Preparative Scale Production of Recombinant Human Transthyretin for Biophysical Studies of Protein-Ligand and Protein-Protein Interactions

Human transthyretin (hTTR), a serum protein with a main role in transporting thyroid hormones and retinol through binding to the retinol-binding protein, is an amyloidogenic protein involved in familial amyloidotic polyneuropathy (FAP), familial amyloidotic cardiomyopathy, and central nervous system selective amyloidosis. hTTR also has a neuroprotective role in Alzheimer disease, being the major Aβ binding protein in human cerebrospinal fluid (CSF) that prevents amyloid-β (Aβ) aggregation with consequent abrogation of toxicity. Here we report an optimized preparative expression and purification protocol of hTTR (wt and amyloidogenic mutants) for in vitro screening assays of TTR ligands acting as amyloidogenesis inhibitors or acting as molecular chaperones to enhance the TTR:Aβ interaction. Preparative yields were up to 660 mg of homogenous protein per L of culture in fed-batch bioreactor. The recombinant wt protein is mainly unmodified at Cys10, the single cysteine in the protein sequence, whereas the highly amyloidogenic Y78F variant renders mainly the S-glutathionated form, which has essentially the same amyloidogenic behavior than the reduced protein with free Cys10. The TTR production protocol has shown inter-batch reproducibility of expression and protein quality for in vitro screening assays.

Characteristics of the brown hagfish Paramyxine atami transthyretin: Metal ion-dependent thyroid hormone binding

Transthyretin (TTR) is a vertebrate-specific protein involved in thyroid hormone distribution in plasma, and its gene is thought to have emerged by gene duplication from the gene for the ancient TTR-related protein, 5-hydroxyisourate hydrolase, at some early stage of chordate evolution. We investigated the molecular and hormone-binding properties of the brown hagfish Paramyxine atami TTR. The amino acid sequence deduced from the cloned hagfish TTR cDNA shared 33-50% identities with those of other vertebrate TTRs but less than 24% identities with those of vertebrate and deuterostome invertebrate 5-hydroxyisourate hydrolases. Hagfish TTR, as well as lamprey and little skate TTRs, had an N-terminal histidine-rich segment, allowing purification by metal-affinity chromatography. The affinity of hagfish TTR for 3,3',5-triiodo-L-thyronine (T3) was 190 times higher than that for L-thyroxine, with a dissociation constant of 1.5-3.9nM at 4°C. The high-affinity binding sites were strongly sensitive to metal ions. Zn²⁺ and Cu²⁺ decreased the dissociation constant to one-order of magnitude, whereas a chelator, o-phenanthroline, increased it four times. The number of metal ions (mainly Zn²⁺ and Cu²⁺) was approximately 12/TTR (mol/mol). TTR was also a major T3-binding protein in adult hagfish sera and its serum concentration was approximately 8μM. These results suggest that metal ions and the acquisition of N-terminal histidine-rich segment may cooperatively contribute to the evolution toward an ancient TTR with high T3 binding activity from either 5-hydroxyisourate hydrolase after gene duplication.

[Identification of transthyretin posttranslational modifications 1n human blood using mass-spectrometric methods]

Transthyretin, one of the major plasma proteins, has a number of posttranslational modifications and mutations, some of which are associated with the development of severe diseases, for instance, familial amyloid neuropathy and Alzheimer's disease. In order to investigate the role of modified forms in the development of these diseases a complex analytical platform, based on two mass-spectrometric approaches (bottom-up and op-down) has been developed. The high efficiency of this method was shown using 10 plasma samples obtained from patients with Alzheimer's disease and healthy individuals.

Characterization and stability of transthyretin isoforms in cerebrospinal fluid examined by immunoprecipitation and high-resolution mass spectrometry of intact protein

Post-translational modifications (PTMs) contribute significantly to the complexity of proteins. PTMs may vary in certain patterns according to diseases and microenviroments making them potential markers for pathological processes. Human transthyretin (TTR) is a transporter of thyroxine and retinol in blood and cerebrospinal fluid (CSF). A single free cysteine thiol group in TTR possesses the ability to form mixed disulfides potentially related to diseases such as TTR amyloidosis and Alzheimer's disease (AD). Additionally, TTR-Cys10 S-thiolations might mirror the oxidative stress and redox balance of CSF. Here we describe a quick and gentle method for immunoprecipitating (IP) TTR from CSF with minimal introduction of sample-handling artifacts. A high-resolution mass spectrometer (LTQ-Orbitrap XL) was used in a simple setup with direct infusion that generates data suitable for confident assignment of TTR isoforms and validation of the protocol. Moreover, we demonstrate how simple storage of CSF at 4°C induces major oxidative modifications of TTR. Using the optimized method, we show data from a limited number of mild cognitive impairment (MCI) and AD patients. The protocol controls and minimizes the introduction of sample-handling artifacts during purification of TTR isoforms for high-resolution MS analysis.

New genetic polymorphism recognized in the prealbumin region of chicken egg yolk

Two-dimensional electrophoretic analysis of water-soluble proteins of chicken egg yolk was done by a first-dimension separation in agarose gel (pH 8.6) followed by a second-dimension separation in horizontal polyacrylamide gel (pH 9.0). Genetic polymorphism of a protein, tentatively designated as Pr M prealbumin, was observed. The analysis of family data suggests that the Pr M prealbumin is controlled by two alleles, Pr M+ and Pr M-, at a single autosomal locus. The Pr M+ allele appears to be dominant to the Pr M- allele.

Transthyretin mass determination for detection of transthyretin familial amyloid

The concentration range of plasma proteins exceeds the dynamic range of any single analytical method. It has been estimated that the concentration range of serum proteins exceeds ten orders of magnitude (1). Because of this, prior immunoselection of even abundant proteins facilitates the relative nonquantitative observations required to show structural abnormality in primary or in posttranslational structure. Determination of atypical proteins by mass measurement has been reported for genetic defects in glycosylation (2, 3) and for monitoring for transthyretin (TTR) defects (4). Here we describe a rapid method of purification and electrospray introduction of TTR into a mass spectrometer to detect mass changes due to amino acid substitutions. The method currently forms the basis for a clinical assay to ascertain TTR mutations resulting in amyloidosis.

Heating of proteins as a means of improving crystallization: a successful case study on a highly amyloidogenic triple mutant of human transthyretin

The use of high temperatures in the purification procedures of heat-stable proteins is a well established technique. Recently, rapid pre-heat treatment of protein samples prior to crystallization trials was described as a final polishing step to improve the diffraction properties of crystals [Pusey et al. (2005), Prog. Biophys. Mol. Biol. 88, 359-386]. The present study demonstrates that extended high-temperature incubation (328 K for 48 h) of the highly amyloidogenic transthyretin mutant TTR G53S/E54D/L55S successfully removes heterogeneities and allows the reproducible growth of well diffracting crystals. Heat treatment might be applied as an optimization method to other cases in which the protein/biomolecule fails to form diffracting crystals.

