Macrophage Migration Inhibitory Factor: Identification of the 30-kDa MIF-Related Protein in Bovine Brain

Macrophage migration inhibitory factor (MIF) is a ubiquitous protein playing various immunologic, enzymatic, and hormonal roles. MIF was originally identified for its capacity to inhibit the random movement of macrophages in vitro. MIF is widely expressed in many tissues with particularly high levels in the nervous system. Using the reversed-phase HPLC, N-terminal microsequence analysis, and database searching, we have identified in bovine brain several MIF-like proteins. According to mass spectral analysis, the molecular masses for three of them were determined as 12,369.2, 12,299.7, and 9,496.2 Da. In addition, we have identified another MIF-related protein (29,568.9 Da) by Western blotting using anti-MIF antibody raised to MIF (having an apparent molecular weight of 12 kDa) isolated to homogeneity from bovine brain cytosol. The modified purification procedure was mainly based on exclusion- and ion-exchange chromatography. Using p-hydroxyphenylpyruvic acid as a substrate, we have demonstrated tautomerase activity of the isolated MIF. The N-terminal sequences for all MIF-like proteins were found to be identical. Several other higher molecular weight putative MIF-related proteins were also revealed in the bovine brain cytosol extract. A multifunctional nature of MIF is suggested to be a result of its occurrence in different oligomerization states in a wide variety of tissues and cells.     

Macrophage migration inhibitory factor: Isolation from bovine brain

The purification of macrophage migration inhibitory factor (MIF) from bovine brain cytosol and its partial characterization are reported. A rapid and relatively simple method for MIF isolation was developed based mainly on size-exclusion chromatography on Toyopearl TSK polymer having a tendency to adsorb MIF as compared to elution of other proteins with similar molecular weights. The method gives a high yield of MIF (0.1 mg homogenous protein per g wet tissue). The retardation is conveniently utilized to achieve good separations of MIF from other proteins of similar molecular weights. The isolated protein was identified as MIF by SDS-electrophoresis, immunoblotting, sequencing of the N-terminal amino acid residues, and also by determination of keto-enol tautomerase activity that is characteristic of MIF with p-hydroxyphenylpyruvic acid as a substrate.     

Direct Modification of the Proinflammatory Cytokine Macrophage Migration Inhibitory Factor by Dietary Isothiocyanates

Isothiocyanates are a class of phytochemicals with widely reported anti-cancer and anti-inflammatory activity. However, knowledge of their activity at a molecular level is limited. The objective of this study was to identify biological targets of phenethyl isothiocyanate (PEITC) using an affinity purification approach. An analogue of PEITC was synthesized to enable conjugation to a solid-phase resin. The pleiotropic cytokine macrophage migration inhibitory factor (MIF) was the major protein captured from cell lysates. Site-directed mutagenesis and mass spectrometry showed that PEITC covalently modified the N-terminal proline residue of MIF. This resulted in complete loss of catalytic tautomerase activity and disruption of protein conformation, as determined by impaired recognition by a monoclonal antibody directed to the region that receptors and interacting proteins bind to MIF. The conformational change was supported by in silico modeling. Monoclonal antibody binding to plasma MIF was disrupted in humans consuming watercress, a major dietary source of PEITC. The isothiocyanates have significant potential for development as MIF inhibitors, and this activity may contribute to the biological properties of these phytochemicals.     

Dissection of the enzymatic and immunologic functions of macrophage migration inhibitory factor. Full immunologic activity of N-terminally truncated mutants.

Macrophage migration inhibitory factor (MIF) is a cytokine with broad regulatory functions in innate immunity. MIF belongs to the few cytokines displaying catalytic activities, i.e. MIF has a Pro2-dependent tautomerase and a Cys-Ala-Leu-Cys (CALC) cysteine-based thiol-protein oxidoreductase activity. Previous studies have addressed the roles of the catalytic site residues and the C-terminus. The two activities have not been directly compared. Here we report on the N-terminal mutational analysis and minimization of MIF and on a dissection of the two catalytic activities by comparing mutants P2AMIF, Delta4MIF, Delta5MIF, Delta6MIF, Delta7MIF, Delta8MIF, and Delta10MIF with the cysteine mutants of MIF. As N-terminal deletion was predicted to interfere with protein structure due to disruption of the central beta sheet, it was surprising that deletion of up to six N-terminal residues resulted in normally expressed proteins with wild-type conformation. Strikingly, such mutants exhibited full MIF-specific immunologic activity. While mutation of Pro2 eliminated tautomerase activity, the CALC cysteine residues had no influence on this activity. However, mutant C81SMIF, which otherwise has full biologic activity, only had 32% tautomerase activity. Deletion of four N-terminal residues did not interfere with insulin reduction by MIF. By contrast, reduction of 2-hydroxyethyldisulfide (HED) was markedly affected by N-terminal manipulation, with P2AMIF and Delta2MIF exhibiting 40% activity, and Delta4MIF completely failing to reduce HED. This study constitutes the first comparison of the two catalytic activities of MIF and should assist in understanding the molecular links between the catalytic and immunologic activities of this cytokine and in providing guidelines for N-terminal protein minimization.     

