Downregulation of the NbNACa1 gene encoding a movement-protein-interacting protein reduces cell-to-cell movement of Brome mosaic virus in Nicotiana benthamiana

The 3a movement protein (MP) plays a central role in the movement of the RNA plant virus, Brome mosaic virus (BMV). To identify host factor genes involved in viral movement, a cDNA library of Nicotiana benthamiana, a systemic host for BMV, was screened with far-Western blotting using a recombinant BMV MP as probe. One positive clone encoded a protein with sequence similarity to the alpha chain of nascent-polypeptide-associated complex from various organisms, which is proposed to contribute to the fidelity of translocation of newly synthesized proteins. The orthologous gene from N. benthamiana was designated NbNACa1. The binding of NbNACa1 to BMV MP was confirmed in vivo with an agroinfiltration-immunoprecipitation assay. To investigate the involvement of NbNACa1 in BMV multiplication, NbNACa1-silenced (GSNAC) transgenic N. benthamiana plants were produced. Downregulation of NbNACa1 expression reduced virus accumulation in inoculated leaves but not in protoplasts. A microprojectile bombardment assay to monitor BMV-MP-assisted viral movement demonstrated reduced virus spread in GSNAC plants. The localization to the cell wall of BMV MP fused to green fluorescent protein was delayed in GSNAC plants. From these results, we propose that NbNACa1 is involved in BMV cell-to-cell movement through the regulation of BMV MP localization to the plasmodesmata.

Borreliacidal OspC antibody response of canines with Lyme disease differs significantly from that of humans with Lyme disease

Humans reliably produce high concentrations of borreliacidal OspC antibodies specific for the seven C-terminal amino acids shortly after infection with Borrelia burgdorferi. We show that dogs also produce OspC borreliacidal antibodies but that their frequencies, intensities, and antigenicities differ significantly. The findings therefore confirm a major difference between the borreliacidal antibody responses of humans and canines with Lyme disease.

Characterization of novel Bruton's tyrosine kinase gene mutations in Central European patients with agammaglobulinemia

X-linked agammaglobulinemia (XLA) is an immunodeficiency disorder caused by mutations in the gene coding for Bruton's tyrosine kinase (BTK). In this study we investigated 10 male patients with XLA-compatible phenotype (agammaglobulinemia and undetectable B cells in peripheral blood) from 9 unrelated Central European families. We identified seven different mutations, six of which were novel. One previously described point mutation caused a premature stop codon (p.C464X), two point mutations resulted in amino acid exchanges (p.W588R; p.G419E), and two point mutations affected splice sites (c.305-1G>A; c.391+1G>A). We further detected one deletion (c.1921_1927del CGTCCCA) and one large duplication. The duplication resulted from Alu element-induced unequal homologous recombination, which was only detectable by extended analysis of cDNA, while direct sequencing of genomic DNA gave a false negative result. Western blot analysis revealed that the patients with the p.W588R and the p.G419E amino acid substitutions, respectively, produced full length BTK, but in clearly diminished amounts. The patient with the 7bp deletion expressed low amounts of protein which might represent truncated BTK. All other genomic alterations resulted in complete loss of BTK protein. In two patients from unrelated families BTK protein expression was normal and no Btk gene mutation was detected. The results of this study further substantiate the importance of using elaborate molecular analysis with different detection techniques to obtain an explicit molecular diagnosis in patients with suspected XLA.

The Spt6 SH2 domain binds Ser2-P RNAPII to direct Iws1-dependent mRNA splicing and export

Spt6 promotes transcription elongation at many genes and functions as a histone H3 chaperone to alter chromatin structure during transcription. We show here that mammalian Spt6 binds Ser2-phosphorylated (Ser2P) RNA polymerase II (RNAPII) through a primitive SH2 domain, which recognizes phosphoserine rather than phosphotyrosine residues. Surprisingly, a point mutation in the Spt6 SH2 domain (R1358K) blocked binding to RNAPIIo without affecting transcription elongation rates in vitro. However, HIV-1 and c-myc RNAs formed in cells expressing the mutant Spt6 protein were longer than normal and contained splicing defects. Ectopic expression of the wild-type, but not mutant, Spt6 SH2 domain, caused bulk poly(A)+ RNAs to be retained in the nucleus, further suggesting a widespread role for Spt6 in mRNA processing or assembly of export-competent mRNP particles. We cloned the human Spt6-interacting protein, hIws1 (interacts with Spt6), and found that it associates with the nuclear RNA export factor, REF1/Aly. Depletion of endogenous hIws1 resulted in mRNA processing defects, lower levels of REF1/Aly at the c-myc gene, and nuclear retention of bulk HeLa poly(A)+ RNAs in vivo. Thus binding of Spt6 to Ser2-P RNAPII provides a cotranscriptional mechanism to recruit Iws1, REF1/Aly, and associated mRNA processing, surveillance, and export factors to responsive genes.