Identification of potential markers for the detection of pancreatic cancer through comparative serum protein expression profiling

OBJECTIVE

Early detection is the only promising approach to significantly improve the survival of patients with pancreatic cancer (PCa). Noninvasive tools for the diagnosis, prognosis, and monitoring of this disease are of urgent need. The purpose of this study was to identify and validate new biomarkers in PCa patient serum samples.

METHODS

Surface-enhanced laser desorption/ionization time-of-flight mass spectrometry has been applied to analyze serum protein alterations associated with PCa and to identify sets of potential biomarkers indicative for this disease. A cohort of 96 serum samples from patients undergoing PCa surgery was compared with sera from 96 healthy volunteers as controls. The sera were fractionated by anion exchange chromatography, and 3 of 6 fractions were analyzed onto 2 different chromatographic arrays.

RESULTS

Data analysis revealed 24 differentially expressed protein peaks (P < 0.001), of which 21 were downregulated in the PCa samples. The best single marker can predict 92% of the controls and 89% of the cancer samples correctly. In addition, multivariate pattern analysis was performed. The best pattern model using a set of 3 markers was obtained using fraction 6 on immobilized metal affinity capture, loaded with Cu-Cu arrays. With this pattern model, a sensitivity of 100% and a specificity of 98% for the training data set and a sensitivity of 83% and specificity of 77% for the test data set were achieved with the PCa group set as true positive. Several of protein peaks, including the best single marker at 17.27 kd and other proteins from the pattern models, were purified and identified by peptide mapping and postsource decay-matrix-assisted laser desorption ionization-time-of-flight mass spectrometry. Apolipoprotein A-II, transthyretin, and apolipoprotein A-I were identified as markers, and these identified proteins were decreased at least 2-fold in PCa serum when compared with the control group.

CONCLUSIONS

PCa is associated with a specific decrease of distinct serum proteins, which allows a reliable differentiation between pancreatic cancer and healthy controls.

Detailed structural analysis of amyloidogenic wild-type transthyretin using a novel purification strategy and mass spectrometry

Wild-type transthyretin (TTR), normally a soluble plasma-circulating protein, can be amyloidogenic, i.e., form tissue-deposited fibrillar material in the extracellular matrix of various organs throughout the body. Senile systemic amyloidosis (SSA) is one such pathology and features TTR-containing amyloid deposits that are found primarily in the heart. The cause for this transition from soluble to insoluble protein in SSA is yet to be determined as specific structural features that might favor TTR fibrillogenesis have not yet been identified. The precise characterization of ex vivo fibril deposits might provide insight, but structural analyses of TTR from amyloid deposits have been hindered thus far by the lack of purification strategies that overcome the insolubility of the tissue-derived protein without degrading it. Consequently, the true biochemical nature of deposited TTR remains in question. In this study, we provide detailed analyses of both the soluble (serum) and deposited (tissue) forms of TTR from cases of SSA. In the serum, a distribution of mixed disulfides, specifically S-sulfonated and S-cysteinylated forms of TTR, as well as the unmodified protein were identified. The relative levels of the three TTR species in the SSA group were comparable to amounts present in sera from age-matched control groups. For characterization of the amyloid deposited TTR, we investigated cardiac tissue samples obtained from three separate cases of SSA. We report a novel chromatographic purification strategy performed under nonreducing conditions (to maintain cysteine disulfide status) and the use of this procedure in conjunction with detailed mass spectrometric analysis of TTR from the amyloid deposits. A series of C-terminal TTR fragments with N-termini ranging from amino acids 46 to 55 were identified. We also determined that the deposits in all samples contained Cys10 disulfide-linkedhomodimers composed of full-length TTR monomers. This last finding suggests an important role for Cys10 conjugation in the transition from soluble TTR to the pathological amyloid fibril.

Expression, purification, and in vitro cysteine-10 modification of native sequence recombinant human transthyretin

Transthyretin (TTR) is a serum protein that is also a prominent component of deposits in two different types of systemic amyloid disease, senile systemic and familial TTR amyloidoses. Studies of recombinant TTR (rTTR) have provided many insights into the relationship between protein structure and amyloidogenicity. Yet, there is no existing recombinant system that results in high yield production of a protein that is identical in primary structure to human TTR. To date, most published studies have generated rTTR using the human gene sequence, which is poorly expressed in Escherichia coli. In addition, the gene sequence has been flanked by a 3' AUG start codon to initiate translation, resulting in the expression of a protein containing an N-terminal methionine residue not present in the human protein. We present an improved technique which can be used to generate large quantities of human native sequence TTR. Our recombinant system utilizes a gene containing codons altered for efficient expression in E. coli and an N-terminal polyhistidine tag for simplified purification. Optimization of this system was accomplished by generating a modified polyhistidine tag that was efficiently removed by dipeptidyl aminopeptidase I (DAPase). This is the first report detailing an effective and useful method for producing rTTR containing an amino acid sequence identical to human TTR. Furthermore, we describe the thiol modification of the recombinant protein to achieve exact replication of the several prominent post-translationally modified forms of TTR that have been identified in human serum.

Dysregulation of retinoid transporters expression in body fluids of schizophrenia patients

This study aims to find the biomarkers or associated proteins in body fluids of schizophrenia patients so that we can further understand the etiology of schizophrenia. We applied proteomic technologies combining two-dimensional electrophoresis with Coomassie blue staining and mass spectrometry and identified a procedure for the clinical screening of disease-influenced body fluid proteins in two sets of samples, plasma from 19 schizophrenia patients and cerebrospinal fluid (CSF) from 35 drug-treated schizophrenic patients and 36 healthy controls. The expression of transthyretin (TTR) tetramer increased significantly in plasma of schizophrenic patients after a valid 2 months in-hospital antipsychotic treatment. Conversely, the expression of the TTR tetramer and apolipoprotein E (ApoE) was down-regulated by up to 1.68 and 3.62 times, respectively, in the CSF of schizophrenia patients compared to that of normal controls, which has not been reported previously. Considering that the TTR tetramer and ApoE are both retinoid transporters, retinoid dysfunction might be involved in the pathology of schizophrenia.

