A recombinant monocysteine mutant (Ser to Cys-155) of fast skeletal troponin T: identification by cross-linking of a domain involved in a physiologically relevant interaction with troponins C and I

Troponin T (TnT), a subunit of the heterotrimeric troponin (Tn) complex, is essential for the Ca2+ regulation of vertebrate striated muscle contraction both in vivo and in vitro. With the exception of bovine cardiac TnT, all known vertebrate TnT isoforms lack a thiol group, a property which makes the wild-type proteins unsuitable as cross-linking substrate. We generated a mutant human fast skeletal TnT in which Ser155 was changed to Cys (TnT-Cys155). Mutation of this residue in TnT as well as in vitro expression in Escherichia coli and purification of the recombinant mutant protein did not affect its biological properties in terms of in vitro binding to troponin I (TnI), troponin C (TnC), actin-tropomyosin (actin-Tm), and actomyosin ATPase activity. TnT-Cys155 was labeled with 4-maleimidobenzophenone (BP-TnT155) and photo-cross-linked to TnI, TnC, Tm, and all of the thin filament proteins. BP-TnT155 did not cross-link to Tm and showed weak Ca2+/Mg2+-independent cross-linking with TnI in the binary complex and in the presence of all thin filament protein components. BP-TnT155 showed Ca2+/Mg2+-dependent cross-linking with TnC in the binary and ternary complexes and Ca2+-favored cross-linking with TnI in the ternary complex. Thus, residue 155 of TnT is within 10 A (the length of cross-linker) of TnC in the presence or absence of Ca2+ and comes within 10 A of both TnI and TnC in the presence of Ca2+. TnT residue 155 is in close proximity to or may even partly encompass the Tm binding site. These results suggest that TnT, in association with TnI, may participate in the "information transfer" mediated by the Ca2+ binding signal from TnC to Tm and the region around TnT residue 155 probably acts as a linker between troponin and actin-Tm in this signal transmission process. Our results also suggest that TnT contains at least one Ca2+/Mg2+-dependent TnC binding region located between its Tm and TnI binding regions. A recombinant truncated fragment of TnI, TnI96-181, containing amino acid residues 96-181 and labeled with BP at Cys-133, failed to cross-link with TnT, indicating that the region around Cys-133 of TnI is not involved in binary interaction with TnT.

Identification and mutagenesis of a highly conserved domain in troponin T responsible for troponin I binding: potential role for coiled coil interaction

Troponin T (TnT), a thin filament myofibrillar protein, is essential for the Ca2+ regulation of striated muscle contraction in vertebrates, both in vivo and in vitro. To understand the role of TnT in this process, its interaction with two other troponin components, troponin I (TnI) and troponin C (TnC) was examined by using the yeast two hybrid system, which is a genetic approach to detect protein-protein interactions. Computer assisted analysis of phylogenetically distant TnT amino acid sequences unveiled a highly conserved protein domain that is characterized by a heptad repeat (HR) motif with a potential for alpha-helical coiled coil formation. A similar, potentially coiled coil forming domain is also conserved in all known TnI sequences. These protein motifs appeared to be the regions where TnI-TnT interaction may take place. Deletions and point mutations in TnT, which disrupted its HR motif, severely reduced or abolished TnI binding, but binding to TnC was not affected, indicating that the TnT-TnI and TnT-TnC binary interactions can be uncoupled. Remarkably, the truncated fragments of TnT and TnI in which the HR motifs were retained showed binary interaction in the yeast two hybrid system. It was also observed that the formation of the TnT-TnI heterodimers is favored over the homodimers TnT-TnT and TnI-TnI. These results indicate that the evolutionarily conserved HR motifs may play a role in TnT-TnI dimerization, presumably through the formation of alpha-helical coiled coils.

