Modification of acidic residues normalizes sodium dodecyl sulfate-polyacrylamide gel electrophoresis of caldesmon and other proteins that migrate anomalously

Flp/FRT-mediated disruption of ptex150 and exp2 in Plasmodium falciparum sporozoites inhibits liver-stage development

Plasmodium falciparum causes severe malaria and assembles a protein translocon (PTEX) complex at the parasitophorous vacuole membrane (PVM) of infected erythrocytes, through which several hundred proteins are exported to facilitate growth. The preceding liver stage of infection involves growth in a hepatocyte-derived PVM; however, the importance of protein export during P. falciparum liver infection remains unexplored. Here, we use the FlpL/FRT system to conditionally excise genes in P. falciparum sporozoites for functional liver-stage studies. Disruption of PTEX members ptex150 and exp2 did not affect sporozoite development in mosquitoes or infectivity for hepatocytes but attenuated liver-stage growth in humanized mice. While PTEX150 deficiency reduced fitness on day 6 postinfection by 40%, EXP2 deficiency caused 100% loss of liver parasites, demonstrating that PTEX components are required for growth in hepatocytes to differing degrees. To characterize PTEX loss-of-function mutations, we localized four liver-stage Plasmodium export element (PEXEL) proteins. P. falciparum liver specific protein 2 (LISP2), liver-stage antigen 3 (LSA3), circumsporozoite protein (CSP), and a Plasmodium berghei LISP2 reporter all localized to the periphery of P. falciparum liver stages but were not exported beyond the PVM. Expression of LISP2 and CSP but not LSA3 was reduced in ptex150-FRT and exp2-FRT liver stages, suggesting that expression of some PEXEL proteins is affected directly or indirectly by PTEX disruption. These results show that PTEX150 and EXP2 are important for P. falciparum development in hepatocytes and emphasize the emerging complexity of PEXEL protein trafficking.

Construction and Functionalization of a Clathrin Assembly for a Targeted Protein Delivery

Protein assemblies have drawn much attention as platforms for biomedical applications, including gene/drug delivery and vaccine, due to biocompatibility and functional diversity. Here, the construction and functionalization of a protein assembly composed of human clathrin heavy chain and light chain for a targeted protein delivery, is presented. The clathrin heavy and light chains are redesigned and associated with each other, and the resulting triskelion unit further self-assembled into a clathrin assembly with the size of about 28 nm in diameter. The clathrin assembly is dual-functionalized with a protein cargo and a targeting moiety using two different orthogonal protein-ligand pairs through one-pot reaction. The functionalized clathrin assembly exhibits about a 900-fold decreased K_D value for a cell-surface target due to avidity compared to a native targeting moiety. The utility of the clathrin assembly is demonstrated by an efficient delivery of a protein cargo into tumor cells in a target-specific manner, resulting in a strong cytotoxic effect. The present approach can be used in the creation of protein assemblies with multimodality.

Characterization of M116.1p, a murine cytomegalovirus protein required for efficient infection of mononuclear phagocytes

Broad tissue tropism of cytomegaloviruses (CMVs) is facilitated by different glycoprotein entry complexes, which are conserved between human CMV (HCMV) and murine CMV (MCMV). Among the wide array of cell types susceptible to the infection, mononuclear phagocytes (MNPs) play a unique role in the pathogenesis of the infection as they contribute both to the virus spread and immune control. CMVs have dedicated numerous genes for the efficient infection and evasion of macrophages and dendritic cells. In this study, we have characterized the properties and function of M116, a previously poorly described but highly transcribed MCMV gene region which encodes M116.1p, a novel protein necessary for the efficient infection of MNPs and viral spread in vivo. Our study further revealed that M116.1p shares similarities with its positional homologs in HCMV and RCMV, UL116 and R116, respectively, such as late kinetics of expression, N-glycosylation, localization to the virion assembly compartment, and interaction with gH - a member of the CMVs fusion complex. This study, therefore, expands our knowledge about virally encoded glycoproteins that play important roles in viral infectivity and tropism. Importance Human cytomegalovirus (HCMV) is a species-specific herpesvirus that causes severe disease in immunocompromised individuals and immunologically immature neonates. Murine cytomegalovirus (MCMV) is biologically similar to HCMV, and it serves as a widely used model for studying the infection, pathogenesis, and immune responses to HCMV. In our previous work, we have identified the M116 ORF as one of the most extensively transcribed regions of the MCMV genome without an assigned function. This study shows that the M116 locus codes for a novel protein, M116.1p, which shares similarities with UL116 and R116 in HCMV and RCMV, respectively, and is required for the efficient infection of mononuclear phagocytes and virus spread in vivo. Furthermore, this study establishes the α-M116 monoclonal antibody and MCMV mutants lacking M116, generated in this work, as valuable tools for studying the role of macrophages and dendritic cells in limiting CMV infection following different MCMV administration routes.

Identification and characterization of a Babesia bigemina thrombospondin-related superfamily member, TRAP-1: a novel antigen containing neutralizing epitopes involved in merozoite invasion

Background

Thrombospondin-related anonymous protein (TRAP) has been described as a potential vaccine candidate for several diseases caused by apicomplexan parasites. However, this protein and members of this family have not yet been characterized in Babesia bigemina, one of the most prevalent species causing bovine babesiosis.

Methods

The 3186-bp Babesia bigemina TRAP-1 (BbiTRAP-1) gene was identified by a bioinformatics search using the B. bovis TRAP-1 sequence. Members of the TRAP and TRAP-related protein families (TRP) were identified in Babesia and Theileria through a search of the TSP-1 adhesive domain, which is the hallmark motif in both proteins. Structural modeling and phylogenetic analysis were performed with the identified TRAP proteins. A truncated recombinant BbiTRAP-1 that migrates at approximately 107 kDa and specific antisera were produced and used in Western blot analysis and indirect fluorescent antibody tests (IFAT). B-cell epitopes with neutralizing activity in BbiTRAP-1 were defined by enzyme-linked immunosorbent assays (ELISA) and invasion assays.

Results

Three members of the TRAP family of proteins were identified in B. bigemina (BbiTRAP-1 to -3). All are type 1 transmembrane proteins containing the von Willebrand factor A (vWFA), thrombospondin type 1 (TSP-1), and cytoplasmic C-terminus domains, as well as transmembrane regions. The BbiTRAP-1 predicted structure also contains a metal ion-dependent adhesion site for interaction with the host cell. The TRP family in Babesia and Theileria species contains the canonical TSP-1 domain but lacks the vWFA domain and together with TRAP define a novel gene superfamily. A variable number of tandem repeat units are present in BbiTRAP-1 and could be used for strain genotyping. Western blot and IFAT analysis confirmed the expression of BbiTRAP-1 by blood-stage parasites. Partial recognition by a panel of sera from B. bigemina-infected cattle in ELISAs using truncated BbiTRAP-1 suggests that this protein is not an immunodominant antigen. Additionally, bovine anti-recombinant BbiTRAP-1 antibodies were found to be capable of neutralizing merozoite invasion in vitro.

Conclusions

We have identified the TRAP and TRP gene families in several Babesia and Theileria species and characterized BbiTRAP-1 as a novel antigen of B. bigemina. The functional relevance and presence of neutralization-sensitive B-cell epitopes suggest that BbiTRAP-1 could be included in tests for future vaccine candidates against B. bigemina.

