogenous stimuli, including viruses. They are synthesized from their respective mRNAs for relatively short periods following gene activation and are secreted to act, via specific cell surface receptors, on other cells. IFN-α subtypes are secreted proteins and as such are transcribed from mRNAs as precursor proteins, pre-IFN-α, containing N-terminal signal polypeptides of 23 hydrophobic amino acids (aa) mainly. Pre-IFN-β contains 187 aa, of which 21 comprise the N-terminal signal polypeptide and 166 comprise the mature IFN-β protein. IFN-ω contains 195 aa—the N-terminal 23 comprising the signal sequence and the remaining 172, the mature IFN-ω protein. At the C-terminus, the aa sequence of IFN-ω is six residues longer than that of IFN-α or IFN-β proteins. IFN-α, as a mixture of subtypes, and IFN-ω may be produced together following viral infection of null lymphocytes or monocytes/macrophages. The biological activities of IFNs are mostly dependent upon protein synthesis with selective subsets of proteins mediating individual activities. IFNs can also stimulate indirect antiviral and antitumor mechanisms, depending upon cellular differentiation and the induction of cytotoxic activity.

Elucidation of the basic three-dimensional structure of type I interferons and its functional and evolutionary implications

The scientific and personal backgrounds of the crystallographic elucidation of the three-dimensional structure of murine interferon-beta (Mu-IFN-beta) are described. This structure, elucidated in 1990, is still the only experimentally determined structure for type I IFNs. Model-building studies for various type I IFNs based on the Mu-IFN-beta structure and the arguments on the receptor-binding epitopes appearing since then are reviewed. An updated set of a table and a figure demonstrating a strong correlation between the degree of amino acid sequence variation in various cytokine proteins and that in their cognate receptor proteins is given. The origin of a remarkably larger rate of evolutionary change in amino acid sequences of cytokine proteins despite their physiologic significance is discussed in view of the cytokine network and the neutral theory of evolution.

Structure-activity of type I interferons

Type I IFNs constitute a family of proteins exhibiting high homology in primary, secondary, and tertiary structures. They interact with the same receptor and transmit signals to cellular nucleus through a similar mechanism, eliciting roughly homogeneous biological activity. Nevertheless, the members of that family, IFN alpha species, IFN beta and IFN omega, due to local differences in the structure sometime show distinct properties. From the reported data it results that even minute changes or differences in the primary sequences could be responsible for a significant variety of biological actions, thus inducing to the hypothesis that Type I IFNs, rather than to be the result of a redundant replication during the evolution play definite roles in the defense of living organisms to foreign agents.

Zinc mediated dimer of human interferon-alpha 2b revealed by X-ray crystallography

BACKGROUND

The human alpha-interferon (huIFN-alpha) family displays broad spectrum antiviral, antiproliferative and immunomodulatory activities on a variety of cell types. The diverse biological activities of the IFN-alpha's are conveyed to cells through specific interactions with cell-surface receptors. Despite considerable effort, no crystal structure of a member of this family has yet been reported, because the quality of the protein crystals have been unsuitable for crystallographic studies. Until now, structural models of the IFN-alpha's have been based on the structure of murine IFN-beta (muIFN-beta). These models are likely to be inaccurate, as the amino acid sequence of muIFN-beta differs significantly from the IFN-alpha's at proposed receptor-binding sites. Structural information on a huIFN-alpha subtype would provide an improved basis for modeling the structures of the entire IFN-alpha family.

RESULTS

The crystal structure of recombinant human interferon-alpha 2b (huIFN-alpha 2b) has been determined at 2.9 A resolution. HuIFN-alpha 2b exists in the crystal as a noncovalent dimer, which associates in a novel manner. Unlike other structurally characterized cytokines, extensive interactions in the dimer interface are mediated by a zinc ion (Zn2+). The overall fold of huIFN-alpha 2b is most similar to the structure of muIFN-beta. Unique to huIFN-alpha 2b is a 3(10) helix in the AB loop which is held to the core of the molecule by a disulfide bond.