Characterization of transthyretin in the Pacific bluefin tuna, Thunnus orientalis

A cDNA encoding transthyretin was cloned from the Pacific bluefin tuna (Thunnus orientalis). This cDNA contains a complete open reading frame encoding 151 amino acid residues. The deduced amino acid sequence is 81% and 55% identical to the gilthead seabream and common carp forms, respectively, and 33-39% to mammalian, reptilian, and amphibian forms. A 1.0-kb transcript was found in the the liver and ovary; the liver is the main source of this protein. Analysis of triiodo-L-thyronine (T(3)) and L-thyroxine (T(4)) binding demonstrated that both T(3) and T(4) bind to bluefin transthyretin. The binding activity of T(3) for bluefin transthyretin is higher than that of T(4). These results indicate that bluefin transthyretin acts as a transporter of thyroid hormones (THs) in the plasma, and plays an important role in the function of THs in target cells.

Use of a 13C tracer to investigate lutein as a ligand for plasma transthyretin in humans

The selective accumulation of lutein in the macula of the human retina is likely to be mediated by specific transport and/or binding proteins. Our objective was to determine whether transthyretin (TTR) is a plasma transport protein for lutein. We used a biosynthetic 13C-lutein tracer and GC-combustion interfaced-isotope ratio MS to gain the requisite sensitivity to detect the minute amounts of lutein expected as a physiological ligand for TTR. Subjects (n = 4) each ingested 1 mg of 13C-lutein daily for 3 d and donated blood 24 h after the final dose. For three subjects, the plasma TTR-retinol-binding protein (RBP) complex was partially purified by anion-exchange (diethylaminoethyl, DEAE) chromatography and then dissociated by hydrophobic-interaction chromatography to yield the TTR component. For subject 4, the initial DEAE purification step was omitted and total plasma TTR (RBP-bound and free) was isolated by hydrophobic-interaction chromatography. In each case, the crude TTR fractions were then purified to homogeneity by RBP-Sepharose affinity chromatography. Pure TTR was extracted with chloroform, and unlabeled lutein was added to the extract as a carrier. The mean 13C/12C ratio (expressed in delta notation, delta13C) of the lutein fraction isolated from the plasma TTR extracts of the four subjects was -30.53 +/- 3.29 per thousand. The delta13C value of the unlabeled lutein carrier was -30.97 +/- 0.27per thousand. Thus, no 13C enrichment was detected in association with TTR. We conclude that lutein is not associated with TTR in human plasma after being ingested in physiological amounts.

The effect of iodide and chloride on transthyretin structure and stability

Transthyretin amyloid formation occurs through a process of tetramer destabilization and partial unfolding. Small molecules, including the natural ligand thyroxine, stabilize the tetrameric form of the protein, and serve as inhibitors of amyloid formation. Crucial for TTR's ligand-binding properties are its three halogen-binding sites situated at the hormone-binding channel. In this study, we have performed a structural characterization of the binding of two halides, iodide and chloride, to TTR. Chlorides are known to shield charge repulsions at the tetrameric interface of TTR, which improve tetramer stability of the protein. Our study shows that iodides, like chlorides, provide tetramer stabilization in a concentration-dependent manner and at concentrations approximately 15-fold below that of chlorides. To elucidate binding sites of the halides, we took advantage of the anomalous scattering of iodide and used the single-wavelength anomalous dispersion (SAD) method to solve the iodide-bound TTR structure at 1.8 A resolution. The structure of chloride-bound TTR was determined at 1.9 A resolution using difference Fourier techniques. The refined structures showed iodides and chlorides bound at two of the three halogen-binding sites located at the hydrophobic channel. These sites therefore also function as halide-binding sites.

Purification of transthyretin and transthyretin fragments from amyloid-rich human tissues

Transthyretin is the major amyloid fibril protein in many forms of familial systemic amyloidosis where a missense mutation creates an amyloidogenic protein, and in senile systemic amyloidosis in which wild-type transthyretin aggregates into amyloid fibrils. The amyloid deposits may consist of full-length transthyretin but is very often, in senile systemic amyloidosis always, a mixture of full-length transthyretin and C-terminal transthyretin fragments. The amyloid fibril protein mixture can be purified by extraction of fibrils followed by sequential gel filtration after solubilization in a solution of guanidine hydrochloride. Since the C-terminal transthyretin fragments lack cysteine residues, a method to separate full-length transthyretin from fragments by covalent chromatography has been developed.

Kinetic Stabilization of the Native State by Protein Engineering: Implications for Inhibition of Transthyretin Amyloidogenesis

The amyloidogenic homotetrameric protein transthyretin (TTR) must undergo rate-limiting dissociation to partially denatured monomers in order to aggregate. TTR contains two distinct quaternary interfaces, one of which defines the binding sites for thyroxine and small-molecule amyloidogenesis inhibitors. Kinetic stabilization of the tetramer can be accomplished either by the binding of amyloidogenesis inhibitors selectively to the native state over the dissociative transition state or by the introduction of trans-suppressor subunits (T119M) into heterotetramers to destabilize the dissociative transition state. In each case, increasing the dissociation activation barrier prevents tetramer dissociation. Herein, we demonstrate that tethering two subunits whose quaternary interface defines the thyroxine binding site also dramatically increases the barrier for tetramer dissociation, apparently by destabilization of the dissociative transition state. The tethered construct (TTR-L-TTR)2 is structurally and functionally equivalent to wild-type TTR. Urea is unable to denature (TTR-L-TTR)2, yet it is able to maintain the denatured state once denaturation is achieved by GdnHCl treatment, suggesting that (TTR-L-TTR)2 is kinetically rather than thermodynamically stabilized, consistent with the identical wild-type TTR and (TTR-L-TTR)2 GdnHCl denaturation curves. Studies focused on a construct containing a single TTR-L-TTR chain and two normal monomer subunits establish that alteration of only one quaternary structural interface is sufficient to impose kinetic stabilization on the entire quaternary structure.

A new method for purification of human plasma retinol-binding protein and transthyretin

Retinol is transported in the blood bound to a specific carrier protein called retinol-binding protein (RBP), which in turn binds to another protein, transthyretin (TTR), a homotetrameric, thyroid-hormone-transporting protein. Binding of TTR increases the apparent molecular mass of RBP and thereby prevents glomerular filtration of RBP. Owing to their rapid turnover rates, plasma concentrations of these proteins are sensitive indicators and valuable diagnostic markers of vitamin A nutrition, protein energy malnutrition, infection and renal-tubule function. Previously RBP and TTR were purified by using different procedures, either from plasma or from pathological urine of humans. In general the procedure for purification of RBP and TTR is laborious, and extensive sample recycling is necessary for purification in appreciable amounts. In the present study, we have purified RBP using a simple method, which involves (NH(4))(2)SO(4) fractionation followed by sequential gel filtration under native conditions and 6 M urea. TTR, which was eluted in 60 kDa fractions during urea/Sephadex G-100 chromatography, was further purified to homogeneity using a combination of two dye-affinity chromatographic steps on Reactive Yellow and Cibacron Blue coupled to agarose columns. SDS/PAGE and immunoblotting, apart from typical UV absorption and fluorescent properties of RBP, were used for characterizing the purified RBP and TTR. Furthermore, the purified RBP and TTR were found to be functional from mutual binding monitored by fluorescence quenching.