Charge Heterogeneity of Bovine Brain Macrophage Migration Inhibitory Factor

Macrophage migration inhibitory factor (MIF) is known as a ubiquitous pluripotent cytokine originally identified for its capacity to inhibit the random migration of macrophages in vitro. It is recognized as an important regulator of the immunological, neuroendocrine and enzymatic processes. MIF is widely expressed in brain, but its role in the nervous system is not yet understood. In the course of the study of the primary structure of bovine brain MIF we have previously identified a number of MIF-related proteins having identical N-terminal sequences. In this paper we report the results of isoelectric focusing of MIF isolated to a homogeneous state from bovine brain that revealed MIF charge heterogeneity. We have detected isoelectric forms of MIF with pI values of 6.9, 7.0, 7.3, and 7.8. The diverse actions of MIF within the immuno-neuroendocrine system is suggested to be a result of its occurrence in different isoforms and oligomerization states.     

Two human trypsinogens. Purification, molecular properties, and N-terminal sequences

The two human trypsinogens have been isolated from human pancreatic juice in a sufficient amount to study molecular and structural properties. The purification procedure included filtration on Sephadex G-100 followed by ion-exchange chromatography on DEAE-cellulose. The two trypsinogens represent 19% of total proteins of pancreatic juice. Trypsinogen 1, the major form, is present in a quantity twice that of trypsinogen 2, which is the most anionic protein in human pancreatic juice. The two proteins have partial immunological identity, close molecular weights (23 438 and 25 006 for trypsinogens 1 and 2, respectively) and similar amino acid compositions. The N-terminal sequences are the same for the first 9 residues: Ala-Pro-Phe-Asp4-Lys-Ile. The two proteins differ in the activation peptides released during the transformation to trypsins. Trypsinogen 2 liberates one octapeptide Ala-Pro-Phe-Asp4-Lys while trypsinogen 1 liberates two peptides, the same octapeptide and the pentapeptide (Asp)4-Lys.     

Internal dynamics and ionization states of the macrophage migration inhibitory factor: comparison between wild-type and mutant forms

The macrophage migration inhibitory factor (MIF) is a cytokine that shares a common structural architecture and catalytic strategy with three isomerases: 4-oxalocrotonate tautomerase, 5-carboxymethyl-2-hydroxymuconate isomerase, and D-dopachrome tautomerase. A highly conserved N-terminal proline acts as a base-acid during the proton transfer reaction catalyzed by these enzymes. Such unusual catalytic strategy appears to be possible only due to the N-terminal proline pK(a) shifted to 5.0-6.0 units. Mutations of this residue result in a significant decrease of the catalytic activity of MIF. Two hypotheses have been proposed to explain the catalytic inefficiency of MIF: the lower basicity of primary amines with regard to secondary ones and the increased flexibility resulting from the replacement of a proline by residues like glycine. To investigate that, we have performed molecular dynamics simulations of MIF wild-type and its mutant P1G, as well as calculated the protonation properties of several mutant forms. It was found that the N-terminal glycine does not show larger fluctuations compared to proline, but the former residue is more exposed to the solvent throughout the simulations. The apparent pK(a) of these residues displays very little change (as expected from the structural rigidity of MIF) and is not significantly affected by the surrounding ionizable residues. Instead, the hydrophobic character of the active site seems to be the main factor in determining the pKa of the N-terminal residue and the catalytic efficiency of MIF.     

Recombinant wheat antifungal PR4 proteins expressed in Escherichia coli.