Vimentin Expressed onMycobacterium tuberculosis-Infected Human Monocytes Is Involved in Binding to the NKp46 Receptor

We previously showed that human NK cells used the NKp46 receptor to lyse Mycobacterium tuberculosis H37Ra-infected monocytes. To identify ligands on H37Ra-infected human mononuclear phagocytes, we used anti-NKp46 to immunoprecipitate NKp46 from NK cells bound to its ligand(s) on H37Ra-infected monocytes. Mass spectrometry analysis identified a 57-kDa molecule, vimentin, as a putative ligand for NKp46. Vimentin expression was significantly up-regulated on the surface of infected monocytes, compared with uninfected cells, and this was confirmed by fluorescence microscopy. Anti-vimentin antiserum inhibited NK cell lysis of infected monocytes, whereas antiserum to actin, another filamentous protein, did not. CHO-K1 cells transfected with a vimentin construct were lysed much more efficiently by NK cells than cells transfected with a control plasmid. This lysis was inhibited by mAb-mediated masking of NKp46 (on NK cells) or vimentin (on infected monocytes). ELISA and Far Western blotting showed that recombinant vimentin bound to a NKp46 fusion protein. These results indicate that vimentin is involved in binding of NKp46 to M. tuberculosis H37Ra-infected mononuclear phagocytes.

Molecular and functional interactions between Escherichia coli nucleoside-diphosphate kinase and the uracil-DNA glycosylase Ung

Escherichia coli nucleoside-diphosphate kinase (Ndk) catalyzes nucleoside triphosphate synthesis and maintains intracellular triphosphate pools. Mutants of E. coli lacking Ndk exhibit normal growth rates but show a mutator phenotype that cannot be entirely attributed to the absence of Ndk catalytic activity or to an imbalance in cellular triphosphates. It has been suggested previously that Ndk, similar to its human counterparts, possesses nuclease and DNA repair activities, including the excision of uracil from DNA, an activity normally associated with the Ung and Mug uracil-DNA glycosylases (UDGs) in E. coli. Here we have demonstrated that recombinant Ndk purified from wild-type E. coli contains significant UDG activity that is not intrinsic, but rather, is a consequence of a direct physical and functional interaction between Ung and Ndk, although a residual amount of intrinsic UDG activity exists as well. Co-purification of Ung and Ndk through multicolumn low pressure and nickel-nitrilotriacetic acid affinity chromatography suggests that the interaction occurs in a cellular context, as was also suggested by co-immunoprecipitation of endogenous Ung and Ndk from cellular extracts. Glutathione S-transferase pulldown and far Western analyses demonstrate that the interaction also occurs at the level of purified protein, suggesting that it is specific and direct. Moreover, significant augmentation of Ung catalytic activity by Ndk was observed, suggesting that the interaction between the two enzymes is functionally relevant. These findings represent the first example of Ung interacting with another E. coli protein and also lend support to the recently discovered role of nucleoside-diphosphate kinases as regulatory components of multiprotein complexes.

Functional significance of factor H binding to Neisseria meningitidis

Neisseria meningitidis is an important cause of septicemia and meningitis. To cause disease, the bacterium must successfully survive in the bloodstream where it has to avoid being killed by host innate immune mechanisms, particularly the complement system. A number of pathogenic microbes bind factor H (fH), the negative regulator of the alternative pathway of complement activation, to promote their survival in vivo. In this study, we show that N. meningitidis binds fH to its surface. Binding to serogroups A, B, and C N. meningitidis strains was detected by FACS and Far Western blot analysis, and occurred in the absence of other serum factors such as C3b. Unlike Neisseria gonorrhoeae, binding of fH to N. meningitidis was independent of sialic acid on the bacterium, either as a component of its LPS or its capsule. Characterization of the major fH binding partner demonstrated that it is a 33-kDa protein; examination of insertion mutants showed that porins A and B, outer membrane porins expressed by N. meningitidis, do not contribute significantly to fH binding. We examined the physiological consequences of fH bound to the bacterial surface. We found that fH retains its activity as a cofactor of factor I when bound to the bacterium and contributes to the ability of N. meningitidis to avoid complement-mediated killing in the presence of human serum. Therefore, the recruitment of fH provides another mechanism by which this important human pathogen evades host innate immunity.

