Parkin potentiates ATP-induced currents due to activation of P2X receptors in PC12 cells

Loss-of-function mutations of the parkin gene causes an autosomal recessive juvenile-onset form of Parkinson's disease (AR-JP). Parkin was shown to function as a RING-type E3 ubiquitin protein ligase. However, the function of parkin in neuronal cells remains elusive. Here, we show that expression of parkin-potentiated adenosine triphosphate (ATP)-induced currents that result from activation of the P2X receptors which are widely distributed in the brain and involved in neurotransmission. ATP-induced inward currents were measured in mock-, wild-type or mutant (T415N)-parkin-transfected PC12 cells under the conventional whole-cell patch clamp configuration. The amplitude of ATP-induced currents was significantly greater in wild-type parkin-transfected cells. However, the immunocytochemical study showed no apparent increase in the number of P2X receptors or in ubiquitin levels. The increased currents were attenuated by inhibition of cAMP-dependent protein kinase (PKA) but not protein kinase C (PKC) or Ca2+ and calmodulin-dependent protein kinase (CaMKII). ATP-induced currents were also regulated by phosphatases and cyclin-dependent protein kinase 5 (CDK5) via dopamine and cyclic AMP-regulated phosphoprotein (DARPP-32), though the phosphorylation at Thr-34 and Thr-75 were unchanged or rather attenuated. We also tried to investigate the effect of alpha-synuclein, a substrate of parkin and also forming Lysine 63-linked multiubiquitin chains. Expression of alpha-synuclein did not affect the amplitude of ATP-induced currents. Our finding provides the evidence for a relationship between parkin and a neurotransmitter receptor, suggesting that parkin may play an important role in synaptic activity.     

Copper binding properties of a tau peptide associated with Alzheimer's disease studied by CD, NMR, and MALDI-TOF MS

We have previously reported the copper binding properties of R3 peptide (residues 318-335: VTSKCGSLGNIHHKPGGG, according to the longest tau protein) derived from the third repeat microtubule-binding domain of water-soluble tau protein. In this work, we have investigated copper binding properties of R2 peptide (residues 287-304: VQSKCGSKDNIKHVPGGG) derived from the second repeat region of tau protein. Similar to R3 peptide, R2 peptide also plays an important role in the formation of neurofibrillary tangles (NFTs) which is one of the two main biological characteristics of Alzheimer's disease (AD). Based on the copper binding properties of R2 peptide, the possible influences of the binding on the formation of NFTs were investigated. Results from circular dichroism (CD) spectra, nuclear magnetic resonance (NMR) spectroscopy, and matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) suggest that the binding is pH-dependent and stoichiometry-determined. In addition, these results also reveal that R2 peptide adopts a monomeric alpha-helical structure in aqueous solutions at physiological pH after the addition of 1 mol equiv. of Cu2+. Since alpha-helix structure is responsible for the formation of paired helical filaments (PHFs) which aggregate into NFTs, it is hypothesized that Cu2+ induces R2 peptide to self-assemble into a PHFs-like structure. Hence, it is postulated that Cu2+ plays an important role in the aggregation of R2 peptide and tau protein and that copper binding to R2 peptide may be another possible involvement in AD.     

Crystal structure of the RUN domain of the RAP2-interacting protein x

Rap2-interacting protein x (RPIPx) is a homolog of RPIP8, a specific effector of Rap2 GTPase. The N-terminal region of RPIP8, which contains the RUN domain, interacts with Rap2. Using cell-free synthesis and NMR, we determined that the region encompassing residues 83-255 of mouse RPIPx, which is 40-residues larger than the predicted RUN domain (residues 113-245), is the minimum fragment that forms a correctly folded protein. This fragment, the RPIPx RUN domain, interacted specifically with Rap2B in vitro in a nucleotide-dependent manner. The crystal structure of the RPIPx RUN domain was determined at 2.0 A of resolution by the multiwavelength anomalous dispersion (MAD) method. The RPIPx RUN domain comprises eight anti-parallel alpha-helices, which form an extensive hydrophobic core, followed by an extended segment. The residues in the core region are highly conserved, suggesting the conservation of the RUN domain-fold among the RUN domain-containing proteins. The residues forming a positively charged surface are conserved between RPIP8 and its homologs, suggesting that this surface is important for Rap2 binding. In the crystal the putative Rap2 binding site of the RPIPx RUN domain interacts with the extended segment in a segment-swapping manner.     