CONCLUSIONS

The structure of huIFN-alpha 2b provides an accurate model for analysis of the > 15 related type 1 interferon molecules. HuIFN-alpha 2b displays considerable structural similarity with muIFN-beta, interleukin-10 and interferon-gamma, which also bind related class 2 cytokine receptors. From these structural comparisons and numerous studies on the effects of mutations on biological activity, we have identified protein surfaces that appear to be important in receptor activation. This study also reveals the potential biological importance of the huIFN-alpha 2b dimer.

Refolding, isolation and characterization of crystallizable human interferon-alpha 8 expression in Saccharomyces cerevisiae

Human interferon-alpha 8 was expressed in Saccharomyces cerevisiae and found to accumulate intracellularly in an insoluble form. The protein could be solubilized and converted to a biologically active form with high yield by a denaturation-refolding procedure. The interferon-alpha 8 was further purified to apparent homogeneity by copper-chelate affinity chromatography and anion-exchange chromatography and fully characterized by sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE), N-terminal sequence analysis, mass spectrometry, circular-dichroism (CD) spectroscopy and specific activity. Secondary-structure predictions from CD spectroscopy indicate that the molecule is correctly folded. Peptide mapping supported the correct sequence and the expected disulfide-bridge connectivity. The purified protein elutes on reversed-phase high-pressure liquid chromatography (RP-HPLC) as two peaks. Electrospray mass spectrometry and N-terminal sequence analysis of the minor component indicated the existence of an N-terminal acetyl group for the later eluting HPLC-component. In anti-viral assays, the two IFN forms were equally active. Hexagonal crystals of this interferon preparation could be obtained. On the basis of the electrophoretic mobility, HPLC profile, and biological activity assay, the crystalline material was judged to be identical to the uncrystallized interferon. Interferon in crystallized form was found to be stable for up to 24 months and, therefore, could be used for long-term storage, particularly for material intended for clinical use.

The biologic activity and molecular characterization of a novel synthetic interferon-alpha species, consensus interferon

Consensus interferon (Infergen) is a wholly synthetic type I interferon (IFN), developed by scanning several interferon-alpha nonallelic subtypes and assigning the most frequently observed amino acid in each position, resulting in a consensus sequence. The antiviral, antiproliferative, NK cell activation activity, cytokine induction, and interferon-stimulated gene-induction activity of consensus interferon has been compared with naturally occurring type I interferons. In all of these comparisons, consensus interferon had a higher activity when compared, on a mass basis, with IFN-alpha 2a and IFN-alpha 2b, although the activity was the same for all of these parameters on an antiviral unit basis. That a synthetic type I interferon could have higher activities than naturally occurring molecules is surprising and may be a result of the higher affinity for the array of type I interferon receptors demonstrated for consensus interferon when compared with IFN-alpha. In contrast, consensus interferon was shown to be an inferior inducer of IL-1 beta when compared with IFN-alpha. These results may reflect differential binding to multiple accessory proteins interacting with a type I interferon receptor. These unique biologic properties may lead to a favorable clinical benefit for consensus interferon when compared with the naturally occurring recombinant molecules. Ongoing clinical trials will ascertain whether consensus interferon can be used in a wide array of disease situations, such as chronic viral infections and certain malignancies.

Cloning and biologic activities of a bovine interferon-alpha isolated from the epithelium of a rotavirus-infected calf