Expression of a synthetic gene encoding human transthyretin in Escherichia coli

Transthyretin is an amyloidogenic protein that causes human amyloid polyneuropathy and senile systemic amyloidosis as a result of the deposition of normal and/or mutant transthyretin in the form of amyloid fibrils. A high-expression plasmid of human transthyretin was constructed in order to facilitate the study of amyloid fibril formation of this protein. The transthyretin gene was constructed by an assembly of eight chemically synthesized oligonucleotides and amplified by polymerase chain reaction, and the amplified gene was inserted into an Escherichia coli expression vector. The expression plasmid was transformed into M15 cells and the gene product was expressed as a polyhistidine-tagged fusion protein. Purified recombinant transthyretin was obtained by one-step nickel chelation affinity chromatography and the production level of the protein was 130mg per 1L of culture. Furthermore, the expressed protein showed the same characteristics in terms of tetramer formation at neutral pH and amyloid formation at acidic pH as did the authentic human transthyretin. This system will enable biophysical and structural studies of this protein to be advanced.

Polyacrylamide gel electrophoresis followed by sodium dodecyl sulfate gradient polyacrylamide gel electrophoresis for the study of the dimer to monomer transition of human transthyretin

Familial amyloidotic polyneuropathy (FAP) is caused by mutations which destabilize transthyretin (TTR) and facilitate the aggregation into extracellular amyloid fibrils preferentially in peripheral nerve and heart tissues. Therapeutic and preventive trials for FAP at the plasma TTR level require a careful study of the destabilization of TTR under variable conditions. We have developed a simple double one-dimensional (D1-D) electrophoretic procedure with polyacrylamide gel electrophoresis (PAGE) followed by sodium dodecylsulfate (SDS) gradient PAGE to study the dimer to monomer transition. TTR is first isolated by PAGE from other plasma proteins. The gel strip containing the TTR fraction is incubated in 2% SDS under varying conditions of temperature, buffer composition, pH, and additives like urea and/or a sulfhydryl-reactive agent, followed by SDS-gradient PAGE for the separation of TTR dimers and monomers. We demonstrate that an unidirectional dimer to monomer transition of normal TTR is achieved at 70-80 degrees C in neutral to mild alkaline buffers or at 37 degrees C and slightly acidic pH (6-7). Addition of urea favors the transition into monomers. Amyloidogenic mutations like amyloidogenic TTR (ATTR)-V30M or ATTR-I107V favor the transition into monomers in buffer systems close to the physiological pH of human plasma. We conclude that this finding has to be considered by any hypothesis on ATTR-derived amyloidogenesis.

Serum biomarkers of hepatitis B virus infected liver inflammation: a proteomic study

Hepatitis B virus (HBV), a serious infectious and widespread human pathogen, represents a major health problem worldwide. Chronic HBV infection has a very high risk of evolving into hepatocellular carcinoma. Although considerable progress was made during the recent past, the pathogenesis of HBV infection is still elusive and a definite diagnosis of HBV infected liver information still relies on biopsy histological test. In this report, we used proteomics technology to globally examine HBV infected serum samples aiming at searching for disease-associated proteins that can be used as serological biomarkers for diagnosis and/or target proteins for pathogenetic study. By comparing with normal and HBV negative serum samples, we found that at least seven proteins were significantly changed in HBV infected sera. These greatly altered proteins were identified to be haptoglobin beta and alpha2 chain, apolipoprotein A-I and A-IV, alpha1-antitrypsin, transthyretin and DNA topoisomerase IIbeta. The alteration of these proteins is displayed not only in quantity but also in patterns (or specificity), which can be correlated with necroinflammatory scores. In particular, apolipoprotein A-I presents heterogeneous change in expression level with different isoforms and alpha1-antitrypsin produces evidently different fragments implying diverse cleavage pathways. These unique phenomena appear specific to HBV infection. A combination simultaneously considering the quantities and isoforms of these proteins could be a useful serum biomarker (or index) for HBV diagnosis and therapy.

Amyloid formation in rat transthyretin: effect of oxidative stress

BACKGROUND

Transgenic mice carrying a human mutant transthyretin (TTR) gene are too small for in vivo experiments. It is necessary to have rat TTR protein and its antibody to overcome this problem.

METHODS

Posttranslational modification of purified TTR was analyzed by means of matrix-assisted laser desorption ionization/time-of-flight mass spectrometry (MALDI/TOF-MS). Production of amyloid fibrils in vitro was confirmed by thioflavin T test and electron microscopy. Amyloidogenicity of rat TTR from rats with or without challenging paraquat was compared in vitro by thioflavin T test.

RESULTS

MALDI/TOF-MS for rat TTR revealed three major modified forms-sulfate-conjugated, Cys-conjugated and glutathione-conjugated-in addition to the unconjugated (free) form of TTR. Although rat TTR in buffer of pH 7.0 could not make amyloid fibrils, rat TTR at pH 2.0-3.5 significantly formed amyloid fibrils, as confirmed by the thioflavin T test and electron microscopy. TTR purified from rats administered 4 mg/kg of paraquat formed much more amyloid fibrils than that from normal rats at pH 2.0-3.5 and significant amyloid fibrils were confirmed even at pH 7.0.

CONCLUSIONS

Rat TTR may be a valuable experimental tool for examination of the amyloidogenicity of senile systemic amyloidosis (SSA) as well as familial amyloidotic polyneuropathy (FAP) both in vitro and in vivo.

Comparison of preparative and analytical two-dimensional electrophoresis for isolation and matrix-assisted laser desorption/ionization-time-of-flight mass spectrometric analysis of transthyretin in cerebrospinal fluid

The variety of posttranslational modifications and the relative abundance of transthyretin (TTR) in cerebrospinal fluid (CSF) make TTR a suitable model molecule when comparing the performance of different combinations of methods for characterization of CSF proteins. We have compared three different electrophoretic methods: conventional two-dimensional gel electrophoresis (2-DE), liquid-phase isoelectric focusing (IEF) as a prefractionation step in combination with analytical 2-DE, and preparative 2-DE for isolation and mass spectrometric analysis of TTR in CSF. Using liquid-phase IEF in combination with 2-DE compared with conventional 2-DE improved the sequence coverage of TTR. Only the mass spectrum from the preparative 2-DE fraction contained a tryptic peptide from the first nine amino acids, thereby yielding 100% sequence coverage. Our results show that the use of a prefractionation step before 2-DE or the use of preparative 2-DE increases the sequence coverage and provide low abundant proteins in complex biological systems in sufficient quantities for protein characterization with mass spectrometry.

