Fluorescent hollow ZrO2@CdTe nanoparticles-based lateral flow assay for simultaneous detection of C-reactive protein and troponin T

Highly fluorescent hollow ZrO₂@CdTe nanoparticles (NPs) were synthesized efficiently via the hydrothermal method. By changing the hydrothermal time of ZrO₂@CdTe NP, the peaks of fluorescence spectra measured at fluorescent excitation of 330 nm were at 540 nm, 590 nm, and 640 nm, respectively. Hollow ZrO₂ NPs have a uniform core-shell structure with the size of 178 ± 10 nm and shell of 19 ± 4 nm. The as-prepared yellow-ZrO₂@CdTe NPs were used to develop lateral flow assay (LFA) for the sensitive and qualitative detection of C-reactive protein (CRP). The visual limit of detection of the LFA for the CRP antigen was 1 μg/L within 20 min, which is 1000-fold lower than that of colloidal gold-based LFA. In addition, a multiplex lateral flow assay (mLFA) was developed using the as-prepared green and red-ZrO₂@CdTe NPs for the simultaneous, specific, sensitive, and qualitative detection of CRP and troponin T (cTnT). The visual limits of detection of CRP and cTnT in mLFA were 10 μg/L and 0.1 mg/L, respectively. The excellent performance of ZrO₂@CdTe NPs should facilitate their application in point-of-care technology for the detection of other biomarkers.

Molecular characterization of troponin T in Scylla paramamosain and its role in Vibrio alginolyticus and white spot syndrome virus (WSSV) infection

This study investigated the function of Troponin T (TnT) in the mud crab, Scylla paramamosain. The 1952 bp cDNA sequence of TnT was cloned from S. paramamosain using rapid amplification of cDNA ends (RACE) PCR. The quantitative real-time PCR analysis showed that TnT was highly expressed in the muscle and heart of S. paramamosain. Challenging with white spot syndrome virus (WSSV) or Vibrio alginolyticus (VA), two common pathogens that infect mud crabs, enhanced the expression of TnT in S. paramamosain. Knockdown of TnT using TnT-dsRNA led to up-regulating the expression of immune-related genes, such as c-type-lectin, toll-like-receptor, crustin antimicrobial peptide and prophenoloxidase. The cumulative mortality of WSSV- and VA-infected crabs was significantly increased following TnT knockdown. After WSSV or VA infection, TnT knockdown caused a significant reduction in phenoloxidase (PO) activity, superoxide dismutase (SOD) activity and total hemocyte count (THC), indicating a regulatory role of TnT in the innate immune response of S. paramamosain to pathogens. Apoptosis of hemocytes was higher in crabs treated with TnT-dsRNA compared with control crabs treated with phosphate-buffered saline. Knockdown of TnT increased apoptosis of hemocytes following VA infection, but reduced hemocyte apoptosis following WSSV infection. In summary, TnT may enhance the immune response of S. paramamosain to WSSV infection by regulating apoptosis, THC, PO activity and SOD activity. And TnT may play a positive role in the immune response against VA infection by regulating apoptosis, THC, SOD activity and PO activity.

Paper-based cascade cationic isotachophoresis: Multiplex detection of cardiac markers

Paper-based analytical devices (PADs) are widely used in point-of-care testing (POCT) as they are cost-effective, simple and straightforward. However, poor sensitivity hinders their use in detecting diseases with low abundance biomarkers. The poor detection limit of PADs is mainly attributed to the low concentration of analytes, and the complexity of biological fluid, leading to insufficient interactions between analytes and capture antibodies. This study aims to overcome these difficulties by developing a paper-based cationic isotachophoresis (ITP) approach for simultaneously detecting pico-molar levels of two essential cardiac protein markers: acidic troponin T (cTnT) and basic troponin I (cTnI) spiked into human serum samples. The approach utilizes 3-aminopropyltrimethoxysilane (APTMS) treated glass fiber papers with decreasing cross-sectional area assembled on a 3D printed cartridge device. Our results showed that in the presence of cTnT monoclonal antibody (mAb), fluorescently labeled cTnI and cTnT could be effectively enriched in cationic ITP. Each individual target was captured subsequently by a test line in the detection zone where the capture mAb was immobilized. Detailed analysis suggests that the technology is capable of simultaneous on-board depletion of abundant plasma proteins and enrichment of cTnI/cTnT by ~1300-fold with a sensitivity of 0.6 pmol/L for cTnT and a sensitivity of 1.5 pmol/L for cTnI in less than 6 min. The results demonstrate the potential of this technology for rapid, ultra-sensitive and cost-effective analysis of multiplex protein markers in clinical serum samples at point of care.