A functional proteomics approach for the detection of nuclear proteins based on derepressed importin alpha

The identification of functional proteomes is a major challenge in proteomic research. Here we describe a method for the detection and isolation of nuclear (localization sequence containing) proteins using a derepressed import receptor (DIRE) as a synthetic antibody. We demonstrate that the DIRE method specifically detects nuclear localization sequence containing proteins. Application to activation of primary T-lymphocytes exemplifies the potential use of DIRE for comparative proteomics and for diagnostics.

Pleckstrin homology domain of phospholipase C-γ1 directly binds to 68-kDa neurofilament light chain

Phosphoinositide-specific phospholipase C-gamma1 (PLC-gamma1) has two pleckstrin homology (PH) domains: an amino-terminal domain (PH1) and a split PH domain (PH2). Here, we show that overlay assay of bovine brain tubulin pool with glutathione-S-transferase (GST)-PLC-gamma1 PH domain fusion proteins, followed by matrix-assisted laser-desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), identified 68-kDa neurofilament light chain (NF-L) as a binding protein of amino-terminal PH domain of PLC-gamma1. NF-L is known as a component of neuronal intermediate filaments, which are responsible for supporting the structure of myelinated axons in neuron. PLC-gamma1 and NF-L colocalized in the neurite in PC12 cells upon nerve growth factor stimulation. In vitro binding assay and immunoprecipitation analysis also showed a specific interaction of both proteins in differentiated PC12 cells. The phosphatidylinositol 4, 5-bisphosphate [PI(4,5)P(2)] hydrolyzing activity of PLC-gamma1 was slightly decreased in the presence of purified NF-L in vitro, suggesting that NF-L inhibits PLC-gamma1. Our results suggest that PLC-gamma1-associated NF-L sequesters the phospholipid from the PH domain of PLC-gamma1.

Evaluation of murine monoclonal antibodies targeting different epitopes of the hepatitis B virus surface antigen by using immunological as well as molecular biology and biochemical approaches

The hepatitis B virus surface protein (HBsAg) displays the major B cells antigenic determinants that can induce protective immunity and prevent the hepatitis B virus (HBV) infection, a major health problem. A panel of murine monoclonal antibodies against the HBsAg (MAb anti-HBs), raised after mice immunization with a pool of plasma of hepatitis chronic carriers, has been established. Mainly using simple immunological tools such as enzyme-linked immunosorbent assay (ELISA) and Western blot analysis, we could trace the location of the epitopes on the HBsAg determinants. We also report the use of two specific methodology approaches based on molecular biology and biochemical techniques such as, respectively, cloning and expression of preS1 major neutralizing epitope of the HBsAg in Escherichia coli and ELISA accomplished to chemical reduction with dithiothreitol (DTT), which were able to complete the MAb anti-HBs characterization. Our results showed that the majority of the MAbs anti-HBs were directed to the HBV common determinant a. One MAb recognizes a discontinuous epitope present in all forms of the HBsAg when evaluated by Western blot.

Associations of protein 4.2 with band 3 and ankyrin

Protein-protein and protein-lipid interactions are thought to play the vital role in maintenance and deformation of red blood cell (RBC) membrane. Protein 4.2, a 76-KDa peripheral protein, binds to the cytoplasmic domain of band 3 (CDB3) and also interacts with ankyrin in RBCs. In order to explore the characteristics of protein 4.2-CDB3-ankyrin interactions, three protein 4.2-derived recombinant proteins encompassing amino acid residues 31-200, 1-300, and 187-260 respectively were expressed in Escherichia coli. Their interactions with CDB3 and ankyrin were investigated by using Far-Western blot and pull-down assay. The results showed that the CDB3-binding site of protein 4.2 is located in the region of residues 200-211 and the ankyrin-binding site is located in the region of residues 187-200 of protein 4.2. Our findings also suggested that the ankyrin D34 domain can interact directly with protein 4.2. The proper tertiary structures of these protein 4.2 fragments are essential for protein 4.2-ankyrin interaction. Meanwhile, ankyrin can enhance the interaction between protein 4.2 and CDB3.