PR proteins are soluble and host-coded molecules with antifungal activity induced by a variety of agents. Wheat contains several PR proteins and among them are those of the class 4 coded wheatwin1 and wheatwin2; the two native proteins have been isolated from wheat kernel and the coding cDNA clones have been recently characterized. Herein, we report the expression of recombinant wheatwin1 and wheatwin2 in Escherichia coli-insoluble fractions; a new protocol for the purification in high yields and correct processing of the two proteins was developed. The recombinant proteins have molecular weights identical to that of the native proteins, indicating that the removal of the N-terminal methionine and cyclization of glutamine to pyroglutamate was complete. Both recombinant proteins inhibited in vitro the growth of Fusarium culmorum exhibiting antifungal properties similar to those of the native proteins.     

Purification and characterization of the lytic activity induced by the prolate-headed bacteriophage P001 in Lactococcus lactis

The lytic activity induced by the lactococcal bacteriophage P001 was isolated from phage lysates of Lactococcus lactis by a four-step purification procedure. Two proteins lytic for L. lactis were identified with molecular weights of 28 kDA and 8 kDa, respectively. The N-terminal amino acid sequences of the two proteins were determined and degenerated oligonucleotide probes corresponding to these sequences were synthesized. DNA hybridization experiments with phage P001-DNA and lactococcal DNA revealed that both proteins were apparently encoded by a single lysin gene located on the phage P001 genome. This was confirmed by alignment of the determined N-terminal amino acid sequences with nucleotide sequences which were deduced from cloned Lactococcus bacteriophage lysin genes.     

Homologues of human macrophage migration inhibitory factor from a parasitic nematode. Gene cloning,protein activity,and crystal structure

Cytokines are the molecular messengers of the vertebrate immune system, coordinating the local and systemic immune responses to infective organisms. We report here functional and structural data on cytokine-like proteins from a eukaryotic pathogen. Two homologues of the human cytokine macrophage migration inhibitory factor (MIF) have been isolated from the parasitic nematode Brugia malayi. Both molecules (Bm-MIF-1 and Bm-MIF-2) show parallel functions to human MIF. They are chemotactic for human monocytes and activate them to produce IL-8, TNF-alpha, and endogenous MIF. The human and nematode MIF homologues share a tautomerase enzyme activity, which is in each case abolished by the mutation of the N-terminal proline residue. The crystal structure of Bm-MIF-2 at 1.8-A resolution has been determined, revealing a trimeric assembly with an inner pore created by beta-stranded sheets from each subunit. Both biological activity and crystal structure reveal remarkable conservation between a human cytokine and its parasite counterpart despite the considerable phylogenetic divide among these organisms. The strength of the similarity implies that MIF-mediated pathways play an important role in nematode immune evasion strategies.     

A Leishmania ortholog of macrophage migration inhibitory factor modulates host macrophage responses

Parasitic organisms have evolved specialized strategies to evade immune defense mechanisms. We describe herein an ortholog of the cytokine, macrophage migration inhibitory factor (MIF), which is produced by the obligate intracellular parasite, Leishmania major. The Leishmania MIF protein, Lm1740MIF, shows significant structural homology with human MIF as revealed by a high-resolution x-ray crystal structure (1.03 A). Differences between the two proteins in the N-terminal tautomerization site are evident, and we provide evidence for the selective, species-specific inhibition of MIF by small-molecule antagonists that target this site. Lm1740MIF shows significant binding interaction with the MIF receptor, CD74 (K(d) = 2.9 x 10(-8) M). Like its mammalian counterpart, Lm1740MIF induces ERK1/2 MAP kinase activation in a CD74-dependent manner and inhibits the activation-induced apoptosis of macrophages. The ability of Lm1740MIF to inhibit apoptosis may facilitate the persistence of Leishmania within the macrophage and contribute to its evasion from immune destruction.     

Partial purification of guinea pig MIF by affinity column chromatography using macrophages.