Mechanism of interference by haemolysis in the cardiac troponin T immunoassay

Background: The cardiac troponins have been shown to be sensitive and specific biochemical markers of myocardial infarction and highly prognostic for future adverse events in patients with acute coronary syndromes. There have been reports suggesting that haemolysis causes a negative interference in the cardiac troponin T (cTnT) assay but the mechanism(s) involved remain unknown. Here we show the effects of haemolysis and haemoglobin per se on the cTnT assay.

Methods: The effect of haemolysis was studied by the addition of prepared haemolysate to serum samples with known and clinically relevant cTnT levels. The effect of haemoglobin was studied by the addition of haemoglobin of increasing concentrations and noting its effect on the level of cTnT measured. The effect of putative proteases was determined indirectly by incubating samples with spiked cTnT with various protease inhibitors and observing the changes in the measured cTnT levels.

Results: The results show that both haemolysis, which is the release of haemoglobin and corpuscular contents, and haemoglobin itself negatively interfere in the cTnT assay in a concentration-dependent manner, although the former had a greater magnitude of effect. On haemolysis, indirect evidence suggests that proteases are released which degrade the cTnT in serum, thus causing the decreased levels detected. Pepstatin A, a reversible inhibitor of aspartic proteinases, effectively inhibited the loss of cTnT in serum at 37°C and pH 7.4 over a 48-h period. We found that at a haemoglobin level of 0.75 g/L, cTnT declined by more than 10% of the initial concentration, suggesting that falsely decreased levels due to haemolysis may significantly affect the clinical utility of the assay.

Conclusions: Haemolysis, haemoglobin per se and possibly proteolysis play a role in the negative interference in cTnT assays. Measures to reduce this interference must be implemented.

[Cloning, expression and immuno-protection analysis of a gene encoding troponin T of Schistosoma japonicum (SjTnT)]

OBJECTIVE

To clone cDNA encoding troponin T of Schistosoma japonicum (SjTnT), and evaluate the protective efficacy induced by recombinant SjTnT in BALB/c mice against S. japonicum challenge infection.

METHODS

The SjTnT gene was amplified from 28-day-schistosome cDNAs by PCR and then subcloned into pET28a(+). The recombinant SjTnT protein (rSjTnT) was expressed in Escherichia coli BL21 (DE3) cells. The serum specific to rSjTnT was prepared by immunized BALB/c mice with the recombinant antigen, and the immunogenicity of rSjTnT was detected by Western blotting and ELISA. The immuno-protective efficacy induced by rSjTnT in BALB/c mice was evaluated according to the reduction in worm and egg counts.

RESULTS

The cDNA encoding SjTnT was successfully cloned and expressed in E. coli. Western blotting showed that rSjTnT had a good immunogenicity. The high level of specific IgG antibodies was detected, and 33.89% worm reduction and 43.94% liver egg reduction were obtained in mice vaccinated with rSjTnT combined with Seppic 206 adjuvant compared with those in the adjuvant control group.

CONCLUSIONS

rSjTnT could induce partial immuno-protection against S. japonicum infection in BALB/c mice. This study provided a basic for understanding the biological function of SjTnT.