N-terminal fusion of the N-terminal domain of bacterial enzyme I facilitates recombinant expression and purification of the human RNA demethylases FTO and Alkbh5

Various fusion tags are commonly employed to increase the heterologous expression and solubility of aggregation-prone proteins within Escherichia coli. Herein, we present a protocol for efficient recombinant expression and purification of the human RNA demethylases Alkbh5 and FTO. Our method incorporates a novel fusion tag (the N-terminal domain of bacterial enzyme I, EIN) that dramatically increases the solubility of its fusion partner and is promptly removed upon digestion with a protease. The presented protocol allows for the production of mg amounts of Alkbh5 and FTO in 1L of both rich and minimal media. We developed a liquid chromatography-mass spectrometry (LC-MS)-based assay to confirm that both proteins are enzymatically active. Furthermore, the LC-MS method developed here is applicable to other members of the AlkB family of Fe(II)/α-ketoglutarate-dependent dioxygenases. The superior protein yield, afforded by our expression and purification method, will facilitate biochemical investigations into the biological function of the human RNA demethylases and endorse employment of EIN as a broadly applicable fusion tag for recombinant expression projects.

The flagellar protein Enkurin is required for mouse sperm motility and for transport through the female reproductive tract

Enkurin was identified initially in mouse sperm where it was suggested to act as an intracellular adaptor protein linking membrane calcium influx to intracellular signaling pathways. In order to examine the function of this protein, a targeted mutation was introduced into the mouse Enkurin gene. Males that were homozygous for this mutated allele were subfertile. This was associated with lower rates of sperm transport in the female reproductive tract, including reduced entry into the oviduct and slower migration to the site of fertilization in the distal oviduct, and with poor progressive motility in vitro. Flagella from wild-type animals exhibited symmetrical bending and progressive motility in culture medium, and demembranated flagella exhibited the "curlicue" response to Ca2+ in vitro. In contrast, flagella of mice homozygous for the mutated allele displayed only asymmetric bending, nonprogressive motility, and a loss of Ca2+-responsiveness following demembrantion. We propose that Enkurin is part of a flagellar Ca2+-sensor that regulates bending and that the motility defects following mutation of the locus are the proximate cause of subfertility.

The Cryptosporidium parvum gp60 glycoprotein expressed in the ciliate Tetrahymena thermophila is immunoreactive with sera of calves infected with Cryptosporidium oocysts

Cryptosporidium parvum is a protozoan parasite of the phylum Apicomplexa responsible for cryptosporidiosis in calves, a disease that causes significant diarrhea and impairs gain of body weight, generating important production losses. As to now, no effective drugs or vaccines are available for the treatment or prevention of bovine cryptosporidiosis. Several reports suggest that development of a vaccine to prevent cryptosporidiosis is feasible, but relatively few vaccine candidates have been characterized and tested. The most prominent C. parvum antigen is gp60, an O-glycosylated mucin-like protein tethered to the parasite membrane by a glycosylphosphatidylinositol (GPI) anchor. Gp60 has been shown to be involved in essential mechanisms for the survival of C. parvum, such as recognition, adhesion to, and invasion of host cells. This work was aimed at expressing gp60 in Tetrahymena thermophila, a ciliated protozoon with numerous advantages for the heterologous expression of eukaryotic proteins, as a first approach for the development of a recombinant vaccine for bovine cryptosporidiosis. T. thermophila-expressed gp60 localized to the protozoon cell surface and oral apparatus, and partitioned into the Triton X-114 detergent phase. This indicates that the protein entered the reticuloendothelial system of the ciliate, and suggests it contains a GPI-anchor. Homogenates of gp60-expressing T. thermophila cells were recognized by sera from calves naturally infected with C. parvum demonstrating their immunoreactivity. In summary, the heterologous expression of gp60, a C. parvum-encoded GPI-anchored protein, has been successfully demonstrated in the ciliate T. thermophila.

Identification of non-conserved residues essential for improving the hydrocarbon-producing activity of cyanobacterial aldehyde-deformylating oxygenase

BACKGROUND

Cyanobacteria produce hydrocarbons corresponding to diesel fuels by means of aldehyde-deformylating oxygenase (ADO). ADO catalyzes a difficult and unusual reaction in the conversion of aldehydes to hydrocarbons and has been widely used for biofuel production in metabolic engineering; however, its activity is low. A comparison of the amino acid sequences of highly active and less active ADOs will elucidate non-conserved residues that are essential for improving the hydrocarbon-producing activity of ADOs.

RESULTS

Here, we measured the activities of ADOs from 10 representative cyanobacterial strains by expressing each of them in Escherichia coli and quantifying the hydrocarbon yield and amount of soluble ADO. We demonstrated that the activity was highest for the ADO from Synechococcus elongatus PCC 7942 (7942ADO). In contrast, the ADO from Gloeobacter violaceus PCC 7421 (7421ADO) had low activity but yielded high amounts of soluble protein, resulting in a high production level of hydrocarbons. By introducing 37 single amino acid substitutions at the non-conserved residues of the less active ADO (7421ADO) to make its sequence more similar to that of the highly active ADO (7942ADO), we found 20 mutations that improved the activity of 7421ADO. In addition, 13 other mutations increased the amount of soluble ADO while maintaining more than 80% of wild-type activity. Correlation analysis showed a solubility-activity trade-off in ADO, in which activity was negatively correlated with solubility.

CONCLUSIONS

We succeeded in identifying non-conserved residues that are essential for improving ADO activity. Our results may be useful for generating combinatorial mutants of ADO that have both higher activity and higher amounts of the soluble protein in vivo, thereby producing higher yields of biohydrocarbons.

Expression of a novel versican variant in dorsal root ganglia from spared nerve injury rats

The size and modular structure of versican and its gene suggest the existence of multiple splice variants. We have identified, cloned, and sequenced a previously unknown exon located within the noncoding gene sequence downstream of exon 8. This exon, which we have named exon 8β, specifies two stop-codons. mRNAs of the versican gene with exon 8β are predicted to be constitutively degraded by nonsense-mediated RNA decay. Here, we tested the hypothesis that these transcripts become expressed in a model of neuropathic pain.

Cloning, characterization and paper pulp applications of a newly isolated DyP type peroxidase from Rhodococcus sp. T1

A newly identified ligninolytic Rhodococcus strain (Rhodococcus sp. T1) was isolated from forestry wastes (Trabzon/Turkey). The DyP type peroxidase of Rhodococcus sp. T1 (DyPT1) was cloned, characterized and paper treated for industrial applications. Molecular weight of the protein was about 38 kDa. The kinetic parameters were 0.94 mM and 1417.53 µmol/min/mg for Km and Vmax, respectively. The enzyme was active at the temperature range of 25-65 °C and optimum temperature was 35 °C, enzyme was stable up to 6 days at room temperature. Optimum pH of the DyPT1 was 4.0 and it was stable between pH 4.0-6.0 up to 8 days at room temperature. Effects of some metal ions, Hemin, and some chemical agents on DyPT1 were determined. Hemin has implemented protective effects on the stability and the activity of the enzyme in long time periods when added into growing medium. DyPT1 was applied to eucalyptus kraft pulp for analyzing the bleaching efficiency, physical and optical tests of the manufuctared paper were carried out. Application of lignin peroxidase to kraft pulp caused a decrease of 5.2 units for kappa number and an increase from 52.05 to 64.18% in the delignification rate.