Protein standardization I: Protein purification procedure for the purification of human prealbumin, orosomucoid and transferrin as primary protein preparations

A procedure for the purification of human prealbumin, orosomucoid and transferrin as primary protein preparations has been developed. The procedure describes in detail the chemicals, the fractionation equipment and the purification of the three proteins from the same starting material (a 90-donor plasma pool). The fractionation steps involve methods like salting out, various anion and cation exchange chromatographies, preparative electrophoresis, and finally, size chromatography. Only mild and highly reproducible fractionation methods are used in order to obtain high recoveries. All of these provide the best guarantee that no serious subfractionation has taken place. At the same time, high recoveries are a necessity for the pure protein to be representative of the same protein in vivo. The following recoveries were obtained: prealbumin 55%, orosomucoid 70% and transferrin 85%. The pure proteins are produced as liquid calibrators (primary protein preparations) dissolved in one electrolyte (0.1 mol/l KCl) and stored in sealed glass ampoules at -80 degrees C. These three pure proteins were used as primary reference preparations in the certification of the international reference preparation CRM 470.

Codeposition of apolipoprotein A-IV and transthyretin in senile systemic (ATTR) amyloidosis

Protein material was extracted from amyloid-rich sections of formalin-fixed and paraffin-embedded heart tissue from an individual with senile systemic amyloidosis, known to contain wild-type transthyretin as major amyloid fibril protein. Amino acid sequence analysis of tryptic peptides of this material revealed in addition to transthyretin sequences, also amino acid sequence corresponding to an N-terminal fragment of apolipoprotein A-IV. In immunohistochemistry, an antiserum to a synthetic apolipoprotein A-IV peptide labeled amyloid specifically. This peptide formed spontaneously amyloid-like fibrils in vitro and enhanced fibril formation from wild-type transthyretin. We conclude that several apolipoproteins, including apolipoprotein A-IV, may be important minor amyloid constituents, promoting fibril formation.

Enhancement of AA-amyloid formation in mice by transthyretin amyloid fragments and polyethylene glycol

The mechanism behind amyloid formation is unknown in all types of amyloidosis. Several substances can enhance amyloid formation in animal experiments. To induce secondary systemic amyloid (AA-type amyloid) formation, we injected silver nitrate into mice together with either amyloid fibrils obtained from patients with familial polyneuropathy (FAP) type I or polyethylene glycol (PEG). Mice injected with silver nitrate only served as controls. Amyloid deposits were detectable at day 3 in animals injected with amyloid fibrils and in those injected with PEG, whereas in control mice, deposits were not noted before day 12. Our results indicate that amyloid fibrils from FAP patients and even a non-sulfate containing polysaccharide (PEG) have the potential to act as amyloid-enhancing factors.

A new nonamyloid transthyretin variant, G101S, detected by electrospray ionization/mass spectrometry. Mutations in brief no. 201. Online

Familial amyloidotic polyneuropathy is caused by transthyretin (TTR) variants. The identification of new variants with and without amyloidosis may help to clarify the mechanism of amyloid fibril formation. We detected several variant TTRs from patients with and without symptoms of amyloidosis using mass spectrometry (MS). TTR was isolated by mixing test serum with anti-transthyretin antiserum, and the generated immunoprecipitate was analyzed by high performanced liquid chromatography/electrospray ionization (HPLC/ESI) MS. Variant TTRs showed extra peaks in addition to normal TTR peaks. A variant found in nonamyloid group was sequenced by HPLC/ESI tandem MS using peptides obtained by protelytic digestion of TTR and by DNA analysis. The structure was new, [G101S], and was found in a 74 years old Japanese male. This mutation results from substitution in a CpG hot spot. The substitution in the surface loop, 98-102, between F and G b-strands may not cause amyloid formation.

A factor that prevents EDTA-induced cell-growth inhibition: purification of transthyretin from chick embryo brain

We previously reported the inhibition of cell-growth in Neuro-2A cells, mouse neuroblastoma, by Zn2+ chelation with EDTA. This paper describes the purification of a factor that prevents EDTA-induced cell-growth inhibition from chick embryo brain. The purified factor has a molecular mass of 16 kDa on SDS-polyacrylamide gel electrophoresis under reducing conditions. This factor prevents the cell-growth inhibition in a dose-dependent manner and also binds thyroxine. Analysis of the N-terminal amino acid sequence revealed that 40 residues coincide with the sequence of chicken liver transthyretin.

Crystallization and preliminary X-ray data for the human transthyretin-retinol-binding protein (RBP) complex bound to an anti-RBP Fab

A macromolecular complex of human transthyretin, human retinol-binding protein and an anti-retinol-binding-protein Fab was crystallized by vapour diffusion in sitting drops. Diffraction from these crystals at cryogenic temperatures was consistent with the space group C222, with cell parameters a = 159.34, b = 222.40 and c = 121.27 A. Crystals diffracted to a resolution limit of 3.36 A using synchrotron radiation. Based on a 2:2:1 stoichiometry for the Fab-retinol-binding-protein-transthyretin complex and the presence of one such complex per asymmetric unit, a reasonable Vm coefficient of 2.74 A3 Da-1 could be estimated.

A selective transthyretin-adsorption column for the treatment of patients with familial amyloid polyneuropathy

A transthyretin (TTR)-adsorption column has been developed for the removal of variant TTR from the plasma of patients with familial amyloid polyneuropathy (FAP). The adsorbent is an ion-exchange resin made of porous beads of polyvinyl alcohol gel covalently bound with dimethylaminoethanol. This column was used for three patients with type I FAP. It reduced the concentrations of both normal and variant TTR in the plasma to about half of their pre-adsorption levels. Except for thyroxine, retinol-binding protein and IgM, other proteins in serum were not significantly decreased and there were no adverse effects in long term clinical usage of this TTR-adsorption column. In this trial, we did not obtain concrete evidence that TTR-adsorption therapy can stop or delay the progression of the disease in a FAP patient. However, if we are able to apply this technique more frequently and effectively, TTR-adsorption therapy using our column might be useful for the treatment of FAP patients.

Purification of transthyretin by high performance affinity chromatography from human plasma

The partial purification of human transthyretin (TTR) by high performance affinity chromatography with the help of other separation techniques is described in the present paper. A new affinity medium was prepared with a monosized (ca. 10 microns particle size) macroporous resin as the support and thyroxine (T4) as the ligand. The purification of TTR was carried out in a few simple steps involving serum precipitation, anion exchange, Thyroxine affinity chromatography and gel filtration. The overall yield was 29% and the refined TTR contained less than 2% impurities as analyzed by RP-HPLC. When TTR was administrated to the culture medium DMEM of liver tumor strain SMMC-7721, a true inhibition of cell growth (ca. 50%) was observed as an actual decrease in cell number over time.