Identification and characterization of oviductal glycoprotein-binding protein partner on gametes: epitopic similarity to non-muscle myosin IIA, MYH 9

The mammalian estrogen induced oviductal glycoprotein (OGP) has been known to associate with capacitated sperm, oocytes and developing embryos. This study aimed to identify the putative binding partner of OGP on gametes using N-terminal peptide of bonnet monkey (Macaca radiata) OGP, Nmon, as bait. A protein(s) of molecular size approximately 54 kDa was detected by far-western blot analysis of detergent solubilized human sperm proteins. MALDI-TOF mass spectra analysis of approximately 54 kDa tryptic peptides gave a significant hit to non-muscle myosin heavy chain. Biochemical characterization of approximately 54 kDa was done with antibodies specific to non-muscle myosin IIA, MYH9. The approximately 54 kDa protein, possible breakdown product of MYH9, immunoreacted with MYH9 antibody in western blot analysis. OGP binding to approximately 54 kDa could also be demonstrated in far-western blot analysis of detergent solubilized human sperm proteins and nuclear matrix intermediate filament (NM-IF) preparations from human sperm and mouse oocytes. Far-western blot analysis of MYH9 enriched by immunoprecipitation identified the native approximately 220 kDa protein as OGP-binding partner. The identical and characteristic immunogold localization pattern of Nmon and MYH9 on sperm NM-IF preparation substantiated these findings. The results suggest that OGP binds to both gametes through its interaction with MYH9 through the non-glycosylated N-terminal conserved region of OGP, spanning the residues 11-137.

[Effects of peroxisome proliferators-activated receptor gamma agonists on transforming growth factor-beta1 and Smads signal pathway: experiment with rat renal fibroblasts]

OBJECTIVE

To study the effects of peroxisome proliferators-activated receptor gamma (PPARgamma) agonists on transforming growth factor (TGF)-beta1-induced fibrotic responses in renal fibroblasts, so as to investigate its effects in prevention of tubulointerstitial fibrosis.

METHODS

Rat renal fibroblasts of the line NRK/49F were cultured and divided into groups. In group 1 TGFbeta1 of the concentrations of 0, 1, 2, 5, and 10 ng/ml was added and co-cultured for 24 h. In group 2 TGFbeta1 of the concentration of 5 ng/ml was added and co-cultured for 0, 6, 12, and 24 h respectively. Groups 3, 4, and 5 were pretreated with 10 micromol/L15d-PGJ2, PPARgamma ligand, 10 micromol/L troglitazone, agonist of, and 10 micromol/L ciglitazone, both PPARgamma agonists, respectively for 2 h, then treated with 5 ng/ml TGFbeta1. A blank control group was set up. The cultured cells were collected. RT-PCR was used to detect the mRNA expression of TGF-beta1-indued fibronectin (FN). Western blotting was used to detect the expression of TGF-beta1-induced FN, Smad, and phosphorylated Smad (p-Smad) proteins.

RESULTS

TGF-beta1 enhanced the FN mRNA expression in a dose- and time-dependent manner. The FN mRNA expression of the 5 ng/ml TGF-beta1 group was 3.7 times that of the control group (P < 0.05). The FN mRNA expression of the 15d-PGJ2, troglitazone-, and ciglitazone-pretreated groups were lower than that of the 5 ng/ml TGF-beta1 group by 37.3%, 41.5%, and 22.7% respectively (all P < 0.05). The p-Smad2/3 protein expression levels of the TGF-beta1 group began to increase 15 minutes after stimulation, increased in a time-dependent manner, peaked 1 hour after, and began to decrease 2 hours later. However, the levels of protein expression of total Smad2 and Smad3 did not change significantly in all groups. Both 2 ng/ml TGFbeta1 and 5 ng/ml TGFbeta1 significantly induced the increase of protein expression of p-Smad2/3 (all P < 0.05). The levels of protein expression of p-Smad2 and p-Smad3 of the 5 ng/ml TGFbeta1 group were 3.42 and 0.97 times those of the 2 ng/ml TGFbeta1 (both P < 0.05). The levels of protein expression of p-Smad2/3 of the 15d-PGJ2, troglitazone-, and ciglitazone-pretreated groups were all significantly lower than that of the 5 ng/ml TGFbeta1 group by 61.2%, 53.0%, and 59.5% (all P < 0.05), However, there was no significant difference among different drug-treated groups (all P > 0.05).