DNA sequencing and comparative sequence analysis reveal that the Escherichia coli genomic DNA may replace the target DNA during molecular cloning: evidence for the erroneous assembly of E. coli DNA into database sequences

DNA sequencing and similarity search of databases provide experimental evidence that portions of the host Escherichia coli genome may get ligated into the cloning vector, resulting in clones containing nontargeted inserts. Several lines of evidence suggest that this non-targeted ligation, as observed by us while subcloning troponin I cDNA, is presumably due to a recombination-mediated mechanism by which host DNA replaces the target DNA in the cloning vector. The E. coli genome mapping to 64-65 min and 92.8-00.1 min, the latter containing insertion sequences, appears to be the hotspot regions involved in this process. We examined the possibility that some sequences reported in the databases may also contain genomic sequences of E. coli. A search of current databases revealed that a rat hepatic glutathione transporter cDNA contains a 2.2-kb-long portion of the E. coli genome that has been wrongly assembled into its 5' untranslated and coding regions. In addition, about 30 sequences in databases, including a Yersinia pestis toxin gene, showed relatively high sequence identity with those portions of the E. coli genome that were present in the nonauthentic clones.

Interaction of deletion mutants of troponins I and T: COOH-terminal truncation of troponin T abolishes troponin I binding and reduces Ca2+ sensitivity of the reconstituted regulatory system

The interaction between troponin I (TnI) and troponin T (TnT) remains the least understood binary interaction among the regulatory proteins of vertebrate striated muscle. To identify the specific binding domains of TnI and TnT and to evaluate the interactions of TnT with troponin C and tropomyosin (Tm), we generated an NH2-terminal fragment of human fast skeletal beta TnT (TnT1-201; residues 1-201) using site-directed mutagenesis. The mutant protein failed to bind to rabbit skeletal muscle TnI as judged by HPLC, showed reduced TnC binding and reduced ternary troponin (Tn) complex formation, and exhibited a much reduced Ca2+ sensitivity in the reconstituted regulatory system. It is shown that the amount of Tn complex formed by TnT1-201 rather than the activity of the mutant Tn complex affected this Ca2+ sensitivity. Binding of the mutant to Tm was similar to that of intact TnT. These results support the view that the COOH-terminal segment of TnT is necessary for binding to TnI and TnC and Ca2+ sensitivity in the thin filament, whereas its NH2-terminus strongly binds to Tm. To identify the regions of TnI which bind to muscle TnT, we used four recombinant fragments of fast skeletal muscle TnI containing amino acid residues 1-94 (TnI1-94), 1-120 (TnI1-120), 96-181 (TnI96-181), and 122-181 (TnI122-181) and a synthetic peptide, TnI98-114, containing residues 98-114 corresponding to the inhibitory region. Only TnI1-120 showed weak binding to TnT but not to TnT1-201. These results suggest that (i) a region within the NH2-terminal 120 residues of TnI interacts with TnT and (ii) the COOH-terminal residues 202-258 of TnT contain the interaction site of TnI. Overall, our results also imply that residues 159-201 constitute the smallest region of TnT which contributes to the Ca2+ sensitivity of actoS1 ATPase in a reconstituted regulatory system.

Photo-cross-linking of rabbit skeletal troponin I deletion mutants with troponin C and its thiol mutants: the inhibitory region enhances binding of troponin I fragments to troponin C

Contraction of vertebrate striated muscle is regulated by the strong Ca(2+)-dependent interaction between troponin I (TnI) and troponin C (TnC). To critically evaluate this interaction, we generated four recombinant deletion fragments of rabbit fast skeletal TnI: the NH2-terminal fragment (TnI1-94), the NH2 terminus and the inhibitory region (TnI1-120), the inhibitory region and the COOH terminus (TnI96-181), and the COOH-terminal fragment (TnI122-181) containing amino acid residues 1-94, 1-120, 96-181, and 122-181, respectively. Native TnC and seven thiol mutants, containing single cysteine residues in the two globular domains and in the central helix of TnC, e.g., Cys-12, Cys-21, Cys-57, Cys-89, Cys-122, Cys-133, and Cys-158, were labeled with 4-maleimidobenzophenone, and their interaction with the recombinant TnI fragments and the synthetic inhibitory peptide (TnI98-114, residues 98-114) was studied by photo-cross-linking. Extensive cross-linking occurred between various domains of TnC and TnI. The cross-linking patterns (a) showed that both NH2- and COOH-terminal fragments of TnI are accessible to both of the globular domains of TnC, (b) indicated that linkage of the NH2- and COOH-terminal sequences to the inhibitory region of TnI (TnIir) caused marked enhancement of cross-linking with native TnC and all seven thiol mutants, and (c) identified the region in TnC where TnIir binds as that containing residues 98, 133, 158, and 57. Thus, the results suggest that TnI and TnC may adopt flexible and dynamic conformations in which multiple interactions involving various domains of the two polypeptides occur and TnIir acting as a linker facilitates these interactions. The interaction of TnI and its fragments with actin, TnC, and TnT, considered together with the biological activity indicates that residues 96-120 represent a key structural and functional region of TnI. Whereas the NH2-terminal region of TnI stabilizes binding to TnC and TnT, the COOH-terminal region stabilizes TnC and actin binding.