CABCOCO1, a novel coiled-coil protein With calcium-binding activity, is localized in the sperm flagellum

The gene 1700040L02Rik (GenBank accession number NM_028491, NP_082767.1) was selected by in silico screening as candidate that encodes a calcium-binding protein in sperm from a database of predicted mouse cilia-related genes. The predicted amino acid sequence revealed the presence of coiled-coil domain at the C-terminus and a CLAMP motif containing a leucine zipper domain in the middle of the protein. Assessment of a recombinant version of this protein by Stains-all and ruthenium red staining and by direct measurement of terbium binding revealed its calcium-binding activities. We therefore named this protein CABCOCO1 for calcium-binding coiled-coil protein-1. Immunohistochemical analyses showed its localization in spermatogenic cells of mouse testis. CABCOCO1 was first observed in the cytoplasm of murine spermatocytes, concentrated around centrioles of spermatids and co-localized with the centrosomal protein pericentrin. During the stage when centrosome number is reduced, CABCOCO1 relocalized to the murine sperm flagellum. On the other hand, in porcine sperm, whose proximal centriole remains intact while the distal centriole degenerates during spermiogenesis, CABCOCO1 localized both in the basal body and the flagellum. These results suggested that CABCOCO1 is involved in the control of sperm flagellar movement. Mol. Reprod. Dev. 83: 912-926, 2016 © 2016 Wiley Periodicals, Inc.

Identification, localization, and functional analysis of the homologues of mouse CABS1 protein in porcine testis

Previously, we have identified a calcium-binding protein that is specifically expressed in spermatids and localized to the flagella of the mature sperm in mouse, so-called mCABS1. However, the physiological roles of CABS1 in the male reproductive system have not been fully elucidated yet. In the current study, we aimed to localize and clarify the role of CABS1 in porcine (pCABS1). We determined for the first time the full nucleotides sequence of pCABS1 mRNA. pCABS1 protein was detected on SDS-PAGE gel as two bands at 75 kDa and 70 kDa in adult porcine testis, whereas one band at 70 kDa in epididymal sperm. pCABS1 immunoreactivity in seminiferous tubules was detected in the elongated spermatids, and that in the epididymal sperm was found in the acrosome as well as flagellum. The immunoreactivity of pCABS1 in the acrosomai region disappeared during acrosome reaction. We also identified that pCABS1 has a transmembrane domain using computational prediction of the amino acids sequence. The treatment of porcine capacitated sperm with anti-pCABS1 antiserum significantly decreased acrosome reactions. These results suggest that pCABS1 plays an important role in controlling calcium ion signaling during the acrosome reaction.

Recombinant Intrinsically Disordered Proteins for NMR: Tips and Tricks

The growing recognition of the several roles that intrinsically disordered proteins play in biology places an increasing importance on protein sample availability to allow the characterization of their structural and dynamic properties. The sample preparation is therefore the limiting step to allow any biophysical method being able to characterize the properties of an intrinsically disordered protein and to clarify the links between these properties and the associated biological functions. An increasing array of tools has been recruited to help prepare and characterize the structural and dynamic properties of disordered proteins. This chapter describes their sample preparation, covering the most common drawbacks/barriers usually found working in the laboratory bench. We want this chapter to be the bedside book of any scientist interested in preparing intrinsically disordered protein samples for further biophysical analysis.

Tyrosine-phosphorylated Ehrlichia chaffeensis and Ehrlichia canis tandem repeat orthologs contain a major continuous cross-reactive antibody epitope in lysine-rich repeats

A small subset of major immunoreactive proteins have been identified in Ehrlichia chaffeensis and Ehrlichia canis, including three molecularly and immunologically characterized pairs of immunoreactive tandem repeat protein (TRP) orthologs with major continuous species-specific epitopes within acidic tandem repeats (TR) that stimulate strong antibody responses during infection. In this study, we identified a fourth major immunoreactive TR-containing ortholog pair and defined a major cross-reactive epitope in homologous nonidentical 24-amino-acid lysine-rich TRs. Antibodies from patients and dogs with ehrlichiosis reacted strongly with recombinant TR regions, and epitopes were mapped to the N-terminal TR region (18 amino acids) in E. chaffeensis and the complete TR (24 amino acids) in E. canis. Two less-dominant epitopes were mapped to adjacent glutamate/aspartate-rich and aspartate/tyrosine-rich regions in the acidic C terminus of E. canis TRP95 but not in E. chaffeensis TRP75. Major immunoreactive proteins in E. chaffeensis (75-kDa) and E. canis (95-kD) whole-cell lysates and supernatants were identified with TR-specific antibodies. Consistent with other ehrlichial TRPs, the TRPs identified in ehrlichial whole-cell lysates and the recombinant proteins migrated abnormally slow electrophoretically a characteristic that was demonstrated with the positively charged TR and negatively charged C-terminal domains. E. chaffeensis TRP75 and E. canis TRP95 were immunoprecipitated with anti-pTyr antibody, demonstrating that they are tyrosine phosphorylated during infection of the host cell.

Replacement gene therapy with a human RPGRIP1 sequence slows photoreceptor degeneration in a murine model of Leber congenital amaurosis

RPGR-interacting protein-1 (RPGRIP1) is localized in the photoreceptor-connecting cilium, where it anchors the RPGR (retinitis pigmentosa GTPase regulator) protein, and its function is essential for photoreceptor maintenance. Genetic defect in RPGRIP1 is a known cause of Leber congenital amaurosis (LCA), a severe, early-onset form of retinal degeneration. We evaluated the efficacy of replacement gene therapy in a murine model of LCA carrying a targeted disruption of RPGRIP1. The replacement construct, packaged in an adeno-associated virus serotype 8 (AAV8) vector, used a rhodopsin kinase gene promoter to drive RPGRIP1 expression. Both promoter and transgene were of human origin. After subretinal delivery of the replacement gene in the mutant mice, human RPGRIP1 was expressed specifically in photoreceptors, localized correctly in the connecting cilia, and restored the normal localization of RPGR. Electroretinogram and histological examinations showed better preservation of rod and cone photoreceptor function and improved photoreceptor survival in the treated eyes. This study demonstrates the efficacy of human gene replacement therapy and validates a gene therapy design for future clinical trials in patients afflicted with this condition. Our results also have therapeutic implications for other forms of retinal degenerations attributable to a ciliary defect.

Developmental expression of high molecular weight tropomyosin isoforms in Mesocestoides corti

Tropomyosins are a family of actin-binding proteins with diverse roles in actin filament function. One of the best characterized roles is the regulation of muscle contraction. Tropomyosin isoforms can be generated from different genes, and from alternative promoters and alternative splicing from the same gene. In this work, we have isolated sequences for tropomyosin isoforms from the cestode Mesocestoides corti, and searched for tropomyosin genes and isoforms in other flatworms. Two genes are conserved in the cestodes M. corti and Echinococcus multilocularis, and in the trematode Schistosoma mansoni. Both genes have the same structure, and each gene gives rise to at least two different isoforms, a high molecular weight (HMW) and a low molecular weight (LMW) one. Because most exons are duplicated and spliced in a mutually exclusive fashion, isoforms from one gene only share one exon and are highly divergent. The gene duplication preceded the divergence of neodermatans and the planarian Schmidtea mediterranea. Further duplications occurred in Schmidtea, coupled to the selective loss of duplicated exons, resulting in genes that only code for HMW or LMW isoforms. A polyclonal antibody raised against a HMW tropomyosin from Echinococcus granulosus was demonstrated to specifically recognize HMW tropomyosin isoforms of M. corti, and used to study their expression during segmentation. HMW tropomyosins are expressed in muscle layers, with very low or absent levels in other tissues. No expression of HMW tropomyosins is present in early or late genital primordia, and expression only begins once muscle fibers develop in the genital ducts. Therefore, HMW tropomyosins are markers for the development of muscles during the final differentiation of genital primordia.