Troponin and anti-troponin autoantibody levels in patients with ventricular noncompaction

Ventricular hypertrabeculation/noncompaction is a morphologic and functional anomaly of myocardium characterized by prominent trabeculae accompanied by deep recessus. Dilated cardiomyopathy with left ventricular failure is observed in these patients, while the cause or pathophysiologic nature of this complication is not known. Anti-troponin antibodies are formed against circulating cardiac troponins after an acute coronary event or conditions associated with chronic myocyte necrosis, such as dilated cardiomyopathy. In present study, we aimed to investigate cardiac troponins and anti troponin autoantibodies in ventricular noncompaction/hypertrabeculation patients with/without reduced ejection fraction. A total of 50 patients with ventricular noncompaction and 23 healthy volunteers were included in this study. Noncompaction/hypertrabeculation was diagnosed with two-dimensional echocardiography using appropriate criteria. Depending on ejection fraction, patients were grouped into noncompaction with preserved EF (LVEF >50%, n = 24) and noncompaction with reduced EF (LVEF <35%, n = 26) groups. Troponin I, troponin T, anti-troponin I IgM and anti-troponin T IgM were measured with sandwich immunoassay method using a commercially available kit. Patients with noncompaction had significantly higher troponin I (28.98±9.21 ng/ml in NCNE group and 28.11±10.42 ng/ml in NCLE group), troponin T (22.17±6.97 pg/ml in NCNE group and 22.78±7.76 pg/ml in NCLE group) and antitroponin I IgM (1.92±0.43 µg/ml in NCNE group and 1.79±0.36 µg/ml in NCLE group) levels compared to control group, while antitroponin T IgM and IgG were only elevated in patients with noncompaction and reduced EF (15.81±6.52 µg/ml for IgM and 16.46±6.25 µg/ml for IgG). Elevated cardiac troponins and anti-troponin I autoantibodies were observed in patients with noncompaction preceding the decline in systolic function and could indicate ongoing myocardial damage in these patients.

A nanostructured piezoelectric immunosensor for detection of human cardiac troponin T

A piezoelectric immunosensor based on gold nanoparticles (AuNPs) co-immobilized on a dithiol-modified surface is proposed for detection of human cardiac troponin T (TnT). Anti-human troponin T (anti-TnT) antibodies were covalently immobilized on the nanostructured electrode surface by thiol-aldehyde linkages. In a homogeneous bulk solution, TnT was captured by anti-TnT immobilized on the QCM electrode. Cyclic voltammetry studies were used to characterize the AuNPs layer on the electrode surface and the anti-TnT immobilization steps. The QCM-flow immunosensor exhibited good reliability, measuring concentrations of TnT from 0.003 to 0.5 ng mL(-1) in human serum with high linearity (r = 0.989; p < 0.01). The immunosensor exhibited a 7% coefficient of variation and 0.0015 ng mL(-1) limit of detection, indicating a high reproducibility and sensitivity. The proposed QCM nanostructured immunosensor is easy to use and has promising potential in the diagnosis of acute myocardial infarction due to its speed and high sensitivity.

Native troponin-T of the American cockroach (CR), Periplaneta americana, binds to IgE in sera of CR allergic Thais

The American cockroach, Periplaneta americana, is the predominant cockroach (CR) species in Thailand and a major source of indoor allergens second only to the house dust mite. The incidence of CR allergy among allergic Thai patients is increasing but basic information on the allergenic components is scarce. In this study a recombinant troponin-T was produced by using cDNA prepared from RNA of the P. americana as a template and PCR primers designed from the P. americana troponin-T sequence deposited in the GenBank database. The recombinant protein (Mr approximately 50) did not bind to IgE in the sera of 18 skin prick test positive CR allergic patients. Rabbit polyclonal antiserum (PAb) against the recombinant troponin-T was produced and used in preparing an affinity column for the purification of native troponin-T from the crude P. americana extract (Mr approximately 47). IgE-immunoblotting revealed that the native protein bound to IgE in 3 of the 18 (16.7%) patients. Our results imply that native P. americana troponin-T, but not its recombinant counterpart, is a minor allergen among the CR allergic Thais.