Assignment of the human fast skeletal troponin T gene (TNNT3) to chromosome 11p15.5: evidence for the presence of 11pter in a monochromosome 9 somatic cell hybrid in NIGMS mapping panel 2

Human fast skeletal troponin T (TnTf), the tropomyosin binding component of the multisubunit troponin complex, plays an important role in the Ca2+ regulation of striated muscle contraction. Specific primers designed from the 3' end of human TnTf cDNA were used to amplify an intronic region by polymerase chain reaction (PCR). This TnTf-specific PCR product was detected from two somatic cell hybrids containing human chromosomes 9 and 11, respectively, in NIGMS mapping panel 2. However, further studies with other somatic hybrid cell lines (Bios Laboratory) localized the TnTf gene (HGMW-approved symbol TNNT3) only to chromosome 11. This observation was further confirmed by fluorescence in situ hybridization with a 12-kb TnTf genomic probe generated by extended PCR, showing the sublocalization of the gene to band p15.5 on chromosome 11. This locus is of specific interest, as Beckwith-Wiedemann syndrome and various childhood and adult tumor-related abnormalities have been mapped to this region. The study also indicates the presence of an 11pter region in the NIGMS cell hybrid GM10611, which has previously been reported to contain only human chromosome 9.

Overproduction and rapid purification of human fast skeletal beta troponin T using Escherichia coli expression vectors: functional differences between the alpha and beta isoforms

Troponin T (TpnT), an essential component of the Ca(2+)-regulatory troponin complex, is involved in protein-protein interactions with other thin-filament proteins during muscle contraction in vertebrate striated muscle (VSM). The isoforms of TpnT are encoded by members of a multigene family which, by alternate splicing, produces a complex pattern of isoproteins in VSM. The functional domains of TpnT are only tentatively identified and structure-function analysis on this protein is limited due to the heterogeneity of the multiple isoforms. We reasoned that the overproduction and purification of a single TpnT species in Escherichia coli would provide an insight into these studies, besides being useful in crystallizing the protein. We cloned the human fast skeletal beta TpnT-encoding cDNA (beta TpnTf) in three expression vectors. Overexpression was achieved in an E. coli BL21 (DE3) lysogen using a T7 RNA polymerase promoter-based vector, pET17b. The unfused recombinant protein was purified by a simple and rapid procedure in a biologically active and immunoreactive form. This is the first successful synthesis of a complete beta TpnTf polypeptide from any species using an in vitro expression system. Purified human beta TpnTf, a predominant fetal form, was less Ca(2+)-sensitive and exhibited considerably reduced affinity for troponin C and tropomyosin, as compared to the rabbit fast skeletal alpha TpnT, a predominant adult isoform. These results provide a biochemical correlate to the age-related differences in Ca2+ sensitivity of tension development in vertebrate fast skeletal muscles.

Overexpression and rapid purification of rabbit fast skeletal troponin I from Escherichia coli: effect of different promoters, host strains, and culture conditions

Rabbit fast skeletal troponin I (TnIf) cDNA was expressed using two Escherichia coli expression vectors, pRE1 containing the bacteriophage lambda pL promoter and pAED4, a T7 RNA polymerase-based vector. Although both vectors expressed TnIf, overexpression of the target protein was achieved with pAED4. The effect of several parameters such as culture condition, compatible host strain, and inhibition of protein synthesis by rifampicin on the expression of TnIf was investigated. The overexpressed target protein synthesized during a brief induction period of only 2 h was conveniently purified from inclusion bodies by a simple and rapid procedure involving extraction with urea, ultracentrifugation, DE-52 column chromatography, and gel filtration. About 50-75 mg of highly purified TnIf was obtained per liter E. coli culture by this method, which does not involve time-consuming multistep procedures such as affinity and ion exchange chromatography as previously reported in the literature. The isolated unfused protein is stable and is indistinguishable from native protein in all biological parameters examined. The parameters optimized in this report for overexpression of TnIf may also be applicable for other eukaryotic proteins.