Identification of four Entamoeba histolytica organellar DNA polymerases of the family B and cellular localization of the Ehodp1 gene and EhODP1 protein

We report the identification of a family of four active genes (Ehodp1, Ehodp2, Ehodp3, and Ehodp4) encoding putative DNA polymerases in Entamoeba histolytica, the protozoan parasite responsible of human amoebiasis. The four Ehodp genes show similarity to DNA polymerases encoded in fungi and plant mitochondrial plasmids. EhODP polypeptides conserve the 3′-5′ exonuclease II and 5′-3′ polymerization domains, and they have the I, II, and III conserved boxes that characterize them as DNA polymerases of family B. Furthermore, we found in EhODP polymerases two novel A and B boxes, present also in DNA polymerases encoded in fungi mitochondrial plasmids. By in situ PCR, Ehodp1 gene was located in nuclei and in DNA-containing cytoplasmic structures. Additionally, using polyclonal antibodies against a recombinant rEhODP1-168 polypeptide, and confocal microscopy, EhODP1 was located in cytoplasmic DNA-containing structures.

Mass spectrometric analysis of Ehrlichia chaffeensis tandem repeat proteins reveals evidence of phosphorylation and absence of glycosylation

BACKGROUND

Ehrlichia chaffeensis has a small subset of immunoreactive secreted, acidic (pI approximately 4), tandem repeat (TR)-containing proteins (TRPs), which exhibit abnormally large electrophoretic masses that have been associated with glycosylation of the TR domain.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we examined the extent and nature of posttranslational modifications on the native TRP47 and TRP32 using mass spectrometry. Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) demonstrated that the mass of native TRP47 (33,104.5 Da) and TRP32 (22,736.8 Da) were slightly larger (179- and 288-Da, respectively) than their predicted masses. The anomalous migration of native and recombinant TRP47, and the recombinant TR domain (C-terminal region) were normalized by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) modification of negatively charged carboxylates to neutral amides. Exhaustive tandem mass spectrometric analysis (92% coverage) performed on trypsin and Asp-N digested native TRP47 identified peptides consistent with their predicted masses. Two TRP47 peptides not identified were located in the normally migrating amino (N)-terminal region of TRP47 and contained predicted phosphorylation sites (tyrosine and serine residues). Moreover, native TRP47 was immunoprecipitated from E. chaffeensis-infected cell lysate with anti-phosphotyrosine (anti-pTyr) antibody.

CONCLUSIONS/SIGNIFICANCE

TRP47 and TRP32 are not modified by glycans and the substantial net negative charge of the ehrlichial TRPs, and particularly the highly acidic TRs present within the ehrlichial TRPs, is responsible for larger-than-predicted masses. Furthermore, this study provides evidence that the N-terminal region of the TRP47 is tyrosine phosphorylated.

The acidic domains of the Toc159 chloroplast preprotein receptor family are intrinsically disordered protein domains

Background

The Toc159 family of proteins serve as receptors for chloroplast-destined preproteins. They directly bind to transit peptides, and exhibit preprotein substrate selectivity conferred by an unknown mechanism. The Toc159 receptors each include three domains: C-terminal membrane, central GTPase, and N-terminal acidic (A-) domains. Although the function(s) of the A-domain remains largely unknown, the amino acid sequences are most variable within these domains, suggesting they may contribute to the functional specificity of the receptors.

Results

The physicochemical properties of the A-domains are characteristic of intrinsically disordered proteins (IDPs). Using CD spectroscopy we show that the A-domains of two Arabidopsis Toc159 family members (atToc132 and atToc159) are disordered at physiological pH and temperature and undergo conformational changes at temperature and pH extremes that are characteristic of IDPs.

Conclusions

Identification of the A-domains as IDPs will be important for determining their precise function(s), and suggests a role in protein-protein interactions, which may explain how these proteins serve as receptors for such a wide variety of preprotein substrates.

Major species-specific antibody epitopes of the Ehrlichia chaffeensis p120 and E. canis p140 orthologs in surface-exposed tandem repeat regions

Ehrlichia chaffeensis and E. canis have a small subset of tandem repeat (TR)-containing protein orthologs, including p120/p140, which elicit strong antibody responses. The TR regions of these protein orthologs are immunoreactive, but the molecular characteristics of the p120/p140 epitopes have not been determined. In this study, the immunodeterminants of the E. chaffeensis p120 and E. canis p140 were identified and molecularly defined. Major antibody epitope-containing regions of both p120 and p140 were localized to the TR regions, which reacted strongly by Western immunoblotting with antibodies in sera from E. chaffeensis-infected dogs or patients and E. canis-infected dogs, respectively. Single continuous species-specific major epitopes within the E. chaffeensis p120 and E. canis p140 TRs were mapped to homologous surface-exposed glutamate/aspartate-rich regions (19 to 22 amino acids). In addition, minor cross-reactive epitopes were localized to homologous N- and C-terminal regions of p120 and p140. Furthermore, although the native and recombinant p120 and p140 proteins exhibited higher-than-predicted molecular masses, posttranslational modifications were not present on abnormally migrating p120 and p140 TR recombinant proteins as determined by matrix-assisted laser desorption ionization-time of flight mass spectrometry.

CABS1 is a novel calcium-binding protein specifically expressed in elongate spermatids of mice

Single intraperitoneal injection of busulfan at 20 mg/kg body weight to mature male mice induced the deletion of the spermatogenic cells, followed by the restoration of the spermatogenesis by the surviving undifferentiated spermatogonia. The changes of the protein contents in testis during these processes were analyzed by two-dimensional gel electrophoresis in order to identify the proteins expressed at the specific stages of spermatogenesis. An acidic protein that disappeared and recovered in the same time course as spermatids after the busulfan treatment was identified as CABS1 by mass spectrometry. It was found that CABS1 was specifically expressed in the elongate spermatids at steps 13 to 16 in stages I to VIII of the seminiferous epithelium cycle of the mouse, and then it localized to the principal piece of flagellum of the mature sperm in the cauda epididymis. We have found for the first time that CABS1 is a calcium-binding protein that binds calcium during the maturation in the epididymis.

An apicomplexan ankyrin-repeat histone deacetylase with relatives in photosynthetic eukaryotes

Cryptosporidium parvum is a member of the Apicomplexa that lacks a plastid and associated nuclear-encoded genes, which has hampered its use in evolutionary comparisons with algae and eliminated a pool of potentially useful drug targets. Here we show that apicomplexan parasites possess an unusual family of class II histone deacetylase (HDAC) proteins with orthologues that are present in other chromalveolates and primitive algae. A striking feature of these HDAC proteins is the presence of ankyrin repeats in the amino-terminus that appear to be required for enzyme activity. In vitro and in vivo analyses of the C. parvum orthologue indicate that this subclass of chromatin-remodelling proteins is targeted by the anti-cancer drug suberoylanilide hydroxamic acid and that these proteins are most likely involved in the essential process of H4 histone deacetylation that coincides with DNA replication. We propose that members of this novel class of histone deacetylase can serve as promising new targets for treatments against debilitating diseases such as cryptosporidosis, toxoplasmosis and malaria.

