A disulfide bridge network within the soluble periplasmic domain determines structure and function of the outer membrane protein RCSF

RcsF, a proposed auxiliary regulator of the regulation of capsule synthesis (rcs) phosphorelay system, is a key element for understanding the RcsC-D-A/B signaling cascade, which is responsible for the regulation of more than 100 genes and is involved in cell division, motility, biofilm formation, and virulence. The RcsC-D-A/B system is one of the most complex bacterial signal transduction pathways, consisting of several membrane-bound and soluble proteins. RcsF is a lipoprotein attached to the outer membrane and plays an important role in activating the RcsC-d-A/B pathway. The exact mechanism of activation of the rcs phosphorelay by RcsF, however, remains unknown. We have analyzed the sequence of RcsF and identified three structural elements: 1) an N-terminal membrane-anchored helix (residues 3-13), 2) a loop (residues 14-48), and 3) a C-terminal folded domain (residues 49-134). We have determined the structure of this C-terminal domain and started to investigate its interaction with potential partners. Important features of its structure are two disulfide bridges between Cys-74 and Cys-118 and between Cys-109 and Cys-124. To evaluate the importance of this RcsF disulfide bridge network in vivo, we have examined the ability of the full-length protein and of specific Cys mutants to initiate the rcs signaling cascade. The results indicate that the Cys-74/Cys-118 and the Cys-109/Cys-124 residues correlate pairwise with the activity of RcsF. Interaction studies showed a weak interaction with an RNA hairpin. However, no interaction could be detected with reagents that are believed to activate the rcs phosphorelay, such as lysozyme, glucose, or Zn(2+) ions.     

Heterochromatin protein (HP)1γ is not only in the nucleus but also in the cytoplasm interacting with actin in both cell compartments

Confocal and electron microscopy images, and WB analysis of cellular fractions revealed that HP1γ is in the nucleus but also in the cytoplasm of C2C12 myoblasts, myotubes, skeletal and cardiac muscles, N2a, HeLa and HEK293T cells. Signal specificity was tested with different antibodies and by HP1γ knockdown. Leptomycin B treatment of myoblasts increased nuclear HP1γ, suggesting that its nuclear export is Crm-1-dependent. HP1γ exhibited a filamentous pattern of staining partially co-localizing with actin in the cytoplasm of myotubes and myofibrils. Immunoelectron microscopic analysis showed high-density immunogold particles that correspond to HP1γ localized to the Z-disk and A-band of the sarcomere of skeletal muscle. HP1γ partially co-localized with actin in C2C12 myotubes and murine myofibrils. Importantly, actin co-immunoprecipitated with HP1γ in the nuclear and cytosolic fractions of myoblasts. Actin co-immunoprecipitated with HP1γ in myoblasts incubated in the absence or presence of the actin depolymerizing agent cytochalasin D, suggesting that HP1γ may interact with G-and F-actin. In the cytoplasm, HP1γ was associated to the perinuclear actin cap that controls nuclear shape and position. In the nucleus, re-ChIP assays showed that HP1γ-actin associates to the promoter and transcribed regions of the house keeping gene GAPDH, suggesting that HP1γ may function as a scaffold protein for the recruitment of actin to control gene expression. When HP1γ was knocked-down, myoblasts were unable to differentiate or originated thin myotubes. In summary, HP1γ is present in the nucleus and the cytoplasm interacting with actin, a protein complex that may exert different functions depending on its subcellular localization.     

An automated small-scale protein expression and purification screening provides beneficial information for protein production

One of the first key steps in structural genomics is high-throughput expression and rapid screening to select highly soluble proteins, the preferred candidates for crystal production. Here we describe the methodology used at the Berkeley Structural Genomics Center (BSGC) for automated parallel expression and small-scale purification of fusion proteins using a 96-well format. Our robotic method includes cell lysis, soluble fraction separation and purification with affinity resins. For detection of His-tagged proteins in the soluble fractions and after affinity resin elution, a dot-blot procedure with an anti-His-antibody is used. The expression level and molecular mass of recombinant proteins are checked by SDS-PAGE. With this approach, we are able to obtain beneficial information to be used for large-scale protein expression and purification.     