Lutein associated with a transthyretin indicates carotenoid derivation and novel multiplicity of transthyretin ligands

Transthyretins isolated from different species bind hydrophobic compounds and are often obtained in a yellow form. Such a transthyretin from chicken serum was purified by chromatography using Sepharose-coupled human retinol-binding protein. The yellow chromophore was extracted with methanol and purified by reverse phase HPLC followed by normal-phase chromatography on a nitrile column. Ultraviolet-visible absorbance and mass spectrometry identified the yellow compound as lutein, i.e. xanthophyll, (all-trans)-beta, epsilon-carotene-3,3'-diol, estimated to constitute 10-30% of associated colourless compounds. These components are different from the yellow component isolated from human transthyretin and establish that carotenoid-derived pigments can be associated with transthyretins.

Transport of serum transthyretin into chicken oocytes. A receptor-mediated mechanism

Transthyretin (TTR) is involved in the transport of thyroid hormones and, due to its interaction with serum retinol-binding protein, also of vitamin A. The importance of both ligands in vertebrate embryonic development has prompted us to investigate the molecular details of TTR transport function in a powerful germ cell system, the rapidly growing chicken oocytes. Yolk TTR is derived from the circulatory system, since biotinylated TTR was recovered by immunoaffinity chromatography of yolk obtained from a hen previously infused with in vitro biotinylated chicken serum proteins. In concordance with the intraoocytic localization in an endosomal compartment, ligand blotting and chemical cross-linking experiments revealed the presence of a approximately 115-kDa TTR-binding oocyte membrane protein. This putative TTR receptor was not detected in chicken ovarian granulosa cells or embryonic fibroblasts and was different from the previously described oocyte-specific receptor for two estrogen-induced chicken serum lipoproteins, vitellogenin and very low density lipoprotein (Barber, D. L., Sanders, E. J., Aebersold, R., and Schneider, W. J. (1991) J. Biol. Chem. 266, 18761-18770). Furthermore, in contrast to the serum levels of the yolk precursor lipoproteins, those of TTR were not significantly changed by estrogen; thus, TTR represents a newly defined, estrogen-independent class of yolk precursor proteins. These data strongly suggest that oocytic TTR is derived from the circulation, where it is a constitutive component, and deposited into yolk as a result of endocytosis mediated by a specific receptor.

Porcine VEG proteins and tear prealbumins

Small soluble proteins, belonging to the lipocalin family are secreted in large amounts by tongue von Ebner's glands and lachrymal glands. In humans, the lingual protein, called VEG, and the lachrymal protein, called tear prealbumin, have shown identical cDNA sequences. In the pig, we have purified homodimeric proteins with subunits of 17 kDa, both from von Ebner's glands and from lachrymal glands. In both cases, the proteins can be resolved into two isoforms on a chromatofocusing column. Partial aminoacid sequences and full cDNA sequences have been obtained for the more abundant forms purified from both tissues. The two proteins appear to be identical, as in humans. The reason why the same protein is expressed in different tissues, as well as its physiological function, still remain to be clarified.

Purification and characterization of amyloid-related transthyretin associated with familial amyloidotic cardiomyopathy

Analysis of amyloid fibril material associated with familial amyloidotic cardiomyopathy revealed that it contains a mixture of transthyretin-related polypeptides. The major protein band in SDS/polyacrylamide gel corresponding to a molecular mass of 14.5 kDa, consists of transthyretin fragments starting at positions 46, 49 and 59, the latter not previously identified, and one blocked fragment derived from the N-terminal part of transthyretin. In reverse-phase HPLC, the major fragment recovered was that starting at Thr49, indicating a trypsin-like cleavage (Lys at position 48). Two minor bands, corresponding to 17 kDa and 35 kDa, contained proteins with blocked N-termini, and migrated as monomeric and dimeric transthyretin, respectively. A 13-kDa protein band was found to contain transthyretin with a ragged N-terminus, mainly starting at positions 2 and 5. Three more bands, corresponding to 10, 25 and 29 kDa, consist of transthyretin molecules with blocked N-termini and most likely of aggregates of truncated molecules. A point mutation of amyloid transthyretin was identified at position 111 (Met instead of Leu in normal serum transthyretin) which confirms the mutation found for Danish siblings with familial amyloidotic cardiomyopathy. However, the presence of a non-variant amyloid transthyretin was also observed, indicating that the Danish kindred is heterozygous with respect to this point mutation. Isoelectric focusing of the amyloid fibril material resolved multiple protein bands ranging over pH 4.5-6.5, confirming heterogeneities. Methanol extraction of the cardiac amyloid fibril material prior to the purification steps reveals a methanol-soluble substance amounting to about 10% (by mass dry material) of the amyloid fibril material. A yellow substance in this fraction shows absorbance maxima (270, 280 and 430 nm) similar to those observed for transthyretin in normal serum. Gas chromatography/mass spectrometry of the methanol extract revealed the presence of saturated fatty acids (C14:0, C16:0 and C18:0 in the corresponding ratio 2:8:5) and polyunsaturated fatty acids (C16:1, C18:1, C18:2 and C20:4 in the corresponding ratio of 1:2:1:1) as further constituents of the amyloid fibril material.

Structural organization of the gene encoding the human lipocalin tear prealbumin and synthesis of the recombinant protein in Escherichia coli

The genomic DNA fragment encoding the human lipocalin tear prealbumin (LCN1), a new member of the superfamily of hydrophobic molecule transporters, has been isolated and sequenced. The entire gene is approximately 6.2 kb in size and contains six protein-coding exons and a 3'-nontranslated exon. All exon/intron splice junctions exactly follow the GT/AG rule. The structure of the LCN1 gene is highly similar, in terms of numbers and sizes of exons and in intron phasing, to that of the genes encoding ovine beta-lactoglobulin, human placental protein P14, rat alpha 2-urinary globulin, rat prostaglandin D synthase and human alpha 1-microglobulin, thus supporting the close evolutionary relationship of these genes. The 5'-noncoding region of LCN1 contains, besides a TATA and CAAT box, several motifs that resemble regulatory elements of other eukaryotic genes, including potential metal-responsive elements (MRE) and a cAMP-responsive element (CRE). As a basis for further investigations concerning the structure-function relationship and to generate a source of recombinant protein for X-ray crystallography studies, LCN1 was produced in Escherichia coli as a fusion with maltose-binding protein.