Evaluation of psoralen with solar ultraviolet light (puvasol) and adjunctive topical tar therapy in psoriasis

Fifty patients having psoriasis were studied with a view to assess the efficacy of 'puvasol' (Oral psoralen with sun-rays exposure) alone and in combination with topical tar therapy and were placed in 2 groups, each group being consisted of 25 patients. At the end of 8 weeks, out of 25 patients (Group 1) receiving 'Puvasol' in combination with topital tar therapy 15 patients (60%) showed complete clearance, marked improvement of lesions were seen in 4 cases (16%) and deterioration in one case (4%). Out of 25 patients (Group I) receiving 'Puvasol' alone 8 cases (32%) showed complete clearance of lesions and 11 patients (44%) showed marked im-provement of lesions. It is found that topical tar therapy when used as an adjunct to 'Puvasol' was more effective than 'Puvasol' alone.

Isolation and characterization of human fast skeletal beta troponin T cDNA: comparative sequence analysis of isoforms and insight into the evolution of members of a multigene family

A cDNA encoding human fast skeletal beta troponin T (beta TnTf) has been isolated and characterized from a fetal skeletal muscle library. The cDNA insert is 1,000 bp in length and contains the entire coding region of 777 bp and 5' and 3' untranslated (UT) segments of 12 and 211 bp, respectively. The 3' UT segment shows the predicted stem-loop structure typical of eukaryotic mRNAs. The cDNA-derived amino acid sequence is the first available sequence for human beta TnTf protein. It is encoded by a single-copy gene that is expressed in a tissue-specific manner in fetal and adult fast skeletal muscles. Although the human beta TnTf represents the major fetal isoform, the sequence information indicates that this cDNA and the coded protein are quite distinct from the fetal and neonatal TnTf isoforms reported in other mammalian fetal muscles. The hydropathy plot indicates that human beta TnTf is highly hydrophilic along its entire length. The protein has an extremely high degree of predicted alpha-helical content involving the entire molecule except the carboxy-terminal 30 residues. Comparative sequence analysis reveals that the human beta TnTf shares a high level of sequence similarity in the coding region with other vertebrate TnTf and considerably reduced similarity with slow skeletal and cardiac TnT cDNAs. The TnT isoforms have a large central region consisting of amino acid residues 46-204 which shows a high sequence conservation both at the nucleotide and amino acid levels. This conserved region is flanked by the variable carboxy-terminal and an extremely variable amino-terminal segment. The tropomyosin-binding peptide of TnT, which is represented by amino acid residues 47-151 and also includes a part of troponin I binding region, is an important domain of this central segment. It is suggested that this conserved segment is encoded by an ancestral gene. The variable regions of vertebrate striated TnT isoforms reflect the subsequent addition and modification of genomic sequences to give rise to members of the TnT multigene family.

Beta-subunit of human chorionic gonadotropin hormone and firefly luciferase simultaneously synthesized in insect cells using a recombinant baculovirus are differentially expressed and transported

A recombinant baculovirus vAc beta hCG-luc was constructed that carried the cDNAs encoding firefly luciferase (luc) and beta-subunit of human chorionic gonadotropin (beta hCG) placed under the transcriptional control of individual copies of the baculovirus polyhedrin gene promoter. The simple, rapid, and sensitive detection of LUC expression was used for selecting recombinant viruses that simultaneously expressed beta hCG, which was identical in all respects to that synthesized using a recombinant baculovirus carrying the beta hCG gene alone. Immunofluorescence staining of virus-infected cells using anti-LUC antibodies revealed that LUC, a nonglycosylated, intracellular protein was retained within the cells whereas beta hCG, an extensively glycosylated, secretory protein, was processed and secreted into the culture medium. LUC and beta hCG were both immunoreactive on Western blot. beta hCG was bioactive, as evident from its ability to associate with alpha hCG and bind with the receptor and produce testosterone in an in vitro mouse Leydig cell assay system. Comparison of recombinant LUC and beta hCG synthesized by the virus-infected insect cells surprisingly revealed that the level of the former was quantitatively higher by at least 10-fold than the latter. A blot of total RNA isolated from vAc beta hCG-luc-infected insect cells, when probed with probes corresponding to the 3' region of the beta hCG or luc genes, indicated differential transcription of the two genes. Computer-aided sequence analysis indicated extensive secondary structure and stem-loop complex-forming potential of the beta hCG gene, which could be responsible for the transcriptional difference observed.