Tissue-specific interactions of TNI isoforms with other TN subunits and tropomyosins in C. elegans: the role of the C- and N-terminal extensions

The aim of this study is to investigate the function of the C-terminal extension of three troponin I isoforms, that are unique to the body wall muscles of Caenorhabditis elegans and to understand the molecular interactions within the TN complex between troponin I with troponin C/T, and tropomyosin. We constructed several expression vectors to generate recombinant proteins of three body wall and one pharyngeal troponin I isoforms in Escherichia coli. Protein overlay assays and Western blot analyses were performed using antibodies. We demonstrated that pharyngeal TNI-4 interacted with only the pharyngeal isoforms of troponin C/T and tropomyosin. In contrast, the body wall TNI-2 bound both the body wall and pharyngeal isoforms of these components. Similar to other invertebrates, the N-terminus of troponin I contributes to interactions with troponin C. Full-length troponin I was essential for interactions with tropomyosin isoforms. Deletion of the C-terminal extension had no direct effect on the binding of the body wall troponin I to other muscle thin filament troponin C/T and tropomyosin isoforms.

Mass spectrometric approaches for elucidation of antigenantibody recognition structures in molecular immunology

Mass spectrometric approaches have recently gained increasing access to molecular immunology and several methods have been developed that enable detailed chemical structure identification of antigen-antibody interactions. Selective proteolytic digestion and MS-peptide mapping (epitope excision) has been successfully employed for epitope identification of protein antigens. In addition, "affinity proteomics" using partial epitope excision has been developed as an approach with unprecedented selectivity for direct protein identification from biological material. The potential of these methods is illustrated by the elucidation of a beta-amyloid plaque-specific epitope recognized by therapeutic antibodies from transgenic mouse models of Alzheimer's disease. Using an immobilized antigen and antibody-proteolytic digestion and analysis by high resolution Fourier transform ion cyclotron resonance mass spectrometry has lead to a new approach for the identification of antibody paratope structures (paratope-excision; "parex-prot"). In this method, high resolution MS-peptide data at the low ppm level are required for direct identification of paratopes using protein databases. Mass spectrometric epitope mapping and determination of "molecular antibody-recognition signatures" offer high potential, especially for the development of new molecular diagnostics and the evaluation of new vaccine lead structures.

Cardiac troponin I but not cardiac troponin T induces severe autoimmune inflammation in the myocardium

BACKGROUND

Cardiac troponins in blood are the most preferred markers of myocardial damage. The fact that they are normally not found in the circulation provides a high level of clinical sensitivity and specificity even when cardiac lesions are small. After myocardial injury, the troponins enter the circulation, where they can be used for diagnosis of acute coronary syndromes. Thus, the cardiac troponins are paramount for disease classification and risk stratification. However, little is known about the long-term effects of the released troponins on cardiac function.

METHODS AND RESULTS

In this study we prepared recombinant murine cardiac troponin I (mc-TnI) and murine cardiac troponin T and used them to immunize mice. We report that A/J mice immunized with mc-TnI developed severe inflammation of the myocardium with increased expression of inflammatory chemokines RANTES (regulated on activation normal T cell expressed and secreted), monocyte chemoattractant protein-1, macrophage inflammatory protein (MIP)-1alpha, MIP-1beta, MIP-2, T-cell activation gene 3, and eotaxin and chemokine receptors CCR1, CCR2, and CCR5. The inflammation was followed by cardiomegaly, fibrosis, reduced fractional shortening, and 30% mortality over 270 days. In contrast, mice immunized with murine cardiac troponin T or with the control buffer showed little or no inflammation and no death. Furthermore, we demonstrate that mice preimmunized with mc-TnI before left anterior descending coronary artery ligation showed greater infarct size, more fibrosis, higher inflammation score, and reduced fractional shortening.

CONCLUSIONS

Overall, our results show for the first time that provocation of an autoimmune response to mc-TnI induces severe inflammation in the myocardium followed by fibrosis and heart failure with increased mortality in mice.