Intermolecular disulfide linkages are not required for transthyretin amyloid fibril formation in vitro

The role of intermolecular disulfide linkages in transthyretin (TTR) amyloid fibril formation was investigated by comparing wild type TTR to Cys-10-Ala TTR which is incapable of disulfide formation. The Cys-10-Ala variant exhibits quaternary structural stability equal to the wild type protein under acidic denaturing conditions. Both Cys-10-Ala and wild type TTR were converted into amyloid fibrils by partial acid denaturation. There was no evidence of intermolecular disulfide formation in the case of wild type amyloid fibrils. These results are inconsistent with a recently proposed model stressing the importance of intermolecular disulfide linkages in TTR amyloid fibril formation, but are consistent with a model relying on noncovalent quaternary contacts made possible through an acid-mediated conformational change.

Transthyretin gene expression in choroid plexus first evolved in reptiles

The presence of transthyretin in mammals and birds, but not amphibia, suggested that transthyretin expression first appeared in stem reptiles. Therefore, transthyretin synthesis was studied in a lizard. Transthyretin synthesis in choroid plexus pieces from Tiliqua rugosa was demonstrated by incorporation of radiactive amino acids. Oligonucleotides corresponding to conserved regions of transthyretin were used as primers in polymerase chain reaction with lizard choroid plexus cDNA. Amplified DNA was used to screen a lizard choroid plexus cDNA library. A full-length transthyretin cDNA clone was isolated and sequenced. A three-dimensional model of lizard transthyretin was obtained by homology modeling. The central channel of transthyretin, containing the thyroxine-binding site, was found to be completely conserved between reptiles and mammals. Transthyretin expression was not detected in lizard liver. These data suggest that transthyretin first evolved in the choroid plexus of the brain. Due to a change in tissue distribution of gene expression, occurring much later during evolution, transthyretin also became a plasma protein, synthesized in the liver.

Transport and uptake of retinol during chicken oocyte growth

Most, if not all, components found in the yolk of a chicken egg are extracted from the plasma compartment during the rapid growth phase of the oocyte. Uptake of the major yolk constituents, very-low-density lipoprotein and vitellogenin, has been shown to be mediated by a specific receptor in the plasma membrane of the oocyte (Barber, D.L., Aebersold, R., Sanders, E.J. and Schneider, W.J. (1991) J. Biol. Chem. 266, 18761-18770). In the current study, we sought biochemical evidence for the uptake into oocytes of a minor but biologically very important component, the vitamin retinol. For transport in serum, retinol is bound to retinol-binding protein (RBP), which in turn forms a complex with transthyretin (TTR). In order to gain insight into the biochemical details of transport of the vitamin, we have identified, purified and characterized RBP, TTR, and RBP-TTR complexes from chicken serum and yolk. The results demonstrate that both serum and yolk contain the tertiary retinol-RBP-TTR complexes as well as free RBP and TTR. Western blots of yolk collected from oocytes at different stages of growth show that both RBP and TTR, but not albumin, are more abundant at early stages relative to total yolk protein. In addition, we find both RBP and TTR in endocytic clathrin-coated vesicles of the oocyte. Our results support the hypothesis that retinol, which must be imported by the oocyte for proper embryonic development, is internalized by the chicken oocyte bound to its serum protein-transport complex.

Cardiac amyloidosis: a review and report of a new transthyretin (prealbumin) variant

Cardiac amyloidosis is caused by amyloid deposits derived from different human plasma proteins. It can lead to cardiac conduction disturbances, restrictive cardiomyopathy, and low output heart failure. The heart is variably involved during the development of systemic amyloidosis and seems to be more frequently affected in immunoglobulin (primary) than in reactive (secondary) amyloidosis. Amyloid is common in the elderly. Isolated atrial amyloid, for which a major subunit is the atrial natriuretic peptide, seems to be three times more frequent than senile cardiac amyloid, which is derived from normal prealbumin (transthyretin). Like polyneuropathy, cardiac amyloidosis is a prominent clinical feature of hereditary amyloidosis, namely of the autosomal dominant transthyretin (TTR) type. All 28 cases of TTR amyloidoses reported so far were heterozygotes for a single nucleotide change in the gene for TTR that resulted in amino acid substitutions in the mature protein. A new TTR genetic variant is reported in a German family where the index patient presented at the age of 63 with anginal pain and arrhythmia. Electrocardiography was suggestive of a pseudoinfarction pattern, and echocardiography and cardiac catheterisation showed signs of hypertrophic nonobstructive cardiomyopathy with increased ventricular filling pressures and a prominent "a" wave. Amyloid of the TTR type was identified by immunohistochemistry in the endomyocardial biopsy specimen. Hybrid isoelectric focusing established heterozygosity by showing normal TTR protein and an electrically neutral TTR variant differing from all known TTR variants so far. The patient died in an accident before investigations were complete. Electrophoretic analysis of the plasma from his first degree relatives (son, daughter, brother, and mother) identified the asymptomatic 22 year old son as an apparently heterozygous carrier of the mutant TTR protein. Comparative tryptic peptide mapping and sequencing showed that isoleucine at position 68 of the amino acid sequence was replaced by leucine.

Circulating proalbumin associated with a second case of antitrypsin Pittsburgh

We report here the conclusive identification of circulating proalbumin of normal N-terminal sequence (Arg Gly Val Phe Arg Arg Asp Ala) in a second child with the alpha 1-antitrypsin Pittsburgh 358 Met-->Arg mutation. As in the first case, the proalbumin made up 3-5% of the total serum albumin. The finding of proalbumin associated with a second de novo mutation at the inhibitory site bait of antitrypsin confirms our earlier hypothesis; that antitrypsin Pittsburgh was acting as a specific intracellular inhibitor of the hepatic proalbumin convertase and that antitrypsin Pittsburgh could be used as a probe to identify the proprotein convertase.

Purification of biologically active human plasma transthyretin by dye-affinity chromatography: studies on dye leakage and possibility of heat treatment for virus inactivation

The application of a purification procedure for the industrial preparation from human plasma of a therapeutic protein may be hindered by several safety concerns. The dye leaching from Remazol Yellow GGL-Sepharose used for the affinity chromatography of human plasma transthyretin was quantitatively studied by a sensitive competitive enzyme immunoassay. The possibility of including a heat treatment step for virus inactivation in the purification process while preserving the biochemical and functional characteristics of the protein is also reported.

A sensitive enzyme immunoassay for the detection of a synthetic affinity ligand, the reactive yellow 13 dye

Dye-affinity chromatography is widely and increasingly used for the isolation of various proteins. In particular, the purification of transthyretin can be efficiently achieved by affinity chromatography on immobilized Reactive Yellow 13. Measurement of trace-amounts of dye leaching from affinity columns is important because of possible toxicity or side effects linked with the presence of dye in therapeutic transthyretin preparations. A competitive enzyme immunoassay was developed to monitor yellow-dye column leaching. Biotinylated rabbit anti-Reactive Yellow 13 antibodies (immunoglobulin G fraction) were used as principal reagent. The assay is specific sensitive to 1 ng/ml of Reactive Yellow 13, has a good reproducibility and allows the accurate detection of the dye in the presence of transthyretin.