Characterization and phenotypic variation with passage number of cultured human endometrial adenocarcinoma cells

Despite numerous endometrial cancer cell lines, little is know about the progression and transition of primary cultured endometrial tumours. Herein, a stage I grade III endometrial adenocarcinoma was maintained in primary culture and the phenotypic and protein expression changes were observed in relation to passage number. At early passage numbers, cultured human endometrial cancer (CHEC) cells displayed classic epithelial cell morphology, growing in groups in a glandular structure and staining positive for cytokeratin. However, with increasing passage number, CHEC cells changed in morphology to display a stromal phenotype which was accompanied by a significant reduction in cytokeratin and increases in alpha-actin and vimentin expression. Simultaneous culture of stromal cells isolated from the original tumour failed to show the same morphological characteristics or protein expression patterns. We further characterised CHEC cells through a screening of cancer related proteins, among others, caveolin-1 and Tissue factor in comparison with established cancer cell lines and corresponding non-cancerous cells. This report demonstrates that endometrial adenocarcinoma cells in culture can undergo phenotypic and protein expression changes reminiscent of epithelial-mesenchymal transition. This work suggests that primary tumours and cell lines displaying stromal morphologies may have undergone epithelial-mesenchymal transition from an adenocarcinoma origin.     

Identification and characterization of NBS-LRR class resistance gene analogs in faba bean (Vicia faba L.) and chickpea (Cicer arietinum L.).

A PCR approach with degenerate primers designed from conserved NBS-LRR (nucleotide binding site-leucine-rich repeat) regions of known disease-resistance (R) genes was used to amplify and clone homologous sequences from 5 faba bean (Vicia faba) lines and 2 chickpea (Cicer arietinum) accessions. Sixty-nine sequenced clones showed homologies to various R genes deposited in the GenBank database. The presence of internal kinase-2 and kinase-3a motifs in all the sequences isolated confirm that these clones correspond to NBS-containing genes. Using an amino-acid sequence identity of 70% as a threshold value, the clones were grouped into 10 classes of resistance-gene analogs (RGA01 to RGA10). The number of clones per class varied from 1 to 30. RGA classes 1, 6, 8, and 9 were comprised solely of clones isolated from faba bean, whereas classes 2, 3, 4, 5, and 7 included only chickpea clones. RGA10, showing a within-class identity of 99%, was the only class consisting of both faba bean and chickpea clones. A phylogenetic tree, based on the deduced amino-acid sequences of 12 representative clones from the 10 RGA classes and the NBS domains of 6 known R genes (I2 and Prf from tomato, RPP13 from Arabidopsis, Gro1-4 from potato, N from tobacco, L6 from flax), clearly indicated the separation between TIR (Toll/interleukin-1 receptor homology: Gro1-4, L6, N, RGA05 to RGA10)- and non-TIR (I2, Prf, RPP13, RGA01 to RGA04)-type NBS-LRR sequences. The development of suitable polymorphic markers based on cloned RGA sequences to be used in genetic mapping will facilitate the assessment of their potential linkage relationships with disease-resistance genes in faba bean and chickpea. This work is the first to report on faba bean RGAs.     

A 45‐bp Insertion/Deletion Polymorphism of Uncoupling Protein 2 in Relation to Obesity in Tongans

We compared the current prevalence of increased BMI and type 2 diabetes in a representative group of Tongan subjects with measurements made in 1973, and we determined the distribution and possible interrelations with the UCP2 insertion/deletion (ins/del) polymorphism of these variables. We documented the BMI, glucose tolerance, and standard lipid variables in 1012 Tongan subjects (429 men and 583 women, ages 15 to 85 years) during 1998 and 2000 and compared the BMI findings with those of the 1973 survey. We also genotyped for the UCP2 ins/del polymorphism, assessed its association with obesity and type 2 diabetes, and compared its prevalence with those reported for other ethnic populations. The mean BMI ± SD was greatly increased in both men (30.2 ± 5.4 kg/m²) and women (33.8 ± 6.2 kg/m²), representing increases since 1973 of 11.9% and 19.4%, respectively. The genotype frequencies were 97% for the del/del genotype and 3% for the ins/del genotype; we found no ins/ins homozygotes. This distribution is strikingly different from those reported for white, South Indian, Pima Native‐American, and Asian populations (49 to 77% for del/del genotype). We conclude that there is a marked prevalence of obesity in Tonga, a prevalence that has increased since 1973. We also conclude that there is a unique, near‐uniform distribution of the UCP2 45‐bp ins/del polymorphism in Tongans. This may be the result of a founder effect and may be relevant to the prevalence of obesity and type 2 diabetes in Tonga.