CONCLUSION

Possibly through abrogating TGF-beta1/Smads signaling pathway, PPARgamma agonists inhibit TGF-beta1-induced renal fibroblast extracellular matrix synthesis and may play a potential role in preventing tubulointerstitial fibrosis as a novel approach to prevent the progress of end stage renal dysfunction.

Characterization of a mouse amelogenin [A-4]/M59 cell surface receptor

Amelogenin proteins comprise up to 90% of the organic matrix of developing enamel in the vertebrate tooth. Alternative splicing of mouse amelogenin pre-mRNA leads to the production of more than 14 protein isoforms, the functions of which are not totally understood. The smaller splice products, [A + 4] or M73 and [A - 4] or M59, have been shown to act differently as signaling molecules affecting odontogenic and other cell types. The mechanisms of these signaling processes, beginning with receptor identification, are not well understood. Utilizing radiolabeled [A - 4], we show here that 3H[A - 4] binds in a saturable fashion to the cell surface of C2C12 mouse fetal myoblasts at 4 degrees C, and not only binds at the surface but is internalized at 37 degrees C. "Far Western" immunohistochemistry performed on sections of E18 mouse incisors and molars with biotin-labeled [A - 4] as the primary ligand demonstrates [A - 4]-biotin binding to polarizing ameloblasts and odontoblasts, cells of the dental follicle, and along the stratum intermedium. Using [A - 4] affinity column chromatography and [A - 4]-biotin label transfer reaction, we have identified a 95 kDa C2C12 cell surface protein which bound [A - 4]. Utilizing Tandem MS (MS/MS) sequencing, we report the novel finding of the 95 kDa murine transmembrane protein, LAMP-1, originally identified as a lysosomal membrane protein that is also found at the cell surface, as an [A - 4] cell binding protein.

Protective immunity against Streptococcus pyogenes challenge in mice after immunization with fibronectin-binding protein

BACKGROUND

Surface-associated fibronectin (Fn)-binding proteins of Streptococcus pyogenes play an important role in the bacterial invasion of epithelial cells. We examined the functional domain and protective antigenicity of the Fn-binding protein FbaA.

METHODS

To investigate the functional domain of FbaA and its localization on S. pyogenes, a series of recombinant glutathione S-transferase (GST)-truncated FbaA proteins was used for immunofluorescent microscopy, ligand blotting, and Biacore analyses. Mice were immunized with the truncated proteins for the determination of the immunogenic domains that contribute to protection against S. pyogenes infection.

RESULTS

Ligand-blotting and Biacore analyses revealed that the FbaA fragments harboring a proline-rich repeat domain (RD), but not the N- and C-terminal regions, possessed Fn-binding activity. Immunofluorescent microscopy findings showed that the N terminus and RD were exposed to external regions, which suggests that the RD serves as a Fn-binding element on live organisms. Specific antibodies were efficiently induced in N terminus- and RD-immunized mice and demonstrated bactericidal activity against S. pyogenes in vitro. FbaA-immunized mice survived significantly longer than GST-immunized mice after infection with serotype M1 and M49 strains expressing FbaA.

CONCLUSION

The Fn-binding RD and N terminus of FbaA are potential vaccine candidates for M1 strains of S. pyogenes infection.