Transthyretin is an inhibitor of monocyte and endothelial cell interleukin-1 production

Human serum was found to contain an inhibitor of constitutive interleukin-1 (IL-1) production by human umbilical vein endothelial cells (ECs). Purification of the serum activity by anion exchange chromatography, molecular sieve HPLC, and hydroxyl apatite chromatography yielded material 82% pure with a molecular weight of 17 kDa by SDS-PAGE. Amino acid sequencing revealed the purified inhibitor to be transthyretin (TTR), a liver-derived protein. There was a 42.6% reduction in the production of spontaneous IL-1 activity in EC supernatants after coculture with 10 micrograms/ml TTR. TTR was subsequently found by ELISA to inhibit LPS-stimulated IL-1 production by cells of the human monocytic leukemia line THP-1 by 47.1 +/- 9.4%, whereas a less striking but still significant inhibition of monocyte-derived IL-1 beta production was also observed. Inhibition of IL-1 secretion correlated with increased IL-1 mRNA synthesis in both THP-1 cells and monocytes. Furthermore, TTR was associated with increased intracellular concentrations of IL-1 beta. These data suggest that TTR functions by inhibiting processing of newly synthesized peptide for secretion. This novel inhibitory effect of TTR on the production of IL-1 activity suggests a previously unrecognized endogenous antiinflammatory mediator.

Dye-affinity purification of transthyretin from an unexploited by-product of human plasma chromatographic fractionation

Dye-affinity chromatography of human plasma transthyretin on Remazol Yellow GGL-Sepharose from an unexploited by-product of chromatographic fractionation of plasma was optimized for large-scale preparation of a therapeutic product. With this system, transthyretin is only weakly bound to the gel. The residence time on gel and the transthyretin level in the by-product were observed to have no influence on the binding capacity of gel, and the optimum amount of transthyretin to be applied to the gel was found to be 1 g/l of gel. The adsorbent can be used more than ten times. The procedure resulted in the isolation, with a 30% yield with respect to plasma, of an 80% pure protein, which retained its thyroxine-binding capacity. Although the purity is acceptable for substitutive therapy, it can be improved further with a second chromatography on Cibacron Blue-Sepharose.

Two transthyretin variants (TTR Ala-49 and TTR Gln-89) in two Sicilian kindreds with hereditary amyloidosis

We report the biochemical and molecular characterization of two new transthyretin (TTR) variants in two Italian families with hereditary amyloidosis. Both families presented neuropathy and cardiomyopathy but they differ in other clinical features. These TTR variants were previously detected by isoelectric focusing (IEF); one is a neutral TTR variant and the other one is basic. By protein and DNA analysis the neutral variant was found to have a substitution of an alanine for a threonine residue at position 49 (TTR Ala-49) of the polypeptide chain. The basic variant has a glutamine residue replacing glutamate at position 89 (TTR Gln-89).

Purification of the isoforms of tear specific prealbumin

A chromatographic method for separating tear specific prealbumin (TSP) into six isoelectric forms is described. Size exclusion high performance liquid chromatography (SE-HPLC) was used to isolate TSP from whole tears, followed by chromatofocusing fast protein liquid chromatography (FPLC) of the SE-TSP fraction on a Mono P column. This yielded six fractions varying in isoelectric point (pI) between 5.3 and 4.6. Subsequent anion exchange FPLC (Mono Q column) allowed a slight further purification of each Mono P fraction and removed Polybuffer from the Mono P fractions. Isoelectric focusing (IEF) of the TSP isoforms verified that the heterogeneity was based on pI, and confirmed that the chromatofocusing separation was in many respects the same as an IEF separation. Purity of TSP isoforms was determined by SDS-polyacrylamide gel electrophoresis (SDS-PAGE), IEF, enzyme-linked immunosorbent assay (ELISA) and immunoblotting of samples separated by SDS-PAGE and IEF. Amino acid analysis and N-terminal amino acid sequencing revealed subtle differences between the TSP isoforms. The entire purification procedure was conducted both with and without the addition of reducing agents and protease inhibitors to tear samples and all buffers used in the purification process. Relatively little difference was seen in the TSP isoform profile under these two sets of conditions. However, the tendency of isolated TSP to aggregate and precipitate was dramatically decreased under reducing conditions, resulting in significantly higher protein recoveries. This chromatographic purification procedure provides a basis for further study of the nature of the heterogeneity of TSP and characterization of the properties of this protein.

[Diagnosis of familial amyloid polyneuropathy--gene analysis with primer-directed enzymatic amplification of DNA, isolation of plasma variant prealbumin and immunohistochemical identification of tissue amyloid protein]

Type I familial amyloid polyneuropathy (FAP) is an autosomal dominant hereditary generalized amyloidosis characterized by polyneuropathy and autonomic nerve failure. The main component of the amyloid fibril protein in this disorder has been shown to be a variant prealbumin with a single substitution of a methionine residue for valine at position 30. In the present study we have investigated 19 patients with FAP aged 31 to 67 and an asymptomatic family member using gene analysis with primer-directed enzymatic amplification (PCR) of DNA, isolation of plasma variant prealbumin and immunohistochemical identification of tissue amyloid protein. All patients and a symptom-free boy in the affected family had the mutant prealbumin gene showing abnormal DNA fragments by treatment with restriction endonuclease Bal I, and plasma variant prealbumin was also detected in all of them by reverse-phase high performance liquid chromatography. Rectum biopsies obtained from 9 patients showed amyloid deposits which were specifically immunostained by anti-human prealbumin antiserum. However, an asymptomatic carrier at the age of 16 showed no rectal amyloid deposition. Recent studies of FAP have disclosed that the expression of type I FAP is closely associated with the gene mutation of prealbumin. Accordingly, a simple and rapid method to detect this gene abnormality using PCR technique is considered to be very useful for diagnosis of type I FAP and can also provide valuable information for the genetic counselling of the family members at risk.

Evaluation of countermeasures for reduction of mouse airborne allergens

Three kinds of countermeasures for reduction of mouse airborne allergens were evaluated with use of an air sampler and immunochemical methods. Mouse cages and the sampler were placed inside a flexible-film isolator, and concentrations of mouse major allergens in the air were measured. The levels of the airborne allergens, prealbumin and albumin, generated by 10 males, were 3,050 and 492 pg/m3, respectively. Those by 10 females were lower, 317 and 270 pg/m3, respectively. When mouse cages were covered with a filter cap, the airborne allergens inside the isolator were decreased by 90%. When corncob was used as bedding in place of wood shavings, the airborne allergens were decreased by 57 and 77%, respectively. Therefore, for reduction of mouse airborne allergens, we recommend using female mice, covering the cages with filter caps, and using corncob bedding.