First we have confirmed the previous observation that the macrophage migration inhibitory factor (MIF) was adsorbed on normal peritoneal macrophages when they were incubated at 4 C for 60 min. It was found that macrophages fixed with 2% glutaraldehyde gave more reproducible results than viable cells in terms of "adsorption" of guinea pig MIF. The adsorption was achieved more completely at 37 C than at 4 C, indicating that this reaction is a temperature-dependent phenomenon. Using these glutaraldehyde-fixed macrophages, a kind of cell-affinity column was successfully developed. The guinea pig MIF preparation lost its activity when it was passed through this affinity column, and MIF adsorbed on the column was recovered by elution with 0.1 M (L)-fucose of 0.1 M (D)-glucose. Such MIF active eluate was found to be at least 30--40 fold more pure than the original MIF preparation which had been previously fractionated according to its molecular weight. Therefore, this type of macrophage-affinity column may be useful for the purification of MIF.     

Proteolytic hydrolysis and purification of the LRP/alfa-2-macroglobulin receptor domain from alpha-macroglobulins

A new, easier and efficient purification method, using Sephacryl and DEAE-Sephacel, of the C-terminal fragment of two alpha-macroglobulins, alpha(2)-M and PZP, is presented. Two larger peptides were identified for each protein as the C-terminal fragment, with molecular weights of approximately 30 kDa and the N-terminal sequences were determined to be SSTQDTV for alpha(2)-M and VALHLS for PZP. The smaller peptides with molecular weights of 18 kDa correspond to a shorter C-terminal sequence of these proteins, and they were determined to be EEFPFA for alpha(2)-M and ALKVQTV for PZP, with no interfering sequences detected. The results confirmed the discriminatory capacity of the purification procedure and the purity of the fragments. This new methodology facilitates biological studies of alpha-macroglobulins, and will enable elucidation of the role the C-terminal region may exert to eliminate alpha-macroglobulin-proteinases complexes from the circulation by the LRP/receptor.     

Recombinant Wheat Antifungal PR4 Proteins Expressed in Escherichia coli

PR proteins are soluble and host-coded molecules with antifungal activity induced by a variety of agents. Wheat contains several PR proteins and among them are those of the class 4 coded wheatwin1 and wheatwin2; the two native proteins have been isolated from wheat kernel and the coding cDNA clones have been recently characterized. Herein, we report the expression of recombinant wheatwin1 and wheatwin2 in Escherichia coli-insoluble fractions; a new protocol for the purification in high yields and correct processing of the two proteins was developed. The recombinant proteins have molecular weights identical to that of the native proteins, indicating that the removal of the N-terminal methionine and cyclization of glutamine to pyroglutamate was complete. Both recombinant proteins inhibited in vitro the growth of Fusarium culmorum exhibiting antifungal properties similar to those of the native proteins.     

An alternative use of basic pGEX vectors for producing both N- and C-terminal fusion proteins for production and affinity purification of antibodies

Glutathione S-transferase (GST) fusion proteins are widely used in protein production for pure immunogens, protein-protein, and DNA-protein interaction studies. Using basic pGEX vectors, foreign DNA is introduced to the C-terminus of the GST gene and the produced fusion proteins are C-terminally orientated. However, because the orientation of foreign polypeptides may have a very important role in the correct folding of the produced polypeptides, N-terminal fusion proteins are needed to express especially the N-terminus of the foreign polypeptide. Here, we introduce a novel use of the basic pGEX vectors for the production of N-terminal fusion proteins. In this procedure, PCR generated DNA fragments were cloned into the N-terminus of the GST gene in a unique EcoNI site located down-stream of the ATG initiation codon. The N-terminal fusion proteins were expressed in high quantities, easily solubilized, and affinity purified using our modification of current purification protocols. We also introduce here a new modification of the affinity purification of antibodies using covalently crosslinked GST and fusion proteins to glutathione-agarose beads. Our procedure was tested successfully for producing antibodies against both N- and C-terminus of the luteinizing hormone/chorionic gonadotropin receptor.     

Separation and some properties of the major proteins of the human erythrocyte membrane

A fractionation procedure is described which allows the isolation of three major human erythrocyte membrane proteins. Their isolation involves three sequential extraction procedures followed by gel filtration in 1% sodium dodecyl sulphate and preparative gel electrophoresis. All three proteins can be isolated from a single preparation. One of the proteins is the erythrocyte sialoglycoprotein, for which no C- or N-terminal residues were found. The other two proteins, which have not previously been isolated, have subunit molecular weights of 74000 and 93000 and contain 9 and 7% carbohydrate respectively. These glycoproteins have blocked N-terminal residues and show similarities in their chemical properties. Preparations derived from blood-group O erythrocytes contain no N-acetylgalactosamine, but similar preparations from blood-group A erythrocytes do contain this sugar. These three proteins cannot easily be solubilized by gentle aqueous procedures and represent about half of the erythrocyte ;ghost' protein. They carry a large proportion of the cell-surface carbohydrate.     

