Polyproline type II conformation in the C-terminal domain of the nuclear pore complex protein gp210

Static light scattering and small-angle neutron scattering study on aggregated recombinant gelatin in aqueous solution

Recombinant gelatins are currently evaluated as new excipients for pharmaceutical formulations. They can differ from nonrecombinant gelatins because of intentional alteration of the amino acid sequence and specific properties of the expression systems used. This may affect their solution behavior. In the present work, aqueous solutions of a histidine-containing recombinant gelatin (RG-15-His) were analyzed. Dynamic light scattering (DLS) and loss of absorbance at 200 nm upon centrifugation indicated the formation of aggregates within 1 day upon sample preparation. Static light scattering (SLS) and small-angle neutron scattering (SANS) experiments showed that the aggregate's size was > or =300 nm, and that aggregates are composed of thin, rigid rods of 37 +/- 5 nm in length. The observed aggregation was not detectable by circular dichroism (CD), Fourier transform infrared spectroscopy (FTIR), and cryo transmission electron microscopy (cryo-TEM). SANS experiments, which are not frequently used in the pharmaceutical field, provided additional morphological information about the recombinant gelatin in solution. The results show that combining SLS and SANS is a broadly applicable, complementary approach for detecting aggregation of proteins and other biomolecules and for obtaining structural information about the aggregates.

Despite WT1 binding sites in the promoter region of human and mouse nucleoporin glycoprotein 210, WT1 does not influence expression of GP210

Background

Glycoprotein 210 (GP210) is a transmembrane component of the nuclear pore complex of metazoans, with a short carboxyterminus protruding towards the cytoplasm. Its function is unknown, but it is considered to be a major structural component of metazoan nuclear pores. Yet, our previous findings showed pronounced differences in expression levels in embryonic mouse tissues and cell lines. In order to identify factors regulating GP210, the genomic organization of human GP210 was analyzed in silico.

Results

The human gene was mapped to chromosome 3 and consists of 40 exons spread over 102 kb. The deduced 1887 amino acid showed a high degree of alignment homology to previously reported orthologues. Experimentally we defined two transcription initiation sites, 18 and 29 bp upstream of the ATG start codon. The promoter region is characterized by a CpG island and several consensus binding motifs for gene regulatory transcription factors, including clustered sites associated with Sp1 and the Wilms' tumor suppressor gene zinc finger protein (WT1). In addition, distal to the translation start we found a (GT)n repetitive sequence, an element known for its ability to bind WT1. Homologies for these motifs could be identified in the corresponding mouse genomic region. However, experimental tetracycline dependent induction of WT1 in SAOS osteosarcoma cells did not influence GP210 transcription.

Conclusion

Although mouse GP210 was identified as an early response gene during induced metanephric kidney development, and WT1 binding sites were identified in the promoter region of the human GP210 gene, experimental modulation of WT1 expression did not influence expression of GP210. Therefore, WT1 is probably not regulating GP210 expression. Instead, we suggest that the identified Sp binding sites are involved.

A Natively Unfolded Toxin Domain Uses Its Receptor as a Folding Template

Natively unfolded proteins range from molten globules to disordered coils. They are abundant in eukaryotic genomes and commonly involved in molecular interactions. The essential N-terminal translocation domains of colicin toxins from Escherichia coli are disordered bacterial proteins that bind at least one protein of the Tol or Ton family. The colicin N translocation domain (ColN-(1-90)), which binds to the C-terminal domain of TolA (TolA-(296-421)), shows a disordered far-UV CD spectrum, no near-UV CD signal, and non-cooperative thermal unfolding. As expected, TolA-(296-421) displays both secondary structure in far-UV CD and tertiary structure in near-UV CD. Furthermore it shows a cooperative unfolding transition at 65 degrees C. CD spectra of the 1:1 complex show both increased secondary structure and colicin N-specific near-UV CD signals. A new cooperative thermal transition at 35 degrees C is followed by the unchanged unfolding behavior of TolA-(296-421). Fluorescence and surface plasmon resonance confirm that the new unfolding transition accompanies dissociation of ColN-(1-90). Hence upon binding the disordered structure of ColN-(1-90) converts to a cooperatively folded domain without altering the TolA-(296-421) structure.

Limited expression of nuclear pore membrane glycoprotein 210 in cell lines and tissues suggests cell-type specific nuclear pores in metazoans

The nuclear pore complex (NPC) is the only known gateway for nucleocytoplasmic traffic. The nuclear pore membrane glycoprotein 210 (POM210/gp210) is considered to be important for the assembly and structure of pore complexes in metazoan cells. However, here we demonstrate cell-type specific expression of the gp210 protein during mouse organogenesis. As shown previously for its mRNA, distinct expression of the gp210 was seen in developing epithelia and some other cell types, whereas it was undetectable in nuclei of several other embryonic tissue compartments. In sharp contrast, monoclonal antibody 414 recognizing four non-membrane nucleoporins, stained the nuclear envelope of all cell types. In four cultured mouse cell lines, gp210 mRNA and protein were below detection levels, in contrast to some other nucleoporins tested. Distinct expression of gp210 mRNA and protein was seen in cultured mouse embryonic stem (ES) cells. These findings support the view of cell-type specific NPCs in metazoans and that the gp210 gene is regulated by cell-type specific control elements not shared by other nucleoporins. Although it cannot be excluded that very low expression levels of gp210 are sufficient to allow attachment of NPCs, a more likely alternative is that it has cell-type specific functions.

Nuclear pore protein gp210 is essential for viability in HeLa cells and Caenorhabditis elegans

Gp210 is an evolutionarily conserved membrane protein of the nuclear pore complex (NPC). We studied the phenotypes produced by RNAi-induced downregulation of gp210 in both human (HeLa) cells and Caenorhabditis elegans embryos. HeLa cell viability requires Gp210 activity. The dying cells accumulated clustered NPCs and aberrant membrane structures at the nuclear envelope, suggesting that gp210 is required directly or indirectly for nuclear pore formation and dilation as well as the anchoring or structural integrity of mature NPCs. Essential roles for gp210 were confirmed in C. elegans, where RNAi-induced reduction of gp210 caused embryonic lethality. The nuclear envelopes of embryos with reduced gp210 also had aberrant nuclear membrane structures and clustered NPCs, confirming that gp210 plays critical roles at the nuclear membrane through mechanisms that are conserved from nematodes to humans.