Analysis of interactions between mismatch repair initiation factors and the replication processivity factor PCNA

In eukaryotes, the DNA replication factor PCNA is loaded onto primer-template junctions to act as a processivity factor for DNA polymerases. Genetic and biochemical studies suggest that PCNA also functions in early steps in mismatch repair (MMR) to facilitate the repair of misincorporation errors generated during DNA replication. These studies have shown that PCNA interacts directly with several MMR components, including MSH3, MSH6, MLH1, and EXO1. At present, little is known about how these interactions contribute to the mismatch repair mechanism. The interaction between MLH1 and PCNA is of particular interest because MLH1-PMS1 is thought to act as a matchmaker to signal mismatch recognition to downstream repair events; in addition, PCNA has been hypothesized to act in strand discrimination steps in MMR. Here, we utilized both genetic and surface plasmon resonance techniques to characterize the MLH1-PMS1-PCNA interaction. These analyses enabled us to determine the stability of the complex (K(D) = 300 nM) and to identify residues (572-579) in MLH1 and PCNA (126,128) that appear important to maintain this stability. We favor a model in which PCNA acts as a scaffold for consecutive protein-protein interactions that allow for the coordination of MMR steps.

Enhanced Yield and Homogeneity of Buffalo Growth Hormone by an Improved Chromatographic Protocol

Loss of buffalo Growth Hormone (buGH) in the various side fractions of standard buGH purification protocol has been determined quantitatively by direct binding ELISA and qualitatively by SDS-PAGE and Western blot analysis. Accounting result indicated that there was a considerable loss of buGH in the side fractions. An alternative protocol to prevent loss and to obtain a high yield of buGH has been developed by introducing anion exchange chromatography, QAE-Sephadex. This has resulted in a simple, reproducible three-step protocol. In this protocol, an extract obtained at 250 mM (NH4)2 SO4, pH 5.5, was loaded onto the QAE-Sephadex column in 0.1 M NH4 HCO3. At this salt concentration, the bulk of the buGH came as QAE unbound fraction. Some amount of buGH, together with contaminating proteins, was bound to QAE-Sephadex and these could be eluted with 1 M KCl. The immunopotency of the enriched buGH preparation "QUB" (QAE unbound fraction) in a direct binding ELISA was similar to that of the semi-pure buGH (ECS/APECS) preparation obtained using the standard protocol, but the yield was 4 times higher. The SDS-PAGE data showed that the banding pattern of standard semi-pure buGH and QUB were quite similar and QUB can be loaded onto the Sephacryl S-200 gel filtration chromatography to yield a highly purified buGH. SDS-PAGE and Western blot analyses showed the major band of buGH in QUB at the same position as in the case of standard buGH. It has also been demonstrated here that it is possible to separate buffalo prolactin (buPRL) and buGH on QAE-Sephadex.

Smooth muscle alpha-actinin interaction with smitin

Actin-myosin II filament-based contractile structures in striated muscle, smooth muscle, and nonmuscle cells also contain the actin filament-crosslinking protein alpha-actinin. In striated muscle sarcomeres, interactions between the myosin-binding protein titin and alpha-actinin in the Z-line provide an important structural linkage. We previously discovered a titin-like protein, smitin, associated with the contractile apparatus of smooth muscle cells. Purified native smooth muscle alpha-actinin binds with nanomolar affinity to smitin in smitin-myosin coassemblies in vitro. Smooth muscle alpha-actinin also interacts with striated muscle titin. In contrast to striated muscle alpha-actinin interaction with titin and smitin, which is significantly enhanced by PIP2, smooth muscle alpha-actinin interacts with smitin and titin equally well in the presence and absence of PIP2. Using expressed regions of smooth muscle alpha-actinin, we have demonstrated smitin-binding sites in the smooth muscle alpha-actinin R2-R3 spectrin-like repeat rod domain and a C-terminal domain formed by cryptic EF-hand structures. These smitin-binding sites are highly homologous to the titin-binding sites of striated muscle alpha-actinin. Our results suggest that direct interaction between alpha-actinin and titin or titin-like proteins is a common feature of actin-myosin II contractile structures in striated muscle and smooth muscle cells and that the molecular bases for alpha-actinin interaction with these proteins are similar, although regulation of these interactions may differ according to tissue.

Two-hybrid analysis of human salivary mucin MUC7 interactions

MUC7 is a low molecular weight monomeric mucin secreted by submandibular, sublingual and minor salivary glands. This mucin has been implicated in the non-immune host defense system in the oral cavity since it binds and agglutinates a variety of oral microbes. To investigate interactions between this mucin and other secretory salivary proteins, a submandibular gland prey library was screened with baits encoding the N- and C-terminal regions of MUC7 in the yeast two-hybrid system. The N-terminal region interacted with several secretory salivary proteins, whereas the C-terminal region did not. Interacting proteins included amylase, acidic proline-rich protein 2, basic proline-rich protein 3, lacrimal proline-rich protein 4, statherin and histatin 1. Formation of complexes between these proteins and the N-terminal region of MUC7 was confirmed in Far Western blotting experiments. Interactions between mucin and non-mucin proteins in saliva could protect complex partners from proteolysis, modulate the biological activity of complexed proteins or serve as a delivery system for distribution of secretory salivary proteins throughout the oral cavity.