Antibodies to human papillomavirus and to other genital infectious agents and invasive cervical cancer risk

Human papillomaviruses (HPVs) play an important part in the development of cervical cancer, but the role of other infectious agents, such as herpes simplex virus (HSV), is not clear. We assayed serum samples collected from 219 women with cervical cancer and from 387 controls for antibody to infectious agents. HPV 16-E7 and/or HPV 18-E7 antibodies were significantly related to cervical cancer risk (RR 1.9, 95% CI 1.2-3.2). Antibodies to HSV types 1 and 2, Chlamydia trachomatis, and to multiple infectious agents were associated with cervical cancer when seroprevalence rates in all cases and controls were compared, but when HPV-seropositive cases and controls were compared these associations were weaker and non-significant. This finding suggests that past infections with sexually transmitted infections other than HPV may be surrogate markers of exposure to HPV, and of no separate aetiological significance.

Characterization of a rabbit fast skeletal troponin I cDNA: a comparative sequence analysis of vertebrate isoforms and tissue-specific expression of a single copy gene

A cDNA encoding skeletal fast troponin I (TnIf) has been isolated and characterized from an adult rabbit fast skeletal muscle cDNA library. This cDNA contains the entire coding region of 549 base pairs (bp), the 3' untranslated (UT) segment of 78 bp and the 5' UT segment of 74 bp. The 3' UT segment shows the predicted stem-loop structure characteristic of eukaryotic mRNAs. The cDNA-derived amino acid sequence is not identical to the chemically-derived and the recently reported cDNA-derived amino acid sequences for rabbit TnIf, and thus enables to make the necessary corrections in the sequence information. The rabbit TnIf is encoded by a single copy gene which is expressed in adult fast skeletal muscle in a tissue-specific manner. Comparative sequence analysis of the vertebrate TnI isoforms and their cDNAs shows a high level of sequence conservation in the coding region among the TnIf interspecies isoforms. The sequence similarity is markedly decreased among the fast, slow and cardiac intra- and inter-species isoforms. The C-terminal halves of TnI isoforms including a segment believed to be involved in critical interactions with actin and troponin C (TnC) show high sequence conservation whereas the N-terminal halves show considerable difference in sequence and size. The significance of these results in relation to the biological function and evolution of members of the vertebrate TnI multigene family is discussed.

Simultaneous synthesis of enzymatically active luciferase and biologically active beta subunit of human chorionic gonadotropin in caterpillars infected with a recombinant baculovirus

The beta subunit of human chorionic gonadotropin (beta hCG), a secretory and extensively glycosylated hormone, and firefly luciferase, a non-secretory enzyme, were simultaneously synthesized in Spodoptera larvae upon infection with a dual expression recombinant baculovirus, vAc beta hCG-luc. Luciferase was retained predominantly in the body tissue while beta hCG was secreted into the hemolymph of infected larvae. Both the proteins were similar to their authentic counterparts in terms of immunoreactivity and bioactivity. The caterpillar-derived recombinant hCG exhibited reduced electrophoretic mobility on SDS-PAGE and increased biological activity as compared to the hCG expressed in insect cells in culture. The implications of using the larval system for expressing an extensively glycosylated protein are discussed.