A cDNA encoding a distinct bovine (Bo) interferon (IFN) alpha, designated BoIFN-alpha E, was generated from gut epithelial cells isolated from a rotavirus-infected calf. The BoIFN-alpha E cDNA sequence shared a greater than 90% identity with the other BoIFN-alpha subtypes. The cDNA encoding BoIFN-alpha E has been expressed in insect cells using the baculovirus Autographa californica nuclear polyhedrosis virus (AcMNPV) as a vector. Insect cells infected with recombinant virus secreted a protein with a relative molecular mass of 19,500 into the culture medium not observed in cells infected with wild-type AcMNPV. Supernatants harvested from cultures of insect cells infected with the recombinant AcMNPV encoding IFN-alpha E inhibited the replication of Semliki Forest virus in a bovine cell line and typically showed 10(6) dilution units/ml of antiviral activity. However, differences were observed between the activities of recombinant BoIFN-alpha E and BoIFN-alpha 1 1 on the proliferation of WC1+ gamma/delta T cells. Purified ( > 99%) WC1+ gamma/delta T cells failed to proliferate to IFN-alpha 1 1 or concanavalin A and IFN-alpha E acted as a weak proliferative signal to these cells, demonstrating a functional difference between two closely related BoIFN-alpha subtypes.

A three-dimensional model of interferon-tau

The interferon-tau (IFN-tau) are type I IFN whose expression is restricted to the embryonic trophectoderm of the developing placenta of ruminant ungulate species, where they act as hormones of pregnancy. Here computer modeling has been used to generate homology models of bovine and ovine IFN-tau based on the refined crystal structure of murine IFN-beta. The IFN-tau structure, like that of MuIFN-beta, is based on five long alpha helices (A-E), one short helix in the middle of the loop connecting helices C and D and a long loop between helices A and B. BoIFN-tau differs from MuIFN-beta in three important respects. First, as in all IFN-tau, there is a carboxyl tail of nine amino acids that cannot be accurately modeled but that would have a length of approximately 30 A when fully extended. Second, like the IFN-alpha subtype, all IFN-tau have a three-amino acid insertion in loop AB and a likely disulfide bridge between Cys29 and Cys139 that lead to marked conformational differences between them and MuIFN-beta in a region (Leu22 to Arg33 in IFN-tau) believed to interact with the receptor. Third, all IFN-tau, as well as the related IFN-omega, possess a Gly at position 126 (rather than the equivalent Arg on MuIFN-beta and IFN-alpha) that will impair an extensive hydrogen bonding interaction between helix D and loop AB. As a result, the polypeptide segment around this region (Phe36 to Gln40) of loop AB is likely to be considerably more flexible than in other type I IFN.

The evolution of the type I interferon gene family in mammals

A phylogenetic analysis of mammalian type I interferon (IFN) genes showed: (1) that the three main subfamilies of these genes in mammals (IFN-beta, IFN-alpha, and IFN-omega) diverged after the divergence of birds and mammals but before radiation of the eutherian orders and (2) that IFN-beta diverged first. Although apparent cases of interlocus recombination among mouse IFN-alpha genes were identified, the hypothesis that coding regions of IFN-alpha genes have been homogenized within species by interlocus recombination was not supported. Flanking regions as well as coding regions of IFN-alpha were more similar within human and mouse than between these species; and reconstruction of the pattern of nucleotide substitution in IFN-alpha coding regions of four mammalian species by the maximum parsimony method suggested that parallel substitutions have occurred far more frequently between species than within species. Therefore, it seems likely that IFN-alpha genes have duplicated independently within different eutherian orders. In general, type I IFN genes are subject to purifying selection, which in the case of IFN-alpha and IFN-beta is strongest in the putative receptor-binding domains. However, analysis of the pattern of nucleotide substitution among IFN-omega genes suggested that positive Darwinian selection may have acted in some cases to diversify members of this subfamily at the amino acid level.