Diffusion of anionic and neutral GFP derivatives through plasmodesmata in epidermal cells of Nicotiana benthamiana

Plasmodesmata (Pd) are trans-wall membrane channels that permit cell-to-cell transport of metabolites and other small molecules, proteins, RNAs, and signaling molecules. The transport of cytoplasmic soluble macromolecules is a function of the electrochemical gradient between adjacent cells, the number of Pd per interface between adjacent cells, Stokes radius (R(S)), area of the cytoplasmic annulus, and channel length. The size of the largest molecule that can pass through Pd defines the Pd size exclusion limit. However, since the shape and size of a molecule determines its capacity to diffuse through pores or tubes, R(S) is a better measure. Relatively small changes in R(S) can cause large differences in the mobility of molecular probes, particularly if the pore size is close to that of the probe. In addition, as the dimensions of a macromolecule approach that of the channel, membrane charge effects may become important. We employed quantitative tools and molecular modeling to measure the apparent coefficient of conductivity of Pd, C(Pd), for the non-targeted transport of macromolecules. This method allowed us to examine the influence of protein charge and R(S) on C(Pd) in Nicotiana benthamiana. The C(Pd) of modified green fluorescent proteins (GFPs) of different sizes but with the same charge as native GFP and of a more negatively charged derivative were determined. We found that the C(Pd) of cytoplasmic soluble GFP and cytoplasmic forms of modified GFP were the most strongly correlated with R(S) and that the apparent aberrant increase in C(Pd) of a negatively charged GFP derivative was, at least in part, the result of the charge effect on R(S).

Characterization of white spot syndrome virus envelope protein VP51A and its interaction with viral tegument protein VP26

In this study, we characterize a novel white spot syndrome virus (WSSV) structural protein, VP51A (WSSV-TW open reading frame 294), identified from a previous mass spectrometry study. Temporal-transcription analysis showed that vp51A is expressed in the late stage of WSSV infection. Gene structure analysis showed that the transcription initiation site of vp51A was 135 bp upstream of the translation start codon. The poly(A) addition signal overlapped with the translation stop codon, TAA, and the poly(A) tail was 23 bp downstream of the TAA. Western blot analysis of viral protein fractions and immunoelectron microscopy both suggested that VP51A is a viral envelope protein. Western blotting of the total proteins extracted from WSSV virions detected a band that was close to the predicted 51-kDa mass, but the strongest signal was around 72 kDa. We concluded that this 72-kDa band was in fact the full-length VP51A protein. Membrane topology assays demonstrated that the VP51A 72-kDa protein is a type II transmembrane protein with a highly hydrophobic transmembrane domain on its N terminus and a C terminus that is exposed on the surface of the virion. Coimmunoprecipitation, colocalization, and yeast two-hybrid assays revealed that VP51A associated directly with VP26 and indirectly with VP28, with VP26 acting as a linker protein in the formation of a VP51A-VP26-VP28 complex.

A variable-length PCR target protein of Ehrlichia chaffeensis contains major species-specific antibody epitopes in acidic serine-rich tandem repeats

Ehrlichia chaffeensis and E. canis have a small subset of tandem repeat (TR)-containing proteins that elicit strong host immune responses and are associated with host-pathogen interactions. In a previous study, we molecularly characterized a highly conserved 19-kDa major immunoreactive protein (gp19) of E. canis and identified the corresponding TR-containing ortholog variable-length PCR target (VLPT) protein in E. chaffeensis. In this study, the native 32-kDa VLPT protein was identified and the immunodeterminants defined in order to further understand the molecular basis of the host immune response to E. chaffeensis. Synthetic and/or recombinant polypeptides corresponding to various regions of VLPT were used to localize major antibody epitopes to the TR-containing region. Major antibody epitopes were identified in three nonidentical repeats (R2, R3, and R4), which reacted strongly with antibodies in sera from an E. chaffeensis-infected dog and human monocytotropic ehrlichiosis patients. VLPT-R3 and VLPT-R2 reacted most strongly with antibody, and the epitope was further localized to a nearly identical proximal 17-amino-acid region common between these repeats that was species specific. The epitope in R4 was distinct from that of R2 and R3 and was found to have conformational dependence. VLPT was detected in supernatants from infected cells, indicating that the protein was secreted. VLPT was localized on both reticulate and dense-core cells, and it was found extracellularly in the morula fibrillar matrix and associated with the morula membrane.

Cloning, expression and immunogenicty analysis of five outer membrane proteins of Vibrio parahaemolyticus zj2003

Genes of five outer membrane proteins of Vibrio parahaemolyticus zj2003, including OmpW, OmpV, OmpK, OmpU and TolC, were cloned and expressed as N-terminal His(6)-tagged proteins in Escherichia coli. The recombinant fusion proteins were purified with nickel chelate affinity chromatography. To analyze the immunogenicity of these proteins, large yellow croaker (Pseudosciaena crocea) were immunized by intraperitoneal injection. Antibody response was assessed by method of enzyme-linked immunosorbent assay. Titres to all five recombinant proteins increased during 4 to 8 weeks post immunization, within the range of log 2 values of 5.75 to 10.8. Recorded relative survival percent (RPS) of the vaccinated groups varied from 80% to 90%, while 10 fish in control group all died. Western blot tests were undertaken with the serum of survival fish after experimental infection. Except for recombinant TolC, the other four recombinant proteins were recognized by the serum. It is indicated that four outer membrane proteins of V. parahaemolyticus zj2003, including OmpW, OmpV, OmpU and OmpK, are immunogenic during in vivo infection, which would be of some significance in developing efficient vaccine in aquaculture. This is the first report of successful vaccination against V. parahaemolyticus with purified recombinant outer membrane proteins.

Expression, purification and characterization of recombinant phospholipase B from Moraxella bovis with anomalous electrophoretic behavior

Moraxella bovis is the causative agent of infectious bovine keratoconjunctivitis (IBK) also known as pinkeye, a highly contagious and painful eye disease that is common in cattle throughout the world. Vaccination appears to be a reasonable and cost-effective means of control of pinkeye. Identification of genes encoding novel secreted antigens have been reported, and these antigens are being assessed for use in a vaccine. One of the genes encodes phospholipase B, which can be expressed with high purity and yield in recombinant Escherichia coli as a secreted, soluble, non-tagged, mature construct (less signal peptide with predicted mass 63 kDa). The recombinant phospholipase B exhibited anomalous electrophoretic mobility that was dependent on the temperature of the denaturing process, with bands observed at either 52 or 63 kDa. Analysis by in-gel digestion and liquid chromatography-mass spectrometry revealed these two distinct forms most likely had identical sequences. Phospholipase B is a compact, globular protein with a predicted structure typical of a conventional autotransporter. It is suggested that high temperature is required to unfold the protein (to denature the beta-barrel-rich transporter domain) and to ensure accessibility of the reducing agent. Interestingly, the two forms of the enzyme, differing in size and isoelectric points, were also detected in cell-free supernatants of M. bovis cultures, indicating that native phospholipase B may exist in two differentially folded states possibly also differing in oxidation status of cysteine residues.