Enzymatically inactive macrophage migration inhibitory factor inhibits monocyte chemotaxis and random migration.

Macrophage migration inhibitory factor (MIF) is a cytokine that was first described as an inhibitor of the random migration of monocytes and macrophages and has since been proposed to have a number of immune and catalytic functions. One of the functions assigned to MIF is that of a tautomerase that interconverts the enol and keto forms of phenylpyruvate and (p-hydroxyphenyl)pyruvate and converts D-dopachrome, a stereoisomer of naturally occurring L-dopachrome, to 5,6-dihydroxyindole-2-carboxylic acid. The physiological significance of the MIF enzymatic activity is unclear. The three-dimensional structure of MIF is strikingly similar to that of two microbial enzymes (4-oxalocrotonate tautomerase and 5-carboxymethyl-2-hydroxymuconate isomerase) that otherwise share little sequence identity with MIF. MIF and these two enzymes have an invariant N-terminal proline that serves as a catalytic base. Here we report a new biological function for MIF, as an inhibitor of monocyte chemoattractant protein 1- (MCP-1-) induced chemotaxis of human peripheral blood monocytes. We find that MIF inhibition of chemotaxis does not occur at the level of the CC chemokine receptor for MCP-1, CCR2, since MIF does not alter the binding of (125)I-MCP-1 to monocytes. The role of MIF enzymatic activity in inhibition of monocyte chemotaxis and random migration was studied with two MIF mutants in which the N-terminal proline was replaced with either a serine or a phenylalanine. Both mutants remain capable of inhibiting monocyte chemotaxis and random migration despite significantly reduced or no phenylpyruvate tautomerase activity. These data suggest that this enzymatic activity of MIF does not play a role in its migration inhibiting properties.     

Identification of Parvalbumin Alpha in Bovine Hypothalamus: A Partial Primary Structure

In the course of the study of structure-functional properties and molecular mechanisms of neuropeptides and of low molecular weight proteins of the central nervous system we succeeded in isolating from the soluble fraction of bovine hypothalamus a protein having Mr 11897.3, according to mass spectral analysis. The purification procedure was mainly based on reversed phase HPLC. As the N-terminus of the molecule was found to be blocked, we have subjected it to CNBr degradation. By Edman microsequence analysis of the peptide fragments and by data base searching the isolated substance was identified as parvalbumin alpha (PRVA)—one of the calcium-binding proteins. However, its primary structure was found not to be identical to that of the known PRVAs from other sources. One of the features of PRVA is its stability. Being subjected to an exhausting purification procedure it retains its complete structure. As neuropeptides and low molecular weight proteins are found to be polyfunctional, a central question concerns the biological role of PRVAs in terms of where and when they express their action.     

Structural and functional analysis of the three MIF4G domains of nonsense-mediated decay factor UPF2

Nonsense-mediated decay (NMD) is a eukaryotic quality control pathway, involving conserved proteins UPF1, UPF2 and UPF3b, which detects and degrades mRNAs with premature stop codons. Human UPF2 comprises three tandem MIF4G domains and a C-terminal UPF1 binding region. MIF4G-3 binds UPF3b, but the specific functions of MIF4G-1 and MIF4G-2 are unknown. Crystal structures show that both MIF4G-1 and MIF4G-2 contain N-terminal capping helices essential for stabilization of the 10-helix MIF4G core and that MIF4G-2 interacts with MIF4G-3, forming a rigid assembly. The UPF2/UPF3b/SMG1 complex is thought to activate the kinase SMG1 to phosphorylate UPF1 in vivo. We identify MIF4G-3 as the binding site and in vitro substrate of SMG1 kinase and show that a ternary UPF2 MIF4G-3/UPF3b/SMG1 complex can form in vitro. Whereas in vivo complementation assays show that MIF4G-1 and MIF4G-2 are essential for NMD, tethering assays reveal that UPF2 truncated to only MIF4G-3 and the UPF1-binding region can still partially accomplish NMD. Thus UPF2 MIF4G-1 and MIF4G-2 appear to have a crucial scaffolding role, while MIF4G-3 is the key module required for triggering NMD.