Development of an open source laboratory information management system for 2-D gel electrophoresis-based proteomics workflow

Background  

In the post-genome era, most research scientists working in the field of proteomics are confronted with difficulties in management of large volumes of data, which they are required to keep in formats suitable for subsequent data mining. Therefore, a well-developed open source laboratory information management system (LIMS) should be available for their proteomics research studies.     

How do neurons die in neurodegenerative diseases?

Given that neurons are post-mitotic cells, their life span is generally long enough to reach that of humans. However, sometimes neurons die without recognizable causes, as a result of a process called neurodegeneration. Apart from when gene mutations can be correlated with disease, it is difficult to pinpoint molecules that are responsible for neuronal death. Therefore, neurons living in a 'sick state' for many years might reveal important information about neuronal death. Systematic and extensive single-neuron analysis of 'sick' neurons is expected to provide clues to the mechanisms of neurodegeneration. Moreover, the elimination of putative triggering and promoting factors involved in neurodegenerative disease might prevent disease progression.     

Essential role of macrophages in the initiation of allergic rhinitis in mice sensitized intranasally once with cedar pollen: regulation of class switching of immunoglobulin in B cells by controlling interleukin-4 production in T cells of submandibular lymph nodes

The production of allergen-specific IgE antibodies (Abs) in allergen-sensitized patients or animals has a mutual relationship with the immunologic response leading to allergic rhinitis. We recently reported that, after an intranasal injection of cedar pollen into mice, an interleukin-4 (IL-4)-dependent increase in serum nonspecific IgE Abs was a prerequisite for the production of serum allergen-specific IgE Abs. Here, we explored which lymphoid organs were responsive to the intranasally injected allergen and how IL-4 and IgE Abs were produced in the lymphocytes. Time-dependent changes in the total cell numbers and in in vitro IgE Ab production in various lymphoid organs revealed that the submandibular lymph nodes were the main responsible organ. After treatment with allergen (for IgE production) or allergen and complete Freund's adjuvant (for IgG production), we separated submandibular lymph node cells into macrophage-, lymphocyte-, and granulocyte-rich populations by discontinuous Percoll density-gradient centrifugation. Unexpectedly, bulk cells, but not the lymphocyte- or macrophage-rich populations, produced significant amounts of IL-4, IgE, and IgG; whereas production was restored by addition of Mac-1(+) cells from the macrophage-rich to the lymphocyte-rich fraction. Furthermore, a combination of the lymphocyte-rich population (for IgG [or IgE]) production) and the macrophage-rich population (for IgE [or IgG]) production) produced a large amount of IgE (or IgG). These results indicate that, in the initiation of allergic rhinitis, macrophages in the submandibular lymph nodes are essential not only for IL-4 or immunoglobulin production, but also for class switching of immunoglobulin in lymphocytes.     

Solution structures of the double-stranded RNA-binding domains from RNA helicase A

RNA helicase A (RHA) is a highly conserved protein with multifaceted functions in the gene expression of cellular and viral mRNAs. RHA recognizes highly structured nucleotides and catalytically rearranges the various interactions between RNA, DNA, and protein molecules to provide a platform for the ribonucleoprotein complex. We present the first solution structures of the double-stranded RNA-binding domains (dsRBDs), dsRBD1 and dsRBD2, from mouse RHA. We discuss the binding mode of the dsRBDs of RHA, in comparison with the known dsRBD structures in their complexes. Our structural data provide important information for the elucidation of the molecular reassembly mediated by RHA.