"Affinity-proteomics": direct protein identification from biological material using mass spectrometric epitope mapping

We describe here a new approach for the identification of affinity-bound proteins by proteolytic generation and mass spectrometric analysis of their antibody bound epitope peptides (epitope excision). The cardiac muscle protein troponin T was chosen as a protein antigen because of its diagnostic importance in myocardial infarct, and its previously characterised epitope structure. Two monoclonal antibodies (IgG1-1B10 and IgG1-11.7) raised against intact human troponin T were found to be completely cross reactive with bovine heart troponin T. A combination of immuno-affinity isolation, partial proteolytic degradation (epitope excision), mass spectrometric peptide mapping, and database analysis was used for the direct identification of Tn T from bovine heart cell lysate. Selective binding of the protein was achieved by addition of bovine heart cell lysate to the Sepharose-immobilised monoclonal antibodies, followed by removal of supernatant material containing unbound protein. While still bound to the affinity matrix the protein was partially degraded thereby generating a set of affinity-bound, overlapping peptide fragments comprising the epitope. Following dissociation from the antibody the epitope peptides were analysed by matrix assisted laser desorption-ionisation (MALDI) and electrospray-ionisation (ESI) mass spectrometry. The peptide masses identified by mass spectrometry were used to perform an automated database search, combined with a search for a common "epitope motif". This procedure resulted in the unequivocal identification of the protein from biological material with only a minimum number of peptide masses, and requiring only limited mass-determination accuracy. The dramatic increase of selectivity for identification of the protein by combining the antigen-antibody specificity with the redundancy of peptide sequences renders this "affinity-proteomics" approach a powerful tool for mass spectrometric identification of proteins from biological material.

A skeletal muscle troponin T specific ELISA based on the use of an antibody against the soluble troponin T (16-31) fragment

Proteolytic degradation of muscle, which occurs post-mortem as part of the meat-ageing process, results in the production of protein fragments. In beef, degradation of skeletal muscle troponin T (TnT) results in the generation of a 16-residue long peptide (TnT (16-31)), identified in trichloroacetic acid (TCA) soluble extracts. We report the development of a competitive enzyme-linked immunosorbent assay (ELISA) for the quantification of TnT (16-31), using polyclonal antibodies raised against synthetic TnT (16-31). The ELISA procedure is based on inhibition of binding of the antibodies to immobilised TnT (16-31) by TnT (16-31) present in solution. Its useful range is 30 pmol to 2 nmol TnT (16-31)/ml. Quantification of TnT (16-31) in TCA muscle extracts showed that its concentration was enhanced with ageing. Moreover, a correlation between TnT (16-31) levels and meat tenderness was observed. The ELISA developed herein may prove advantageous for future use at the research and industrial level.

Embryonic myosin heavy chain and troponin T isoforms remain in the cremaster muscle of adult rat cryptorchidism induced with flutamide

We examined the immunolocalization of isoforms of muscle proteins, myosin and troponin, in the cremaster muscle of the undescended testis (cryptorchidism). In cryptorchid rats induced by a nonsteroidal androgen antagonist, flutamide, the cremaster muscle contained embryonic myosin and embryonic/cardiac troponin T in both immunofluorescence microscopy and Western blotting using antibodies against myosin and troponin T specific for embryonic, cardiac and fast skeletal muscles. However, in muscles other than the cremaster muscle, i. e., the masseter, pectoral and abdominal muscles, embryonic isoforms of these proteins were undetectable by immunohistochemistry with these antibodies, even in the muscles from cryptorchid rats. Our results showing that high levels of embryonic isoforms of muscle proteins were specifically present in the cremaster muscle of cryptorchid rats induced by flutamide suggest that flutamide treatment of pregnant rats might affect genes controlling the development of the lumbar region of the fetus body resulting in the presence of embryonic protein isoforms in the cremaster muscles which are closely associated with undescended testes.