Neuritic leprosy: epidemiology and therapeutic responsiveness

We studied epidemiology, progression and therapeutic responsiveness in 62 cases of neuritic leprosy. Numbness was the main presenting symptom. Mononeuritis involving the ulnar nerve, followed by the common peroneal nerve was the commonest presentation. The lepromin test was positive in 34 cases while a slit-skin smear was negative in all cases. We treated 20 of these cases with dapsone monotherapy and 5 cases (25%) developed a skin lesion after an average duration of 3 months' treatment. We treated 42 cases with a combination of dapsone and rifampicin, and 3 cases (7%) developed a skin lesion after an average duration of 2-6 months. The subsequent diagnosis in cases developing skin lesions was borderline--lepromatous in 1 case, borderline-tuberculoid in 4 cases, tuberculoid in 2 cases and indeterminate in 1 case.

Indeterminate leprosy: a therapeutic evaluation

Out of 50 cases of indeterminate leprosy, 46 were male and 4 were female. The only clinical finding was a single hypopigmented macule in 38 (76%) cases. Nine (18%) patients had two and three (6%) cases had three hypopigmented macules. All patients were treated with multidrug therapy for one year. At the end of six months, the lesions were still active in 12 (24%) cases. At the end of one year of treatment it was found that 33 (66%) patients became inactive and 3 (6%) cases were still to be active. The study shows that all indeterminate leprosy cases must be treated with multidrug therapy till all signs of activity are subsided.

Localized borderline lepromatous leprosy

A 48-year-old soldier presented with 3 small leprosy lesions localized over the flexor area of the forearm. There was no nerve thickening and clinically the lesions looked like borderline-tuberculoid leprosy. However, these lesions demonstrated a bacteriological index (BI) of 4+ while no acid-fast bacilli (AFB) could be demonstrated from any other site of the body. A lepromin test was negative. Histologically evidence of borderline lepromatous leprosy was conspicuous. The case was diagnosed as localized borderline lepromatous-leprosy and treated with multidrug therapy. After 1 year of treatment, the lesions regressed, a lepromin test was positive (5 mm) and the BI from the lesions fell to 1+.

Firefly luciferase, synthesized to very high levels in caterpillars infected with a recombinant baculovirus, can also be used as an efficient reporter enzyme in vivo

Trichoplusia ni and Spodoptera littoralis larvae were infected with a recombinant AcNPV, having the viral polyhedrin gene replaced with the cDNA encoding firefly luciferase. Both S. littoralis and T. ni synthesized very high levels of luciferase representing greater than or equal to 25% and greater than or equal to 15%, respectively of the total Coomassie blue stainable protein. Luciferase was apparently not secreted into the hemolymph but was contained within the body tissue. Expression in S. littoralis larvae suggests that luciferase can be an excellent reporter enzyme to study virus infection, dissemination and expression in different tissues, host range determination, insect physiology and also to monitor the release of recombinant virus in the environment when used as a biocide.

Multidrug Regimen in Paucibacillary Leprosy For Six and Twelve Months (A Comapritive Study)

Efficacy of multidrug therapy (MDT) for paucibacillary leprosy for 12 months was evaluated in 91 fresh cases, which included indeterminate (28 cases), tuberculoid (22) and borderline tuberculoid leprosy (41 cases). All were males and were hospitawd. The MDT consisted of rifampicin 600 mg once a month and dapsone 100 mg daily. Both drugs were given concomitantly for 12 months. At the end of 6 months, 37.2% cases remained clinically active. At the end of once year, 91.2% cases receiving MDT became inactive.

A clinico-pathological study of multidrug regimen in paucibacillary leprosy

Preliminary results of a clinical trial in one hundred untreated paucibacillary leprosy cases with multidrug therapy (MDT) as per WHO recommendation are presented. Out of 100 fresh cases studied 18 had indeterminate, 35 tuberculoid and 47 cases had borderline tuberculoid leprosy. All were given MDT consisting of rifampicin 600 mg once a month and dapsone 100 mg daily for six months. At the end of six months all the cases were evaluated clinically and histopathological examination of lesions were studied. The lesions were still active in 35% of patient clinically and 47% histologically. Complete histological resolution have come across only in 4 cases suffering from indeterminate leprosy. Altogether 65% cases receiving MDT have shown marked improvement to total inactivation. Histologically, lymphocytic infiltration still persisted in 90% of slides examined and nerve infiltration were still present in 64% of cases at the end of six months receiving MDT.