Configuration of the interferon-alpha/beta receptor complex determines the context of the biological response

Constituents of the Type 1 interferon (IFN) receptor (IFNABR) identified to date include the alpha and beta transmembrane subunits and the associated intracellular kinases, Jak 1 and Tyk 2. In this report, we demonstrate that a human cell type that expresses both subunits of IFNABR, together with Jak 1 and Tyk 2, exhibits a limited binding capacity for and is only partially sensitive to the effects of IFN-alpha/beta, despite adequate levels of the cytoplasmic transcription factors Stat1, Stat2, and Stat3. Specifically, a low affinity interaction between IFN-alpha/beta and cell surface receptors results in ISGF3 (Stat1:2) activation and an antiviral response, yet no IFN-inducible growth inhibition. Using a panel of murine cells that are variably configured with respect to the human IFNABR-alpha/beta subunits, we provide evidence that an additional component(s) encoded on human chromosome 21 is required to confer high affinity binding and IFN-inducible growth inhibition to cells that express the alpha and beta subunits of the IFNABR. The data indicate that transcriptional activation that leads to an antiviral response is mediated by IFN-alpha/beta activation of IFNABR-alpha and IFNABR-beta in the context of a low affinity interaction, yet a high affinity interaction is necessary for signal transducing events that mediate growth inhibition. We provide evidence that the extent of ISGF3 activation correlates directly with the magnitude of an antiviral but not a growth inhibitory response.

Isolation, properties and chromosomal localization of four closely linked hamster interferon-alpha-encoding genes

Three recombinant phages containing hamster interferon-alpha-encoding genes (Ha Ifa) were isolated from a Ha genomic library, using a murine (Mu) Ifa probe. The phage inserts contained overlapping genomic fragments which span a total length of approx. 30 kb, on which four Ha Ifa genes are localized. The Ifa gene cluster could be assigned to hamster chromosome 2q. The nt sequences of the four Ifa genes were determined. Two of the genes are functional (Ha Ifa-1 and Ifa-3) and two are pseudogenes (Ifa-ps2 and Ifa-ps4). Ha Ifa-1 and -3 were transiently expressed in COS cells and they gave rise to protein products (A1 and A3, respectively) with antiviral properties on hamster CHO cells. In addition, Ha A1 revealed high antiviral activity on murine L929 cells.

Interferon-alpha hybrids

The alpha-interferons (IFN-alpha) belong to a family of polypeptides comprising several subtypes. Using recombinant DNA technology, it has been possible to create IFN hybrids that provide novel combinations of the amino acid residues from the parental protein sequences. They have been used to study structure-activity relationships of IFN-alpha and interactions with the IFN-alpha receptor, and to create analogs of natural IFNs with novel properties for potential therapeutic application. The biological data obtained with these hybrids are now evaluated in terms of the published structural and homology models of IFN-beta and -alpha.

Chicken interferon gene: cloning, expression, and analysis

A gene encoding chicken interferon (ChIFN) was cloned from a cDNA library made from primary chick embryo cells that had been "aged" in vitro so as to produce copious amounts of IFN upon induction. The coding region is predicted to produce a signal peptide of 31 amino acids and a mature protein of 162 amino acids with a molecular weight of 18,957. There are four potential N-glycosylation sites and six cysteine residues. Three disulfide bonds are possible, with two being common to most mammalian type I IFNs. A motif of 10 amino acids surrounding Cys-137 is highly conserved: It shows 80% homology with mammalian type I IFNs, but only 30% with a reported fish IFN. The T-rich 3' UTR displays the canonical element AATAAA required for polyadenylation, and contains six repeats of the octamer CTATTTAT that may be involved in down-regulating translation. Northern blots demonstrate that the accumulation of ChIFN mRNA correlates with induction of ChIFN determined by bioassay. Biologically active protein was synthesized in transfected mouse L cells using mRNA prepared in vitro from the cloned sequence. This activity was neutralized by a monoclonal antibody prepared against purified ChIFN. The ChIFN gene shows sequence identity at the amino acid/nucleotide level with consensus mammalian IFNs as follows: alpha (24/23%), beta (20/24%), omega (23/43%), tau (20/43%), gamma (3/31%), and with flatfish IFN (16/35%). The conserved features of the predicted ChIFN protein and the general similarity of predicted secondary structure suggest a molecule that fits the five alpha-helix three-dimensional topology reported for type I mammalian IFNs.(ABSTRACT TRUNCATED AT 250 WORDS)