Evolution of a metal-binding cluster in the NH(2)-terminal variable region of avian fast skeletal muscle troponin T: functional divergence on the basis of tolerance to structural drifting

This study investigated the evolution of a transition metal ion-binding cluster ([H--X--X--X--H](n); Tx) in the alternatively spliced NH(2)-terminal variable region of avian pectoral muscle troponin T (TnT). Encoded by avian fast skeletal muscle TnT-specific P exons, Tx-like structures were expressed in the breast muscle TnT's of almost all birds examined. Their presence results in the developmentally up-regulated high molecular weight pectoral muscle TnT. Sequence analysis and metal affinity chromatography revealed that in Galliformes and Craciformes, the Tx structure evolved into multiple H--X--X--X--H pairs with a high-affinity metal-binding capacity. Turkey, chicken, quail, and curassow breast muscle TnT's contain nine, seven, four, and three consecutive or closely located metal-binding sites, respectively, in the NH(2)-terminal region. The metal-binding affinity of the Tx element increased as the number of His pairs increased due to the duplication of P exons and the conversion of other exon sequences. The data show two related components of avian pectoral muscle TnT evolution: a larger, more acidic NH(2)-terminal segment and a cluster of transition metal-binding sites, both of which may have functional significance for their selection value. The evolution of the Tx segment in the NH(2)-terminal variable region of avian pectoral muscle TnT demonstrates a functional divergence on the basis of tolerance to structural drifting.

Modulation of troponin T molecular conformation and flexibility by metal ion binding to the NH2-terminal variable region

Troponin T (TnT) plays an allosteric signal transduction role in the actin thin-filament-based Ca(2+)-regulation of striated muscle contraction. Developmentally regulated alternative RNA splicing produces TnT isoforms differing in their NH(2)-terminal structure. Physical property variations of the NH(2)-terminal hypervariable region of TnT may have a role in tuning the Ca(2+)-sensitivity and overall cooperativity of the muscle. We have previously demonstrated that metal ion or monoclonal antibody binding to the NH(2)-terminal region can modulate the epitopic conformation and troponin I and tropomyosin binding affinity of TnT. To further establish the molecular basis of this conformational and functional modulation, we have characterized the NH(2)-terminal variable region-originated secondary conformational effect in TnT using fluorescence spectral analysis. The chicken fast skeletal muscle TnT isoform, TnT8e16, containing a cluster of transition-metal ion binding sites (Tx) in the NH(2)-terminal variable region was used in this study. TnT8e16 was titrated for Cu(II) binding-induced changes in fluorescence intensity and anisotropy of the COOH-domain Trp residues (W234, W236, and W285), which demonstrated considerable environmental sensitivity in TnT denaturation studies. Nonlinear Stern-Volmer plots of Trp quenching indicated a metal ion binding-induced conformational change in TnT. Fluorescence anisotropy changes upon metal ion binding indicated a decrease in the mobility of the Trp residues and an increase in the flexibility of fluorescein-labeled Cys263 in the COOH domain. These data support a model that the alternatively spliced NH(2)-terminal variable region of TnT modulates conformation and flexibility of other domains of the protein.

Confocal imaging of early heart development in Xenopus laevis

Xenopus laevis provides a number of advantages to studies on cardiovascular development. The embryos are fairly large, are easy to obtain, and can develop at ambient temperature in simple buffer solutions. Although classic descriptions of heart development exist, the ability to use whole-mount immunohistochemical methods and confocal microscopy may enhance the ability to understand both normal and experimentally perturbed cardiovascular development. We have started to examine the early stages of cardiac development in Xenopus, seeking to identify antibodies and fixatives that allow easy examination of the developing heart. We have used monoclonal antibodies (mAbs) raised against bovine cardiac troponin T and chicken tropomyosin to visualize cardiac muscle, a goat antibody recognizing bovine type VI collagen to stain the lining of vessels, and the JB3 mAb raised against chicken fibrillin, which allows the visualization of a variety of cardiovascular tissues during early development. Results from embryonic stages 24-46 are presented.

