High-level production of functional muscle alpha-tropomyosin in Pichia pastoris

Auto-induction for high yield expression of recombinant novel isoallergen tropomyosin from King prawn (Melicertus latisulcatus) for improved diagnostics and immunotherapeutics

Food allergies are increasing worldwide, demonstrating a considerable public health concern. Shellfish allergy is one of the major food groups causing allergic sensitization among adults and children, affecting up to 2% of the general world population. Tropomyosin (TM) is the major allergen in shellfish and frequently used in the diagnosis of allergic sensitization and the detection of cross-contaminated food. To improve and establish better and more sensitive diagnostics for allergies and immunotherapeutics, large quantities of pure allergens are required. To establish a reproducible method for the generation of pure recombinant tropomyosin we utilized in this study different Escherichia coli strains (NM522, TOP10 and BL21(DE3)RIPL). In addition, isopropyl-β-D-thiogalactoside (IPTG) induction was compared with a novel auto-induction system to allow the generation of larger quantities of recombinant allergen. We demonstrated that the B-strain of E. coli is better for the expression of TM compared to the K-strain. Moreover, a higher yield could be achieved when using the auto-induction system, with up to 62 mg/l. High yield expressed recombinant TM from King prawn (KP) was compared to recombinant TM from Black tiger prawn (Pen m 1). We demonstrated that recombinant TM from KP and known isoallergen Pen m 1 have very similar molecular and immunological characteristics. Overall, we demonstrate that auto-induction can be used to express larger quantities of recombinant allergens for the development of diagnostic, to quantify allergens as well as immunotherapeutics employing isoallergens.

Tropomyosin: double helix from the protein world

This review concerns the structure and functions of tropomyosin (TM), an actin-binding protein that plays a key role in the regulation of muscle contraction. The TM molecule is a dimer of α-helices, which form a coiled-coil. Recent views on the TM structure are analyzed, and special attention is concentrated on those structural traits of the TM molecule that distinguish it from the other coiled-coil proteins. Modern data are presented on TM functional properties, such as its interaction with actin and ability to move on the surface of actin filaments, which underlies the regulation of the actin-myosin interaction upon contraction of skeletal and cardiac muscles. Also, part of the review is devoted to analysis of the effects of mutations in TM genes associated with muscle diseases (myopathies) on the structure and functions of TM.

Suitability of yeast- and Escherichia coli-expressed hepatitis B virus core antigen derivatives for detection of anti-HBc antibodies in human sera

Antibody to hepatitis B virus core antigen (anti-HBc) is one of the most important serological markers during hepatitis B virus (HBV) infection. The quality of the hepatitis B virus core antigen (HBcAg; diagnostic antigen) is crucial to the accuracy of anti-HBc detection. In an attempt to explore the suitability of recombinant HBcAg (rHBcAg) for diagnostic purposes, HBcAg was expressed in Escherichia coli (E. coli) and Pichia pastoris (P. pastoris) and evaluated for the detection of anti-HBc. The expression level of the recombinant protein satisfied the criteria for large-scale biologic production. P. pastoris- and E. coli-derived rHBcAg were purified with gel filtration followed by sucrose gradient (reagents A and C) or with a monoclonal anti-HBc antibody binding (reagents B and D) and were utilized to detect anti-HBc in competitive inhibition enzyme-linked immunosorbent assay (ELISA) format. The ELISA using P. pastoris-derived rHBcAg had a higher specificity and sensitivity than that using E.coli-derived rHBcAg to detect the anti-HBc standard panel. Serum specimens were collected from HBV-infected patients and healthy individuals (voluntary blood donors). Anti-HBc was detected in those specimens using P. pastoris- and E. coli-derived rHBcAg. The positive rate of anti-HBc detection in HBV-infected patients' sera was 100% with reagents A and B, 96.4% with reagent C, and 93.6% with reagent D. The negative rate in healthy control sera was 100% with reagents A and B, 97.0% with reagent C, and 99.7% with reagent D. These data indicate that P. pastoris-derived rHBcAg is superior to E.coli-derived rHBcAg for the detection of anti-HBc using the diagnostic ELISA.

Effects of cardiomyopathic mutations on the biochemical and biophysical properties of the human alpha-tropomyosin

Mutations in the protein alpha-tropomyosin (Tm) can cause a disease known as familial hypertrophic cardiomyopathy. In order to understand how such mutations lead to protein dysfunction, three point mutations were introduced into cDNA encoding the human skeletal tropomyosin, and the recombinant Tms were produced at high levels in the yeast Pichia pastoris. Two mutations (A63V and K70T) were located in the N-terminal region of Tm and one (E180G) was located close to the calcium-dependent troponin T binding domain. The functional and structural properties of the mutant Tms were compared to those of the wild type protein. None of the mutations altered the head-to-tail polymerization, although slightly higher actin binding was observed in the mutant Tm K70T, as demonstrated in a cosedimentation assay. The mutations also did not change the cooperativity of the thin filament activation by increasing the concentrations of Ca2+. However, in the absence of troponin, all mutant Tms were less effective than the wild type in regulating the actomyosin subfragment 1 Mg2+ ATPase activity. Circular dichroism spectroscopy revealed no differences in the secondary structure of the Tms. However, the thermally induced unfolding, as monitored by circular dichroism or differential scanning calorimetry, demonstrated that the mutants were less stable than the wild type. These results indicate that the main effect of the mutations is related to the overall stability of Tm as a whole, and that the mutations have only minor effects on the cooperative interactions among proteins that constitute the thin filament.