Dimerization and DNA-binding properties of the transcription factor DeltaFosB

The transcription factor, DeltaFosB, a splice isoform of fosB, accumulates in rodents in a brain-region-specific manner in response to chronic administration of drugs of abuse, stress, certain antipsychotic or antidepressant medications, electroconvulsive seizures, and certain lesions. Increasing evidence supports a functional role of such DeltaFosB induction in animal models of several psychiatric and neurologic disorders. Fos family proteins, including DeltaFosB, are known to heterodimerize with Jun family proteins to create active AP-1 transcription-factor complexes, which bind to DNA specifically at AP-1 consensus sites. We show here, using a range of biochemical and biophysical means, that recombinant, purified DeltaFosB forms homodimers as well, at concentrations less than 500 nM, and that these homodimers specifically bind to DNA oligonucleotides containing AP-1 consensus sequences in the absence of any Jun partner. Our results suggest that, as DeltaFosB accumulates to abnormally elevated protein levels in highly specific regions of the brain in response to chronic stimulation, functional homodimers of DeltaFosB are formed with the potential to uniquely regulate patterns of gene expression and thereby contribute to the complex processes of neural and behavioral adaptation.

The acidity of protein fusion partners predominantly determines the efficacy to improve the solubility of the target proteins expressed in Escherichia coli

Maximization of the soluble protein expression in Escherichia coli (E. coli) via the fusion expression strategy is usually preferred for academic, industrial and pharmaceutical purposes. In this study, a set of distinct protein fusion partners were comparatively evaluated to promote the soluble expression of two target proteins including the bovine enterokinase largely prone to aggregation and the green fluorescent protein with moderate native solubility. Within protein attributes that are putatively involved in protein solubility, the protein acidity was of particular concern. Our results explicitly indicated the protein fusion partners with a stronger acidity remarkably exhibited a higher capacity to enhance the solubility of the target proteins. Among them, msyB, an E. coli acidic protein that suppresses the mutants lacking function of protein export, was revealed as an excellent protein fusion partner with the distinguished features including high potential to enhance protein solubility, efficient expression, relatively small size and the origin of E. coli itself. In principle, our results confirmed the modified solubility model of Wilkinson-Harrison and especially deepened understanding its essence. Meanwhile, the roles of other parameters such as protein hydrophilicity in solubility enhancement were discussed, a guideline to design or search an optimum protein solubility enhancer was also proposed.

Hamster contraception associated protein 1 (CAP1)

Based on cDNA and amino acid sequence, we demonstrate that hamster contraception associated protein 1 (CAP1) protein (an homolog of DJ-1 in mouse, CAP1/SP22/RS in rat and DJ-1/RS in human) is conserved during evolution. Through solubilization studies, it was demonstrated that hamster CAP1 has a peripheral membrane localization. SDS-PAGE analysis revealed that the migration pattern for hamster CAP1 compared to the other rodent counterparts, rat and mouse was different; indicating species-specific differences in the protein (possibly due to post-translational modifications). This protein also shows a ubiquitous presence in both somatic and germ tissues, and has been localized to the sperm tail. It was noticed that hamster CAP1 was lost from the mid piece of spermatozoa during capacitation. Interestingly, following in vitro treatment with ornidazole, CAP1 was lost from the spermatozoa and immunofluorescence studies showed that the major loss was from the mid piece of the spermatozoa. Another interesting feature highlighted about hamster CAP1 is its tendency to exist in two pI isoforms. Summarily, hamster CAP1 appears to exhibit species-specific differences compared to its rodent counterparts with respect to its unique peripheral localization, its size, two pI isoforms, and fate during capacitation, which may have implications in its functions.

The Anp32 family of proteins containing leucine-rich repeats

Herein we describe the characteristic features of the Anp32 family represented by the cerebellar leucine-rich repeat protein (Lanp) and the cerebellar developmental-regulated protein 1 (Cpd1). The Anp32 family consists of 32 evolutionarily-conserved proteins and is included within the superfamily of leucine-rich repeat (LRR) proteins characterized by the presence of tandem arrays of a LRR, a structural motif implicated in the mediation of protein-protein interactions. We describe three novel human Anp32 proteins, reveal the evolutionary relationships of the members of the Anp32 family, provide insights into their biochemical and structural properties, and review their macromolecular interactions, substrate specificities, tissue distribution/expression patterns, and physiological and pathological roles. Recent findings indicate a conserved role of members of the Anp32 family during evolution in the modulation of cell signalling and transduction of gene expression to regulate the morphology and dynamics of the cytoskeleton, cell adhesion, neural development or cerebellar morphogenesis.

Molecular and electrophysiological characterization of nucleotide-sensitive chloride current-inducing protein of Fasciola hepatica

Nucleotide-sensitive chloride current regulating proteins (ICln's) of the chloride channels have been characterized from man and animals. An ICln of Fasciola hepatica (ICln-Fh) consisting of 231 amino acids revealed high similarities to both consensus domain of ICln's and two acidic residue-abundant patches in its C-terminus. Native ICln-Fh protein was confirmed present in F. hepatica soluble extract by immunoblotting. The recombinant ICln-Fh protein expressed in collagenase-defolliculated Xenopus oocytes induced fast rising and outward rectifying Cl- currents (I(Cln-Fh)). The recombinant ICln-Fh protein, however, did not trigger cell swelling-induced Cl- currents (I(Cl-swell)). The I(Cln-Fh) currents were significantly reduced by substituting external Cl- with gluconic acid and by externally adding cAMP. Collectively, these results suggest that ICln-Fh protein is an inducer of Cl- currents in F. hepatica.

MARCKS is a natively unfolded protein with an inaccessible actin-binding site: evidence for long-range intramolecular interactions

Myristoylated alanine-rich C kinase substrate (MARCKS) is an unfolded protein that contains well characterized actin-binding sites within the phosphorylation site domain (PSD), yet paradoxically, we now find that intact MARCKS does not bind to actin. Intact MARCKS also does not bind as well to calmodulin as does the PSD alone. Myristoylation at the N terminus alters how calmodulin binds to MARCKS, implying that, despite its unfolded state, the distant N terminus influences binding events at the PSD. We show that the free PSD binds with site specificity to MARCKS, suggesting that long-range intramolecular interactions within MARCKS are also possible. Because of the unusual primary sequence of MARCKS with an overall isoelectric point of 4.2 yet a very basic PSD (overall charge of +13), we speculated that ionic interactions between oppositely charged domains of MARCKS were responsible for long-range interactions within MARCKS that sterically influence binding events at the PSD and that explain the observed differences between properties of the PSD and MARCKS. Consistent with this hypothesis, chemical modifications of MARCKS that neutralize negatively charged residues outside of the PSD allow the PSD to bind to actin and increase the affinity of MARCKS for calmodulin. Similarly, both myristoylation of MARCKS and cleavage of MARCKS by calpain are shown to increase the availability of the PSD so as to activate its actin-binding activity. Because abundant evidence supports the conclusion that MARCKS is an important protein in regulating actin dynamics, our data imply that post-translational modifications of MARCKS are necessary and sufficient to regulate actin-binding activity.

Leishmania major elongation factor 1B complex has trypanothione S-transferase and peroxidase activity

In the Trypanosomatidae, trypanothione has subsumed many of the roles of glutathione in defense against chemical and oxidant stress. Crithidia fasciculata lacks glutathione S-transferase, but contains an unusual trypanothione S-transferase activity that is associated with eukaryotic translation elongation factor 1B (eEF1B). Here we describe the cloning, expression, and reconstitution of the purified alpha, beta, and gamma subunits of eEF1B from Leishmania major. Individual subunits lacked trypanothione S-transferase activity. Only eEF1B, formed by reconstitution or co-expression of the three subunits, was able to conjugate a variety of electrophilic substrates to trypanothione or glutathionylspermidine, but not glutathione. In contrast to the C. fasciculata eEF1B, the L. major enzyme also displayed peroxidase activity against a variety of organic hydroperoxides. The enzyme showed no activity with hydrogen peroxide and greatest activity with linoleic acid hydroperoxide (1 unit mg(-1)). Kinetic studies suggest a ternary complex mechanism, with Km values of 140 mum for trypanothione and 7.4 mm for cumene hydroperoxide and kcat=25 s(-1). Immunofluorescence studies indicate that the enzyme may be localized to the surface of the endoplasmic reticulum. These results suggest that, in addition to its role in protein synthesis, the Leishmania eEF1B may help protect the parasite from lipid peroxidation.