Coevolution between nonhomologous but functionally similar proteins and their conserved partners in the Legionella pathogenesis system

Legionella pneumophila, the causative agent of Legionnaires' disease, and other pathogenic Legionella species multiply inside protozoa and human macrophages by using the intracellular multiplication (Icm)/defect in organelle trafficking (Dot) type-IV secretion system. The IcmQ protein, which possesses pore-forming activity, and IcmR, which regulates the IcmQ activity, are two essential components of this system. Analysis of the region expected to contain these two genes from 29 Legionella species revealed the presence of a conserved icmQ gene and a large hypervariable gene family [functional homologues of icmR (fir) genes], located at the icmR genomic position. Although hypervariable in their sequence, the fir genes from all 29 Legionella species were found, together with their corresponding icmQ genes, to function similarly during infection. In addition, all FIR proteins we examined were found to interact with their corresponding IcmQ proteins. Detailed bioinformatic, biochemical, and genetic analysis of the interaction between the variable FIR proteins and conserved IcmQ proteins revealed that their interaction depends on a variable region located between two conserved domains of IcmQ. This variable region was also found to be critical for IcmQ self-interaction, and the region probably coevolved with the corresponding FIR protein. A FIR-IcmQ pair was also found in Coxiella burnetii, the only known non-Legionella bacterium that contains an Icm/Dot system, indicating the significance of this protein pair for the function of this type-IV secretion system. We hypothesize that this gene variation, which is probably mediated by positive selection, plays an important role in the evolutionary arms race between the protozoan host cell and the pathogen.

Transforming growth factor-beta-activated kinase-1 (TAK1), a MAP3K, interacts with Smad proteins and interferes with osteogenesis in murine mesenchymal progenitors

TAK1 (transforming growth factor-beta-activated kinase-1), a MAP3K with considerable sequence similarity to Raf-1 and MEKK-1, has been identified as a transforming growth factor-beta/bone morphogenetic protein (BMP)-activated cytosolic component of the MAPK pathways. In this investigation, the molecular interactions between TAK1 and Smad proteins were characterized as well as their influence on BMP-mediated mesenchymal cell differentiation along the osteogenic/chondrogenic pathway. In co-immunoprecipitations we found an interaction of TAK1 with all Smads tested, R-Smads Smads1-5, the co-Smad Smad4, and the inhibitory Smads (I-Smad6 and I-Smad7). Smad interaction with TAK1 takes place through their MH2 domain. This interaction is dependent on the presence of an active kinase domain in TAK1. TAK1 dramatically interferes with R-Smad transactivation in reporter assays and affects subcellular distribution of Smad proteins. Activated TAK1 also interferes with BMP-dependent osteogenic development in murine mesenchymal progenitor cells (C3H10T 1/2). A potential TAK1-mediated apoptosis process could be excluded for these cells. Both synergistic and interfering influences of TAK1 on BMP-mediated Smad-signaling have been reported previously. We suggest that TAK1 is a factor that is involved in the fine-tuning of BMP effects during osteogenic development.

Class-Specific Binding of Two Aminoacyl-tRNA Synthetases to Annexin, a Ca2+- and Phospholipid-Binding Protein

Annexins are a family of Ca2+/phospholipid-binding proteins that have diverse functions. To understand the function of annexin in Physarum polycephalum, we searched for its binding proteins. Here we demonstrate the presence of two novel annexin-binding proteins. The homology search of partial amino acid sequences of these two proteins identified them as aminoacyl-tRNA synthetases (ARSs). Furthermore, antibody against aminoacyl-tRNA synthetases cross-reacted with one of two proteins. Our results imply the interaction between intracellular membrane dynamics and protein translation system, and may give a clue to understand the mechanism of some myositis diseases, which have been known to produce autoantibodies against ARSs.