Expression of tropomyosin from Blattella germanica as a recombinant non-fusion protein in Pichia pastoris and comparison of its IgE reactivity with its native counterpart

Tropomyosins derived from invertebrates are well-known pan allergens. However, the allergenicities of recombinant tropomyosins are variable. Here, we undertook to compare the IgE-binding reactivities of native and recombinant German cockroach tropomyosins. Native tropomyosin was purified by ammonium sulfate fractionation, hydroxyapatite column chromatography, and electroelution, and recombinant tropomyosin was expressed in Pichia pastoris. The allergenicities of the native and recombinant tropomyosins were compared by ELISA inhibition analysis. Native German cockroach tropomyosin showed 18% IgE-binding reactivity to German cockroach sensitized sera. Recombinant tropomyosin was produced without fusion protein and its N-terminus was blocked like that of the native counterpart. The IgE-binding reactivity of the recombinant was found to be comparable to that of native tropomyosin over the concentration range 1-1000 ng/ml by ELISA inhibition testing. Recombinant German cockroach tropomyosin expressed in Pichia pastoris showed better allergenicity than that expressed in Escherichia coli. Other factors in addition to the structural differences of native and recombinant proteins may also influence the IgE reactivities of tropomyosins.

Conditions affecting production of functional muscle recombinant alpha-tropomyosin in Saccharomyces cerevisiae

Yeasts are attractive hosts for heterologous protein production as they follow the general eukaryotic post-translational modification pattern. The well-known Saccharomyces cerevisiae has been used to produce a large variety of foreign proteins. The proper function of muscle tropomyosin depends on a specific modification at its N-terminus. Although tropomyosin has been produced in different expression systems, only the recombinant protein produced in the yeast Pichia pastoris has native-like functional properties. In this paper we describe the production of functional skeletal muscle tropomyosin in the yeast S. cerevisiae. The recombinant protein was produced in high amounts and production was strongly affected by genetic and environmental factors, including plasmid copy number, promoter strength, and growth media composition.

Expression and biological activity of Baculovirus generated wild-type human slow alpha tropomyosin and the Met9Arg mutant responsible for a dominant form of nemaline myopathy

We have previously reported a Met9Arg mutation in the human skeletal muscle alpha tropomyosin gene (TPM3) associated with autosomal dominant nemaline myopathy [Nat. Genet. 9 (1995) 75]. We describe here the generation of wild-type (Wt-tpm3) and Met9Arg (M9R-tpm3) mutant human skeletal muscle slow alpha tropomyosin using the Baculovirus expression vector system (BEVS). This system produces correct posttranslationally modified recombinant tropomyosin proteins in insect cells. We show that the interactions of Wt-tpm3 with actin and tropomyosin are comparable to those of fast alpha tropomyosin isolated from chicken striated muscle. However, the recombinant M9R-tpm3 is at least 100 times less effective at binding actin than Wt-tpm3. This paper represents the first study of this mutation directly on the human isoform of tropomyosin that is involved in nemaline myopathy. It also represents the first time that human tpm3 has been produced using BEVS. This system can now be used to accurately demonstrate the effect of this (and other disease-associated tropomyosin mutations) on the interactions of tpm3 with the other protein components of the muscle thin filament, including those responsible for differing forms of nemaline myopathy.

Quantitative analysis of tropomyosin linear polymerization equilibrium as a function of ionic strength

Tropomyosin is a coiled-coil protein that polymerizes by head-to-tail interactions in an ionic strength-dependent manner. We produced a recombinant full-length chicken alpha-tropomyosin containing a 5-hydroxytryptophan residue at position 269 (formerly an alanine), 15 residues from the C terminus, and show that its fluorescence intensity specifically reports tropomyosin head-to-tail interactions. We used this property to quantitatively study the monomer-polymer equilibrium in tropomyosin and to calculate the equilibrium constant of the head-to-tail interaction as a function of ionic strength. Our results show that the affinity constant changes by almost 2 orders of magnitude over an ionic strength range of 50 mm (between I = 0.045 and 0.095). We were also able to calculate the average polymer length as a function of concentration and ionic strength, which is an important parameter in the interpretation of binding isotherms of tropomyosin with other thin filament proteins such as actin and troponin.