Trypanothione S-transferase activity in a trypanosomatid ribosomal elongation factor 1B

Trypanothione is a thiol unique to the Kinetoplastida and has been shown to be a vital component of their antioxidant defenses. However, little is known as to the role of trypanothione in xenobiotic metabolism. A trypanothione S-transferase activity was detected in extracts of Leishmania major, L. infantum, L. tarentolae, Trypanosoma brucei, and Crithidia fasciculata, but not Trypanosoma cruzi. No glutathione S-transferase activity was detected in any of these parasites. Trypanothione S-transferase was purified from C. fasciculata and shown to be a hexadecameric complex of three subunits with a relative molecular weight of 650,000. This enzyme complex was specific for the thiols trypanothione and glutathionylspermidine and only used 1-chloro-2,4-dinitrobenzene from a range of glutathione S-transferase substrates. Peptide sequencing revealed that the three components were the alpha, beta, and gamma subunits of ribosomal eukaryotic elongation factor 1B (eEF1B). Partial dissociation of the complex suggested that the S-transferase activity was associated with the gamma subunit. Moreover, Cibacron blue was found to be a tight binding inhibitor and reactive blue 4 an irreversible time-dependent inhibitor that covalently modified only the gamma subunit. The rate of inactivation by reactive blue 4 was increased more than 600-fold in the presence of trypanothione, and Cibacron blue protected the enzyme from inactivation by 1-chloro-2,4-dinitrobenzene, confirming that these dyes interact with the active site region. Two eEF1Bgamma genes were cloned from C. fasciculata, but recombinant C. fasciculata eEF1Bgamma had no S-transferase activity, suggesting that eEF1Bgamma is unstable in the absence of the other subunits.

Biophysical characterization of Gir2, a highly acidic protein of Saccharomyces cerevisiae with anomalous electrophoretic behavior

Gir2 is an uncharacterized protein of Saccharomyces cerevisiae, containing a RWD/GI domain. In this work, we report the biophysical characterization of Gir2. His-tagged Gir2, expressed and purified from Escherichia coli, showed an abnormally slow migration on SDS-PAGE. The yeast expressed protein behaves similarly. Using mass spectrometry and peptide mass fingerprinting we demonstrated that the protein has the expected molecular mass (34kDa). EDC modification of carboxylate groups reverted the anomalous migration on SDS-PAGE. Size exclusion chromatography showed that Gir2 has a Stokes radius larger than expected. Gir2 is thermostable and lacks extensive structure, as determined by CD analysis. Based on these findings, we suggest that Gir2 is a representative of the growing group of "natively unfolded" proteins.

Induced folding of the U2AF35 RRM upon binding to U2AF65

The human essential splicing factor U2AF (U2 auxiliary factor) consists of 35 and 65 kDa subunits which form a highly stable heterodimer in solution. Copurification of the recombinant U2AF35 RNA recognition motif (U2AF35 RRM) and full-length U2AF65 yields a soluble and functionally active minimal U2AF heterodimer. Recombinant U2AF35 RRM protein free and in complex with three different regions of U2AF65 was characterized by nuclear magnetic resonance spectroscopy. We found that the recombinant U2AF35 RRM is unstructured in solution but its tertiary structure is induced upon binding to U2AF65. This interaction is mediated by the N-terminal proline-rich region of U2AF65 and does not involve the U2AF65 RRMs.

A short segment of the R domain of cystic fibrosis transmembrane conductance regulator contains channel stimulatory and inhibitory activities that are separable by sequence modification

The regulatory (R) domain of the cystic fibrosis transmembrane conductance regulator (CFTR) contains consensus phosphorylation sites for cAMP-dependent protein kinase (PKA) that are the basis for physiological regulation of the CFTR chloride channel. A short peptide segment in the R domain with a net negative charge of B9 (amino acids 817-838, NEG2) and predicted helical tendency is shown to play a critical role in CFTR chloride channel function. Deletion of NEG2 from CFTR completely eliminates the PKA dependence of channel activity. Exogenous NEG2 peptide interacts with CFTR to exert both stimulatory and inhibitory effects on the channel function. The NEG2 peptide with sequence scrambled to remove helical tendencies also inhibits channel function, but does not stimulate. Similar results are found for a NEG2 peptide whose helical structure is disrupted by a proline residue. When six of the negatively charged carboxylic acid residues are replaced by their cognate amides, reducing net negative charge to B3, but increasing helical propensity as assessed by circular dichroism, the peptide stimulates CFTR channel function, but does not inhibit. We speculate that the NEG2 region interacts with other cytosolic domains of CFTR to control opening and closing transitions of the chloride channel.

The 65 and 110 kDa SR-related proteins of the U4/U6.U5 tri-snRNP are essential for the assembly of mature spliceosomes

The association of the U4/U6.U5 tri-snRNP with pre-spliceosomes is a poorly understood step in the spliceosome assembly pathway. We have identified two human tri-snRNP proteins (of 65 and 110 kDa) that play an essential role in this process. Characterization by cDNA cloning of the 65 and 110 kDa proteins revealed that they are likely orthologues of the yeast spliceosomal proteins Sad1p and Snu66p, respectively. Immunodepletion of either protein from the HeLa cell nuclear extracts inhibited pre-mRNA splicing due to a block in the formation of mature spliceosomes, but had no effect on the integrity of the U4/U6.U5 tri-snRNP. Spliceosome assembly and splicing catalysis could be restored to the respective depleted extract by the addition of recombinant 65 or 110 kDa protein. Our data demonstrate that both proteins are essential for the recruitment of the tri-snRNP to the pre-spliceosome but not for the maintenance of the tri-snRNP stability. Moreover, since both proteins contain an N-terminal RS domain, they could mediate the association of the tri-snRNP with pre-spliceosomes by interaction with members of the SR protein family.

Caldesmon reduces the apparent rate of binding of myosin S1 to actin-tropomyosin

Equilibrium measurements of the rate of binding of caldesmon and myosin S1 to actin-tropomyosin from different laboratories have yielded different results and have led to different models of caldesmon function. An alternate approach to answering these questions is to study the kinetics of binding of both caldesmon and S1 to actin. We observed that caldesmon decreased the rate of binding of S1 to actin in a concentration-dependent manner. The inhibition of the rate of S1 binding was enhanced by tropomyosin, but the effect of tropomyosin on the binding was small. Premixing actin with S1 reduced the amplitude (extent) of caldesmon binding in proportion to the fraction of actin that contained bound S1, but the rate of binding of caldesmon to free sites was not greatly altered. No evidence for a stable caldesmon-actin-tropomyosin-S1 complex was observed, although S1 did apparently bind to gaps between caldesmon molecules. These results indicate that experiments involving caldesmon, actin, tropomyosin, and myosin are inherently complex. When the concentration of either S1 or caldesmon is varied, the amount of the other component bound to actin-tropomyosin cannot be assumed to remain fixed. The results are not readily explained by a mechanism in which caldesmon acts only by stabilizing an inactive state of actin-tropomyosin. The results support regulatory mechanisms that involve changes in the actin-S1 interaction.