Immunohistochemical studies on regulation of alternative splicing of fast skeletal muscle troponin T: non-uniform distribution of the exon x3 epitope in a single muscle fiber

Troponin T (TnT) isoforms of chicken fast skeletal muscle are classified into two types, breast-muscle-type (B-type) and leg-muscle-type (L-type) isoforms. These isoforms are produced from a single gene by differential alternative splicing of pre-mRNA. We investigated immunohistochemically the distribution of B-type TnT isoforms in chicken leg muscle (musculus biceps femoris), using anti-exon x3 that was raised against a synthetic peptide corresponding to exon x3 and recognized B-type, but not the L-type, TnT isoforms. Mosaic patterns of immunostaining showing locally different expression of B-type TnT isoforms in a single fiber were observed among fibers, and the non-uniform distribution of the isoforms was also detected in sectioned fibers and myofibrils from the muscle. The results indicated that regulation of pre-mRNA splicing of fast skeletal muscle TnT was different not only among the muscle fibers but also within a single fiber, suggesting that heterogeneous myonuclei in regulation of alternative splicings occur in a single muscle fiber.

Tissue-specific distribution of breast-muscle-type and leg-muscle-type troponin T isoforms in birds

In order to show the tissue-specific distribution of troponin T (TnT) isoforms in avian skeletal muscles, their expression was examined by electrophoresis of the breast and leg muscles of seven avian species and immunoblotting with the antiserum against fast skeletal muscle TnT. It has been reported in the chicken that breast-muscle-type (B-type) and leg-muscle-type (L-type) TnT isoforms are expressed specifically in the adult breast and leg muscles, respectively. Their differential expression patterns were confirmed in all birds examined in this study. The expression of a segment encoded by the exon x series of TnT was also examined by immunoblotting with the antiserum against a synthetic peptide derived from the exon x3 sequence, because the segment has been shown to be included exclusively in the B-type, but not in the L-type TnT. The expression of the segment was found only in the breast muscle, but not in the leg muscle of all birds examined. TnT cDNA sequences from the duck breast and leg muscles were determined and showed that only B-type TnT had an exon x-related sequence, suggesting that the expression of B-type TnT containing the exon x-derived segment is conserved consistently in the birds.

Degradation of cardiac troponin I: implication for reliable immunodetection

We have analyzed by different immunological methods the proteolytic degradation of cardiac troponin I (cTnI) in human necrotic tissue and in serum. cTnI is susceptible to proteolysis, and its degradation leads to the appearance of a wide diversity of proteolytic peptides with different stabilities. N- and C-terminal regions were rapidly cleaved by proteases, whereas the fragment located between residues 30 and 110 demonstrated substantially higher stability, possibly because of its protection by TnC. We conclude that antibodies selected for cTnI sandwich immunoassays should preferentially recognize epitopes located in the region resistant to proteolysis. Such an approach can be helpful for a much needed standardization of cTnI immunoassays and can improve the sensitivity and reproducibility of cTnI assays.

Conformational modulation of troponin T by configuration of the NH2-terminal variable region and functional effects

Troponin T (TnT) is an essential element in the thin filament-based regulatory system of striated muscle. Alternative mRNA splicing generates multiple TnT isoforms with primary structural differences in the NH2-terminal region. The functional significance of this hypervariable NH2-terminal domain and the developmental or muscle type-specific TnT isoforms is not fully understood. We have analyzed chicken breast muscle TnT containing a metal-binding cluster [H(E/A)EAH]4-7 (Tx) in the NH2-terminal region to demonstrate potential effects of the NH2-terminal structure on the conformation of TnT [Ogut, O., and Jin, J.-P. (1996) Biochemistry 35, 16581-16590]. Using specific antibody epitope analysis on this metal-binding TnT model, this study revealed that the binding of Zn2+ to the NH2-terminal region of chicken breast muscle TnT induces extensive conformational changes in the whole protein as demonstrated by a significant decrease in binding avidity of a polyclonal anti-TnT serum which recognizes multiple epitopes on the TnT molecule. This NH2-terminal configuration-based effect is not restricted to the metal ion interaction, whereas the binding of anti-NH2 terminus monoclonal antibodies to TnT induced similar changes. Protein-binding assays have shown that the NH2-terminal variability-induced conformational changes can alter TnT's binding affinity for tropomyosin and troponin I. The results suggest a functional modulation of TnT through the configuration of the NH2-terminal domain, and this novel mechanism may mediate the physiological significance of the TnT isoform regulation.