Abnormal thiol reactivity of tropomyosin in essential hypertension and its association with abnormal sodium-lithium countertransport kinetics

OBJECTIVES

To identify a thiol protein that is abnormal in a subgroup of essential hypertensive (EHT) patients who have a strong family history of hypertension and cardiovascular disease and have a low Km of erythrocyte Na/Li countertransport (CT).

METHODS

To detect biotin maleimide labelling of a key thiol protein to investigate its reaction with N-ethylmaleimide (NEM) in normal and EHT erythrocytes.

RESULTS

The thiol protein of 33 kDa apparent molecular weight (p33) identified by the loss of labelling with biotin maleimide was identified as tropomyosin due to its retarded running in 6 mol/l urea gels and immunoblotting. The NEM reaction with p33 detected by loss of subsequent biotin maleimide labelling is biphasic in normal control erythrocytes with the rate in the first 30 s double that after 30 s. In EHT erythrocytes NEM reaction (1) after 30 s is faster than normal and (2) in the first 30 s causes a paradoxical increase in apparent biotin maleimide labelling. In normal control erythrocytes, the loss of biotin maleimide labelling with NEM reaction or the faster phenylmaleimide reaction follows the same time course as the decrease in Km of Na/Li CT.

CONCLUSIONS

NEM reaction with p33 requires two thiols. Only the cytoskeletal form of tropomyosin from the TM3 gene has more than one thiol group and agrees with SDS-PAGE mobility. Tropomyosin is a strong candidate to explain the familial abnormality in EHT with abnormal Na/ Li CT and it could explain many of the characteristics of this disease.

Replacement of Lys-75 of calmodulin affects its interaction with smooth muscle caldesmon

The interaction of smooth muscle caldesmon with synthetic calmodulin (SynCam) and its five mutants with replacement of Lys-75 was analyzed by means of intrinsic Trp fluorescence, zero-length crosslinking and by caldesmon-induced inhibition of actomyosin ATPase activity. SynCam and its double mutant with replacement K75P and simultaneous insertion of KGK between residues 80 and 81 have a comparably low affinity to caldesmon and the probability of crosslinking of this mutant to caldesmon was the lowest among all mutants analyzed. SynCam and its double mutant (K75P+KGK) induced nearly complete reversion of caldesmon inhibition of actomyosin ATPase activity with half-maximal reversion achieved at about 1 microM. Two mutants, K75A and K75V, with partially stabilized less positive central domain have higher affinity to caldesmon. These mutants induce 80-85% reversion of caldesmon inhibition of actomyosin ATPase and the half-maximal reversion was achieved at about 0.3-0.4 microM. Two last mutants, K75P and K75E, with distorted central domain have high affinity to caldesmon and the probability of crosslinking of K75P to caldesmon was the highest among calmodulin mutants tested. These mutants induced complete reversion of caldesmon inhibition with half-maximal effect observed at 0.3-0.4 microM. We suggest that the length, flexibility and charge of the central domain affect binding of calmodulin mutants and their ability to reverse caldesmon-induced inhibition of actomyosin ATPase activity.

Human Upf proteins target an mRNA for nonsense-mediated decay when bound downstream of a termination codon

Nonsense-mediated decay (NMD) rids eukaryotic cells of aberrant mRNAs containing premature termination codons. These are discriminated from true termination codons by downstream cis-elements, such as exon-exon junctions. We describe three novel human proteins involved in NMD, hUpf2, hUpf3a, and hUpf3b. While in HeLa cell extracts these proteins are complexed with hUpf1, in intact cells hUpf3a and hUpf3b are nucleocytoplasmic shuttling proteins, hUpf2 is perinuclear, and hUpf1 cytoplasmic. hUpf3a and hUpf3b associate selectively with spliced beta-globin mRNA in vivo, and tethering of any hUpf protein to the 3'UTR of beta-globin mRNA elicits NMD. These data suggest that assembly of a dynamic hUpf complex initiates in the nucleus at mRNA exon-exon junctions and triggers NMD in the cytoplasm when recognized downstream of a translation termination site.

Expression of a foreign epitope by porcine reproductive and respiratory syndrome virus

The potential of porcine reproductive and respiratory syndrome virus (PRRSV) as a viral vector was explored by the insertion of a sequence encoding a foreign antigen into the infectious cDNA clone of the Lelystad virus isolate. An epitope of the hemagglutinin (HA) protein of human influenza A virus was introduced at the 5' end and at the 3' end of ORF7, in each case resulting in a fusion protein between the HA epitope and the nucleocapsid (N) protein. Furthermore, in the construct carrying the HA sequences at the 5' end of ORF7, additional in-frame insertions encoding the autoprotease 2A of foot-and-mouth disease virus were made between the HA and ORF7 sequences to ensure the generation of a functional N protein from its hybrid precursor. When RNA transcripts from these full-length cDNA clones were transfected into BHK-21 cells, they were each found to replicate, to express the HA epitope, and to produce progeny virus. However, fusion of the HA epitope directly to the nucleocapsid protein either at the N terminus or at the C terminus adversely affected both the viability and the genetic stability of the recombinant PRRS viruses. Serial passage of the recombinant viruses on porcine alveolar macrophages demonstrated that these viruses had lost (part of) the HA epitope at passage four. In contrast, in the PRRS viruses expressing the HA epitope from a precursor cleavable by the autoprotease 2A peptide, the HA epitope was still intact after four passages, and no effect on the viability of these viruses was observed. Immunoprecipitation and pulse chase experiments revealed the efficient and presumably cotranslational cleavage of the HA epitope from the N protein by the 2A protease. Our results demonstrate the feasibility of using PRRSV as a viral vector that might be suitable for the delivery of antigens from other pathogens to the immune system of the pig.

PACSIN2 is a regulator of the metalloprotease/disintegrin ADAM13

ADAM13 is a cell surface metalloprotease expressed in cephalic neural crest cells during early Xenopus development. The cytoplasmic domain of ADAM13 contains three potential SH3 (Src homology type 3) binding sites, suggesting that this region may support interactions with intracellular proteins. In this report we describe the identification, by a new strategy, of three proteins that bind the ADAM13 cytoplasmic domain in vitro: X-Src1, X-An4, and X-PACSIN2. We focused our study on X-PACSIN2 protein because it colocalizes with ADAM13 in migrating neural crest cells during embryonic development. Using pull-down experiments we show that X-PACSIN2 binds to ADAM13 in vitro. Using Xenopus XTC cells, we demonstrate that ADAM13 and X-PACSIN2 colocalize to membrane ruffles and cytoplasmic vesicles. We also show that X-PACSIN2 overexpression can rescue developmental alterations induced by overexpression of ADAM13, suggesting that both proteins interact in vivo. Finally, our results suggest that X-PACSIN2 overexpression reduces endogenous ADAM13 function while a truncated X-PACSIN2 (DeltaSH3) increases this activity in cephalic neural crest cells. We propose that X-PACSIN2 may regulate ADAM13 activity by influencing either its subcellular localization or its catalytic activity. In agreement with this model, elimination of the ADAM13 cytoplasmic domain increased developmental alterations attributable to ADAM13 proteolytic activity.